LT3932/LT3932-1
36V, 2A Synchronous
Step-Down LED Driver
FEATURESDESCRIPTION±1.5% LED Current Regulation
nn ±1.2% Output Voltage Regulation
nn 5000:1/10000+:1 PWM Dimming at 100Hz(LT3932/LT3932-1)
nn 128:1 Internal PWM Dimmingnn Spread-Spectrum Frequency Modulation
nn Silent Switcher® Architecture for Low EMI
nn 3.6V to 36V Input Voltage Range
nn 0V to 36V LED String Voltage
nn 200kHz to 2MHz with SYNC Function
nn 99.9% Maximum Duty Cycle
nn 20:1 Analog or Duty Cycle LED Current Control
nn Open/Short LED Protection and Fault Indicationnn Accurate LED Current Sense with Monitor Output
nn Programmable UVLO
nn Thermally Enhanced 28-Pin (4mm × 5mm) QFN

The LT®3932 , featuring the Silent Switcher®architecture
to minimize EMI/EMC emissions, utilizes fixed-frequency,
peak current control and provides PWM dimming for astring of LEDs. The LED current is programmed by an analog voltage or the duty cycle of pulses at the CTRL pin. An
output voltage limit can be set with a resistor divider tothe FB pin.

APPLICATIONS

Additional features include an LED current monitor, anaccurate EN/UVLO pin threshold, open-drain fault reporting for open-circuit and short-circuit load conditions, andthermal shutdown.

nn

The switching frequency is programmable from 200kHz to
2MHz by an external resistor at the RT pin or by an external clock at the SYNC/SPRD pin. With the optional spread
spectrum frequency modulation enabled, the frequency
varies from 100% to 125% to reduce EMI. The LT3932
also includes a driver for an external, high side PMOS forPWM dimming and an internal PWM signal generator for
analog control of PWM dimming when an external signal is
not available. The LT3932-1 permits higher dimming ratios.

Automotive Lighting
Industrial and General Purpose Lighting
nn Machine Vision Systemsnnnn

All registered trademarks and trademarks are the property of their respective owners. Protectedby U.S. Patents including 7199560, 7321203, 9596728, 9642200 and other patents pending.

TYPICAL APPLICATION
2A LED Driver with Internal PWM Dimming
INTVCC
VIN
20V

VIN
274k
10µF

SW

EN/UVLO

2x1µF

Internal PWM Dimming

BST

110k
FB

LT3932

10k

VREF
100k
100k

SW
20V/DIV

VOUT

30.1k

2.2µF

22nF

8.2µH

COUT
100µF

2A MAXIL
1A/DIV

GND

CTRL
PWM

ISP
50mΩ

INTVCC
2.2µF

ISN

100k
FAULT

45.3k
2MHz
100nF

ISMON

ILED
1A/DIVPWM = 1.078V
2µs/DIV(8% PWM DUTY RATIO)

PWMTG
FAULT
SYNC/SPRD
SS
RT RP

PWMTG
10V/DIV

3932 TA01b

ISMON

VC
28.7k
7.8kHz

162k

9V

10nF
3932 TA01a

Rev B

Document Feedback

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1

LT3932/LT3932-1
ABSOLUTE MAXIMUM RATINGSPIN CONFIGURATION(Note 1)GND

BST

INTVCC

VIN

CTRL

EN/UVLOTOP VIEW

VIN, EN/UVLO.............................................................40V
ISP, ISN, and VOUT.....................................................40V
ISP – ISN................................................................±0.3V
CTRL and FB.............................................................3.3V
PWM, SYNC/SPRD, and FAULT....................................6V
SS and VC.................................................................3.3V
SW, BST, INTVCC, VREF, ISMON, PWMTG, RT,
and RP................................................................ (Note 2)
Operating Junction Temperature Range (Notes 3, 4)
LT3932E/LT3932I............................... –40°C to 125°C
LT3932H............................................. –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C

28 27 26 25 24 23
VREF

1

22 GNDSS

2

21 VIN

VC

3

FB

4

20 VIN
19 SW

29
GND

ISP

5

ISN

6

ISMON

7

16 VINFAULT

815 GND

18 SW
17 VIN

VOUT

PWMTG

PWM

SYNC/SPRD

RT

RP

9 10 11 12 13 14

UFD PACKAGE
28-LEAD (4mm × 5mm) PLASTIC QFNθJA = 25°C/W (MEASURED ON DC2286A)
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCBORDER INFORMATIONLEAD FREE FINISH

TAPE AND REELPART MARKING*PACKAGE DESCRIPTIONTEMPERATURE RANGE

LT3932EUFD#PBF

LT3932EUFD#TRPBF

3932

28-Lead (4mm × 5mm) Plastic QFN–40°C to 125°C

LT3932IUFD#PBF

LT3932IUFD#TRPBF

3932

28-Lead (4mm × 5mm) Plastic QFN–40°C to 125°C

LT3932HUFD#PBF

LT3932HUFD#TRPBF

3932

28-Lead (4mm × 5mm) Plastic QFN–40°C to 150°C

LT3932EUFD-1#PBF

LT3932EUFD-1#TRPBF

39321

28-Lead (4mm × 5mm) Plastic QFN–40°C to 125°C

LT3932IUFD-1#PBF

LT3932IUFD-1#TRPBF

39321

28-Lead (4mm × 5mm) Plastic QFN–40°C to 125°C

LT3932HUFD-1#PBF

LT3932HUFD-1#TRPBF

39321

28-Lead (4mm × 5mm) Plastic QFN–40°C to 150°C

Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.

ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN/UVLO = 5V unless otherwise noted.
PARAMETERCONDITIONSMINInput Voltage Range
VIN Pin Quiescent Current

TYP

MAX

UNITS

36

V

2.2

2.7
2

mA
µA

1.15

1.21

V

3.6
EN/UVLO = 2V, Not Switching
EN/UVLO = 300mV, Shutdown

EN/UVLO Threshold (Falling)

l

1.09

EN/UVLO Rising Hysteresis

20mV

EN/UVLO Pin Hysteresis Current

4

µA

2

Rev B

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LT3932/LT3932-1
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN/UVLO = 5V unless otherwise noted.
PARAMETERCONDITIONS

MIN

TYP

MAX

UNITS

1.975
1.980

2
1.998

2.020
2.016

V
V

Reference
VREF Voltage

IVREF = 0µA
IVREF = 500µA

VREF Pin Current Limit

VREF = 1.9V, Current Out of Pin

l

2

mA

LED Current Regulation
CTRL-Off Threshold (Falling)l200

CTRL-Off Rising Hysteresis

218

228

20
−100

mV
mV

CTRL Pin Current

VCTRL = 2V

Sense Voltage (VISP−VISN)(Analog Input)

VCTRL = 1.5V (100%), VIN = 36V, VISP = 24V
VCTRL = 750mV (50%), VIN = 36V, VISP = 24V
VCTRL = 300mV (5%), VIN = 36V, VISP = 24V

ISP Pin Current

VIN = 36V, VISP = 24V, VCTRL = 2V, Current Into Pin

50µA

ISN Pin Current

VIN = 36V, VISN = 23.9V, VCTRL = 2V, Current Into Pin

50µA

ISP/ISN Common Mode Range

VIN = 36V (Note 5)

Current Error Amplifier Transconductance

VIN = 36V, VISP = 24V

l
l
l

98.5
48.5
4

100
50
5

0

100

nA

101.5
51.5
6

mV
mV
mV

36
200

V
µA/V

Duty Cycle Control of LED Current
Sense Voltage (VISP−VISN)(Duty Cycle Input)

CTRL Duty = 75% (100%), VIN = 36V, VISP = 24V
CTRL Duty = 37.5% (50%), VIN = 36V, VISP = 24V
CTRL Duty = 15% (5%), VIN = 36V, VISP = 24V

99
49
4

CTRL Pulse Input High (VIH)

100
50
5

101
51
6

1.6

V

CTRL Pulse Input Low (VIL)
CTRL Pulse Input Frequency Range

mV
mV
mV

100

0.4

V

1000

kHz

1.012

V

Voltage Regulation
FB Regulation Voltage

VISP = VISN = 6V, VCTRL = 2V

FB Pin Current

VFB = 1V

l

0.988

1.000

−100

Voltage Error Amplifier Transconductance

100
480

nA
µA/V

Power Stage
Peak Current Limit

3.0

3.6

Minimum Off-Time(Note 6)55

Minimum On-Time(Note 6)

4.2

A
ns

55

ns

Bottom Switch On-Resistance90mΩ

Top Switch On-Resistance90mΩOscillator
Programmed Switching Frequency (fSW)

RT = 45.3k, VSYNC/SPRD = 0V
RT = 523k, VSYNC/SPRD = 0V

Spread Spectrum Frequency Range

RT = 45.3k, VSYNC/SPRD = 3.3V
RT = 523k, VSYNC/SPRD = 3.3V

RT Pin Current Limit

VRT = 0V, Current Out of Pin

l
l

1900
180
1900
180

2100
230

kHz
kHz

2650
290

kHz
kHz

34

SYNC/SPRD Threshold (Rising)

1.4

SYNC/SPRD Falling Hysteresis
SYNC/SPRD Pin Current

2000
200

µA
1.5

220
VSYNC/SPRD = 3.3V

−100

V
mV

100

nA

Soft-Start
SS Pin Charging Current

VSS = 0V

20

µA
Rev B

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3

LT3932/LT3932-1
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN/UVLO = 5V unless otherwise noted.
PARAMETERCONDITIONSSS Pin Discharging Current

VSS = 2V

MIN

TYP

MAX

UNITS

1.25

µA

SS Lower Threshold (Falling)

200

mV

SS Higher Threshold (Rising)

1.7

V

Fault Detection
Open-Circuit Threshold (FB Rising)l930

Open-Circuit Falling Hysteresis

950

970

55

Short-Circuit Threshold (FB Falling)l180

Short-Circuit Rising Hysteresis

200

mV
220

50

FAULT Pull-Down Current

VFAULT = 200mV, VFB = 0V

100

FAULT Leakage Current

VFAULT = 3.3V, VFB = 700mV

−100

mV
mV
mV
µA

100

nA

Overvoltage Protection
FB Overvoltage Threshold (FB Rising)

1.050

V

FB Overvoltage Falling Hysteresis

48

mV

LED Current Monitor
ISMON Voltage

VISP − VISN = 100mV (100%), VISP = 12V
VISP − VISN = 10mV (10%), VISP = 12V

0.965
80

1.000
100

1.030
120

V
mV

10

11

V

PWM Driver
PWMTG Gate Drive (VOUT – VPWMTG)

VOUT = 12V, VPWM = 2V

PWM Threshold (Rising)

VOUT = 12V, VRP = 0V

1.4

V

PWM Falling Hysteresis

VOUT = 12V, VRP = 0V

200

mV

PWM Pin Current

VPWM = 2V

PWM to PWMTG Propagation Delay
Turn-On
Turn-OffCPWMTG = 2.2nF (Connected from VOUT to PWMTG),
VOUT = 12V

l

−100

100
100
100

nA
ns
ns

Analog Control for PWM Dimming
PWM Voltage for 100% Dimming

RP = 28.7k, VREF = 2V

PWM Voltage for 0% Dimming

RP = 28.7k, VREF = 2V

PWM Dimming Accuracy

RP = 28.7k, VREF = 2V, VPWM = 1.1V
RP = 28.7k, VREF = 2V, VPWM = 1.9V

PWM Dimming Frequency

RP = 28.7k, RT = 45.3k, VSYNC/SPRD = 0V
RP = 332k, RT = 45.3k, VSYNC/SPRD = 0V

RP Pin Current Limit

VRP = 0V, Current Out of Pin

Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Do not apply a positive or negative voltage source to these pins,otherwise permanent damage may occur.
Note 3: The LT3932E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the −40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT3932I is guaranteed to meet performance specifications over the−40°C to 125°C operating junction temperature range. The LT3932H isguaranteed over the −40°C to 150°C operating junction temperature range.
Operating lifetime is derated for junction temperatures greater than 125°C.

4

2.00
l
l

V
0.99

V

7.8
87

10
90

12.4
93

%
%

7.42
116

7.81
122

8.20
128

kHz
Hz

60

µA

Note 4: This IC includes overtemperature protection that is intended toprotect the device during momentary overload conditions. The maximum
rated junction temperature will be exceeded when this protection is active.
Continuous operation above the specified absolute maximum operating
junction temperature may impair device reliability or permanently damage
the device.
Note 5: The current sense error amplifier is tested with VISP = 36V, andseparately, with VISN = 0V.
Note 6: The MIN on and off times are guaranteed by design and are nottested.

Rev B

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LT3932/LT3932-1
TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, unless otherwise noted.
EN/UVLO Pin Current

VIN UVLO Threshold (Rising)
3.6

1.3

5.1

3.4

1.2

1.1

1.0

VIN VOLTAGE (V)

5.5

EN/UVLO CURRENT (μA)

EN/UVLO VOLTAGE (V)EN/UVLO Threshold (Falling)
1.4

4.7

4.3

0

3.5
–50 –25

25 50 75 100 125 150
TEMPERATURE (°C)

03932 G01

2.6–50 –25

25 50 75 100 125 150
TEMPERATURE (°C)

VIN Shutdown Current
5.0

INTVCC Voltage

VIN Quiescent Current
3.5

3.5

INTVCC VOLTAGE (V)VIN CURRENT (mA)

VIN CURRENT (nA)

3.4

4.0

1

3.0
2.5
2.0
1.5
1.0

0.1

0

0
–50 –25

25 50 75 100 125 150
TEMPERATURE (°C)

VEN/UVLO = 1V
0

3.2
3.1
3.0

2.8
–50 –25

25 50 75 100 125 150
TEMPERATURE (°C)

INTVCC Load Regulation

VREF Voltage

2.02

2.02

3.36

2.01

2.01

2.00
1.99
1.98

3.30
3.28

2.03

VREF VOLTAGE (V)3.38
VREF VOLTAGE (V)

2.03

3.32

0

3

6

9
12
INTVCC CURRENT (mA)

15

25 50 75 100 125 150
TEMPERATURE (°C)
3932 G06

3.40

3.34

0

3932 G05

3932 G04

INTVCC VOLTAGE (V)

3.3

2.9

0.5

VEN/UVLO = 0.3V

0.01
–50 –25

25 50 75 100 125 150
TEMPERATURE (°C)
3932 G03

4.5
1k

10

0

3932 G02

10k

100

3.0

2.8

3.9

0.9
–50 –25

3.2

1.97–50 –25

VREF Load Regulation

2.00
1.99
1.98

0

25 50 75 100 125 150
TEMPERATURE (°C)
3932 G08

3932 G07

1.97

0

0.4

0.8
1.2
1.6
VREF CURRENT (mA)

23932 G09

Rev B

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5LT3932/LT3932-1
TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, unless otherwise noted.
INTVCC and VREF UVLO Threshold
3.3

2.02

3.0

MINIMUM OFF–TIMEMINIMUM ON–TIME

65

150°C
2.00

25°C

1.99

2.4

TIME (ns)

2.01

2.1

1.98

6

12
18
24
VIN VOLTAGE (V)

45

35

1.5
0

55

1.8

–50°C

1.97

Minimum On-Time and Off-Time75

2.7
VOLTAGE (V)

VREF VOLTAGE (V)

VREF Line Regulation
2.03

30

1.2
–50 –25

36

INTVCCVREF
025–50 –25

25 50 75 100 125 150
TEMPERATURE (°C)

3932 G10

025 50 75 100 125 150
TEMPERATURE (°C)

3932 G11

3932 G12

SS Thresholds

SS Pin Pull-Up Current

RP and RT Pin Current Limit
70

2.0

24
23

1.6

50

40

SS VOLTAGE (V)22
SS CURRENT (µA)

CURRENT (µA)

60

21
20
19
18

30

20
–50 –25

0.8

0.4

16
–50 –25

25 50 75 100 125 150
TEMPERATURE (°C)

00–50 –25

25 50 75 100 125 150
TEMPERATURE (°C)

3932 G13PWM Duty Ratio

220
RT = 523k
200

1600

110

INTERNAL PWM
RT = 45.3k

100
90
80
DUY RATIO (%)

240

PWM FREQUENCY (kHz)RT = 45.3k

1800

25 50 75 100 125 150
TEMPERATURE (°C)
3932 G15Internal PWM Frequency
10

260

2000

0

3932 G14

SW Frequency
2200

SW FREQUENCY (kHz)LOWER RISING
LOWER FALLINGUPPER RISING
UPPER FALLING

17

RP Current
RT Current
0

1.2

1

70
60
50
40
30
20
10

1400
–50 –25180
0
25 50 75 100 125 150
TEMPERATURE (°C)
3932 G16

6

0.1
10k

0

EXTERNAL PWM
100k
RP RESISTANCE (Ω)

1M
3932 G17

–10

0

0.5

1
1.5
2
PWM VOLTAGE (V)2.5

33932 G18

Rev B

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LT3932/LT3932-1
TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, unless otherwise noted.
LED Current (Digital CTRL)
100

90

90

80

80

70

70

VISP - VISN (mV)

100

VISP - VISN (mV)

110

60
50
40
30

50
40
30
20

10

10

0

0
0

0.25 0.50 0.75 1 1.25 1.50 1.75
CTRL VOLTAGE (V)

–10

2

0

240

180
150
120
90

150
120
90

30

30
0
4.8

99.6 100.0 100.4 100.8 101.2
VISP - VISN (mV)

4.93932 G22

5.3

49.6

30

50
70
DUTY RATIO (%)

0.5

903932 G25

51.0

2 LEDs (APPROX. 6V)
2MHz SW FREQUENCYVCTRL = 735mV

49.2

48.8

48.0

0

50

3932 G23

48.4

2.4

10

1.0

0

5.4

6

12
18
24
VIN VOLTAGE (V)30

363932 G26250

300
3932 G24

LED Current vs VOUT

50.2

49.8

49.4

0

100
150
200
VISP – VISN (mV)

50.6
VISP - VISN (mV)

3.6
VISP - VISN (mV)PEAK SW CURRENT (A)

50.0

2.0

5
5.1
5.2
VISP - VISN (mV)

1.02

1.5

LED Current Line Regulation

Peak SW Current Limit
4.0

2.8

1.01

2.0

300 UNITS
VCTRL = 300mV

180

60

3.2

0.99
1
FB VOLTAGE (V)ISMON Voltage

210

60

99.2

0.98

3932 G21

ISMON VOLTAGE (V)

210

0
98.8

155°C
25°C
–50°C

270

NUMBER OF UNITSNUMBER OF UNITS

240

0
0.97

12.5 25 37.5 50 62.5 75 87.5 100
CTRL DUTY RATIO (%)

LED Current (5% Regulation)
300

300 UNITS
VCTRL = 1.5V

155°C
25°C
–50°C

50

3932 G20

LED Current (100% Regulation)
270

75

25

3932 G19300

VCTRL = 2V

100

60

20

–10

LED Voltage Limit
125

VISP – VISN (mV)

LED Current (Analog CTRL)
110

49.0

VIN = 36VVCTRL = 750mV
2MHz SW FREQUENCY
0

6

12
18
24
VOUT VOLTAGE (V)30

363932 G27

Rev B

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7

LT3932/LT3932-1
TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, unless otherwise noted.
FB OPENLED Threshold
RISINGFALLING

1.05

FB SHORTLED Threshold

1.00
0.95
0.90

Power Switch On-Resistance300

RISINGFALLING

0.35
FB VOLTAGE (V)FB VOLTAGE (V)

0.40

0.30
0.25
0.20
0.15

0.85
0.80
–50 –250

25 50 75 100 125 150
TEMPERATURE (°C)

0.10
–50 –25

0

2 LEDs (APPROX. 6V, 1A)
20
25
30
VIN VOLTAGE (V)35

40

5 LEDs (APPROX. 15V)
4 LEDs (APPROX. 12V)

1.01

PWMTG Voltage

0

400

800
1200
ILED (mA)

1600

0.97
–50 –25

2000

10

9

8
VOUT = 20V
VPWM = 2V
25 50 75 100 125 150
TEMPERATURE (°C)

025 50 75 100 125 150
TEMPERATURE (°C)
3932 G33FB OVLO Threshold
1.100

TURN–ON
TURN–OFFRISINGFALLING

1.050

200
175
150
125

1.000

0.950

100
CPWMTG = 2.2nF (X7R)
DATA INCLUDES CAPACITANCE
VARIATION WITH TEMPERATURE

75
50–50 –25

VCTRL = 2V
VISP – VISN = 0V

3932 G32

FB VOLTAGE (V)PROPAGATION DELAY (ns)

11

0

0.99

PWM Driver Propagation Delay
250
225

7
–50 –25

1.00

0.98
VIN = 24V
2MHz SW FREQUENCY

3932 G31

12

VOUT – VPWMTG (V)Regulated FB Voltage

90

80

25 50 75 100 125 150
TEMPERATURE (°C)

1.02

85

15

0

3932 G30

FB VOLTAGE (V)EFFICIENCY (%)

EFFICIENCY (%)

90

85

0

25 50 75 100 125 150
TEMPERATURE (°C)
3932 G35

3932 G34

8

0–50 –25

25 50 75 100 125 150
TEMPERATURE (°C)

95

95

10

100

Efficiency vs ILED
100

400kHz
2MHz

5

150

3932 G29

Efficiency vs VIN

80

200

50

3932 G28

100

TOP SWITCH
BOTTOM SWITCH250
RESISTANCE (mOhm)

1.10

0.900
–50 –250

25 50 75 100 125 150
TEMPERATURE (°C)
3932 G36

Rev B

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LT3932/LT3932-1
TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, unless otherwise noted.
C/10 Threshold
RISINGFALLING

16
14

SW CURRENT (A)VISP - VISN (mV)DA Current Limit

12
10

200

2.4

160

2.3

2.2

2.1

8
6
–50 –250

25 50 75 100 125 150
TEMPERATURE (°C)

2.0
–50 –25

NUMBER OF UNITS

120

80

0

25 50 75 100 125 150
TEMPERATURE (°C)

0
8.6

9

9.4 9.8 10.2 10.6 11.0 11.4 11.8
PWM DUTY RATIO (%)

3932 G38

Internal PWM Duty Ratio (90%)

160

250 UNITS
VPWM = 1.1V

150°C
25°C
–50°C

40

3932 G37

200

Internal PWM Duty Ratio (10%)

2.5

NUMBER OF UNITS

183932 G39

Input Voltage Transient Response

Input Voltage Transient Response

250 UNITS
VPWM = 1.9V

150°C
25°C
–50°C

VIN
10V/DIV

VIN
10V/DIVILED
100mA/DIV

ILED
100mA/DIV

120

80

40

1ms/DIV088.6 89 89.4 89.8 90.2 90.6 91.0 91.4 91.8
PWM DUTY RATIO (%)

3932 G41

1ms/DIV

3932 G42

FRONT PAGE APPLICATION
15V TO 25V INPUT VOLTAGE STEP
3 LEDs (APPROX. 9V)

FRONT PAGE APPLICATION
25V TO 15V INPUT VOLTAGE STEP
3 LEDs (APPROX. 9V)

Start-Up with 10% Internal PWM

Start-Up with 90% Internal PWM

3932 G40

Turn-On and Turn-Off
VIN
20V/DIV

VIN
20V/DIV

VIN
20V/DIV

VOUT
5V/DIV

VOUT
5V/DIV

VOUT
5V/DIVILED
500mA/DIV

ILED
500mA/DIV

ILED
500mA/DIV

5ms/DIVFRONT PAGE APPLICATION
3 LEDs (APPROX. 9V)

3932 G43

5ms/DIV

3932 G44

FRONT PAGE APPLICATION WITH PWM = 1.1V
3 LEDs (APPROX. 9V)

5ms/DIV

3932 G45

FRONT PAGE APPLICATION WITH PWM = 1.9V
3 LEDs (APPROX. 9V)

Rev B

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9LT3932/LT3932-1
PIN FUNCTIONS
VIN: Input Voltage Pins. These pins supply power to theinternal, high performance analog circuitry, and they supply the inductor current when the internal high side powerswitch is on. Connect capacitors between these pins and
GND and see Selecting and Placing the Input Capacitors
in Applications Information for advice regarding theirplacement.
EN/UVLO: Enable and Undervoltage Lockout Pin. A voltage at this pin greater than 1.15V will enable switching,
and a voltage less than 300mV is guaranteed to shut down
the internal current bias and sub-regulators. A resistor
network between this pin and VIN can be used to set thepin voltage and automatically lockout the part when VIN isbelow a certain level. No internal components pull up or
down on this pin, so it requires an external voltage bias
for normal operation. This pin may be tied directly to VIN.
INTVCC: Internally Regulated, Low-Voltage Supply Pin.
This pin provides the power for the converter switch gate
drivers. Do not force any voltage on this pin, but bypass
it with a 2.2µF capacitor to GND.

VREF: Reference Voltage Pin. This pin provides a buffered
2V reference capable of 1mA drive. It can be used to supply resistor networks for setting the voltages at the CTRL
and PWM pins. Bypass with a 2.2μF capacitor to GND.
FB: Feedback Pin. When the voltage at this pin is near 1V,
the regulated current is automatically reduced from theprogrammed value. A resistor network between this pin
and VOUT can be used to set a limit for the output voltage.
If the voltage at the FB pin reaches 1.05V, an overvoltage
lockout comparator disables switching.
FAULT: Fault Pin. Connect to INTVCC through a resistanceof 100k. When the FB pin voltage is less than 200mV, aninternal switch pulls this pin low to indicate a short-circuit.
When FB is greater than 950mV and the voltage between
ISP and ISN is simultaneously less than 10mV, the switch
pulls this pin low to indicate an open-circuit.

ISP: Positive Current Sense Pin. This pin is one of the
inputs to the internal current sense error amplifier. It
should be connected to the positive side of the externalsense resistor.

SS: Soft-Start Pin. At startup and recovery from fault conditions, a 20μA current charges the capacitor and the FB
voltage tracks the rising voltage at this pin until the load
current reaches its programmed level. Typical values forthe capacitor are 10nF to 100nF. A resistor from SS to
INTVCC is used to select one of several fault modes. See
Soft-Start and Fault Modes in Applications Information
for more details.

ISN: Negative Current Sense Pin. This pin is one of the
inputs to the internal current sense error amplifier. It
should be connected to the negative side of the externalsense resistor.

VC: Compensation Pin. A capacitor connected from thispin to GND stabilizes the current and voltage regulation.
See Stabilizing the Regulation Loop in the Applications
Information section for more details.

ISMON: Output Current Monitoring Pin. This pin provides
a buffered voltage output equal to 10mV for every 1mV
between ISP and ISN.

SW: Switch Pins. These two pins are internally connectedto the power devices and drivers. They should always betied together. In normal operation, the voltage of thesepins will switch between the input voltage and zero at
the programmed frequency. Do not force any voltage onthese pins.

CTRL: Control Pin. An analog voltage from 250mV to
1.25V at this pin programs the regulated voltage between
ISP and ISN (and therefore, the regulated current supplied
to the load). Alternatively, a digital pulse at this pin withduty cycle from 12.5% to 62.5% can be used to program the regulated voltage. Below 200mV or 10% duty
cycle, the CTRL pin voltage disables switching. For moredetail, see Regulated LED Current in Typical Performance
Curves and Programming LED Current with the CTRL Pin
in Applications Information.

10

RT: Timing Resistor Pin. A resistor from this pin to GND
programs the switching frequency between 200kHz and2MHz. Do not leave this pin open.

Rev B

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LT3932/LT3932-1
PIN FUNCTIONSSYNC/SPRD: Synchronization Pin. To override the programmed switching frequency, drive this pin with an
external clock having a frequency between 200kHz and2MHz. Even when using the external clock, select an RT
resistor that corresponds to the desired switching frequency. Tie the pin to INTVCC to enable spread spectrum
frequency modulation. This pin should be tied to GND
when not in use.
BST: Boost Pin. This pin supplies the high side powerswitch driver. Connect a 22nF capacitor between thispin and SW, and connect a diode from INTVCC to BST tocharge the capacitor when the SW pin is low.
PWM: PWM Input Pin. With the RP pin tied to GND, drive
this pin with a digital pulse to control PWM dimming of
the LEDs. Alternatively, set the voltage of this pin between
1V and 2V to generate an internal pulse with duty ratio
between 0% and 100%. In this case, place a 1µF bypass
capacitor between this pin and GND. Tie this pin highwhen PWM dimming is not required.

PWMTG: PWM Driver Output Pin. This pin can drive thegate of an external, high side PMOS device for PWM dimming of LEDs. Do not force any voltage on this pin.
RP: PWM Resistor Pin. Connect a resistor from this pin to
GND to set the frequency of the internal PWM signal. Do
not use a resistor larger than 1MΩ. If using an external
PWM pulse for LED dimming, tie this pin to GND.
VOUT: PWM Driver Supply Pin. This pin supplies an internal regulator for the driver of the external PMOS device.
Tie this pin to the output voltage even if dimming is not
required.
GND: Ground Pins. These must be soldered to the groundplane of the circuit board.

Rev B

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11

LT3932/LT3932-1
BLOCK DIAGRAM
D1
CVCC
25
26
REN2

24

INTVCC

VIN
CIN

VIN

INTERNAL VCC
REGULATORAND UVLO

EN/UVLO
27

20

21

R

VREF
2V REFERENCE

Q

SW
18

SYNCHRONOUS
CONTROLLERPEAK CURRENTCOMPARATOR

19
BOTTOM SWITCHDRIVERDA CURRENT

+
–
+

LIMIT

8.2µH

RT

VOUT

10
RT

CIN
VIN

TOP SWITCHDRIVER

S

1

17

22nF

REN1

CREF

16

BST

1.4V
SYNC/SPRD
11

14200kHz TO
2MHz
OSCILLATOR

–

4.7µF

+

S/H

VOUT – 10V
REGULATOR

S/H

50mΩ

CURRENTREGULATIONAMPLIFIER
gm = 200µS

PWMTG
PWMTG
DRIVER

13

–
+

3k

–

A/D
DETECTOR+CONTROL
BUFFER

+
+
–

+

CTRL
28

–

1.25V

PWM
12

3k

ISMON

INTERNAL
PWM SIGNAL

7

30k
250mV

+

–

10x
VOLTAGEREGULATIONAMPLIFIER
gm = 480µS

ISN
6
ISP

+
+
–

5

4

1.0V
950mV
20µA

INTVCC––

1.25µA
200mV
GND

15

22

23

29

SS

VC

2

3
RSS
CSS

12

RFB1

RFAULT

FAULT

+
FAULT
LOGIC

RFB2

FB

8
FAULT
COMPARATORS

FAULT
LOGIC

+

RP
9

3923 BDINTVCCCC

Rev B

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LT3932/LT3932-1
OPERATION
The LT3932 is a step-down LED driver that utilizes fixedfrequency, peak-current control to accurately regulate thecurrent through a string of LEDs. It includes two powerswitches and their drivers. The switches connect an external inductor at the SW pin alternately to the input supply and then to ground. The inductor current rises andfalls accordingly and the peak current can be regulated
by adjusting the duty ratio of the power switches throughthe combined effect of the other circuit blocks.
The synchronous controller ensures the power switches
do not conduct at the same time, and a programmableoscillator turns on the top switch at the beginning of eachswitching cycle. The frequency of this oscillator is set by
an external resistor at the RT pin and can be overridden byexternal pulses at the SYNC/SPRD pin. The SYNC/SPRD
pin can also be used to command spread spectrum frequency modulation (SSFM), which reduces radiated andconducted electromagnetic interference (EMI).
The top switch is turned off by the peak current comparator which waits during the on-time for the increasing
inductor current to exceed the target set by the voltage
at the VC pin. This target is modified by a signal from theoscillator which stabilizes the inductor current. A capacitor at the VC pin is necessary to stabilize this regulation
loop.
The target for the inductor current is derived from thedesired LED current programmed by the voltage at the
CTRL pin. The analog-to-digital detector and the control buffer convert either a DC voltage or digital pulses
at the CTRL pin into the input for the current regulation

amplifier. The other input to this amplifier comes from the
ISP and ISN pin voltages. An external current sense resistor between these pins should be placed in series with thestring of LEDs such that the voltage across it provides the
feedback to regulate the LED current. The current regulation amplifier then compares the actual LED current to theprogrammed LED current and adjusts VC as necessary.
The voltage regulation amplifier overrides the current regulation amplifier, when the FB pin voltage approaches aninternal 1V reference. An external resistor network fromthe LED string to the FB pin provides an indication of the
LED string voltage and allows the voltage amplifier toprevent overvoltage of the LED string.
The FB voltage is also monitored to detect fault conditions
like open and short-circuits, which are then reported bypulling the FAULT pin low. The response to a fault can beselected either to try hiccup restarts or to latch-off by the
choice of an external resistor connected to the SS pin.
Refer to Applications Information for a detailed explanation of fault responses.
Finally, pulse-width-modulation (PWM) of the LED current is achieved by turning on and off an external PMOS
switch between the inductor and the string of LEDs. An
external pulse at the PWM pin controls the state of thePWM driver, or a DC voltage at the PWM pin dictates theduty ratio of an internal PWM pulse, whose frequency is
programmed by an external resistor at the RP pin. Aftereach pulse, when the PMOS switch is open, the LT3932
preserves the voltages of the capacitors at VC and VOUT
to ensure a rapid recovery for the next pulse.

Rev B

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13

LT3932/LT3932-1
APPLICATIONS INFORMATION
The following is a guide to selecting the external components and configuring the LT3932 according to therequirements of an application.
Programming LED Current with the CTRL Pin
The primary function of the LT3932 is to regulate the current for a string of LEDs. This current should pass througha series current sense resistor that can be placed anywhere in the string. Then the voltage across this resistor
will be sensed by the current regulation amplifier throughthe ISP and ISN pins and regulated to a level programmedby the CTRL pin. The maximum resistor voltage that canbe programmed is 100mV, which corresponds to 2A
through the LED string when a 50mΩ current sense resistor is used.

Additionally, the LT3932 is capable of interpreting apulse at the CTRL pin. The high level of the pulse must
be greater than 1.6V. The low level must be less than
400mV. The frequency must be greater than 100kHz andless than 1MHz. Then the regulated voltage between ISP
and ISN will vary with the duty ratio of the pulse as shownin Figure 2.
In this case, the LED current is zero for duty ratios lessthan 12.5% and reaches its maximum above 62.5%. The
LT3932 will cease switching if the duty ratio of the CTRL
pin pulse is less than 10%, and also for DC CTRL pin
voltages less than 200mV.
ILED
100mV
RSNS

To allow for this maximum current, the CTRL pin may
be connected directly to the VREF pin, which provides
an accurate 2V reference. Lower current levels can be

DCTRL < 10%
CTRL–OFF

50mV
RSNS
ILED
100mV
RSNS

VCTRL < 200mVCTRL–OFF

0

12.5%

37.5%

62.5% 75%

DCTRL
3932 F02

50mV
RSNS

Figure 2. Duty Ratio CTRL Range

0

0.25V

0.75V

1.25V 1.5V

VCTRL
3932 F01

To reduce the LED current when the temperature of theLEDs rises, use resistors with negative temperature coefficient (NTC) in the network from VREF to CTRL as shownin Figure 3.

Figure 1. Analog CTRL Range

programmed by DC CTRL voltages between 250mV and
1.25V as shown in Figure 1.
Below 250mV, the CTRL pin commands zero LED current,
and above 1.25V, it commands the maximum. When an
independent voltage source is not available, the intermediate CTRL voltages may be derived from the 2V referenceat the VREF pin using a resistor network or potentiometeras long as the total current drawn from the VREF pin isless than 1mA.

14

VREF

VREF
RCTRL1

LT3932RCTRL1RNTCRCTRL2

LT3932CTRL

CTRL
RCTRL23932 F03

RNTC

Figure 3. Setting CTRL with NTC Resistors

Rev B

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LT3932/LT3932-1
APPLICATIONS INFORMATION
Setting Switching Frequency with the RT Pin

100

The switching frequency of the LT3932 is programmed bya resistor connected between the RT pin and GND. Valuesof the RT resistor from 45.3k up to 523k program frequencies from 2MHz down to 200kHz as shown in Table 1.
Higher frequencies allow for smaller external components
but increase switching power losses and radiated EMI.

80
AMPLITUDE (dBuV)

60
40
20
0
–20

Table 1. RT Resistance Range
SWITCHING FREQUENCY

RT

2.0MHz45.3k

1.6MHz59.0k

1.2MHz80.6k

1.0MHz97.6k

750kHz133k

500kHz205k

400kHz255k

300kHz348k

200kHz523k–40

WITH SSFMWITHOUT SSFM
1

3

5
7
FREQUENCY (MHz)9113932 F04

Figure 4. Typical Average Conducted Emissions

The attenuation varies depending on the chosen switchingfrequency, the range of frequencies in which interferenceis measured, and whether a test measures peak, quasipeak, or average emissions. The results of several othersuch emission measurements are with select TypicalApplications.

Synchronizing Switching Frequency

Understanding the Current Limit

The switching frequency can also be synchronized to an
external clock connected to the SYNC/SPRD pin. The highlevel of the external clock must be at least 1.4V, and thefrequency must be between 200kHz and 2MHz. The RT
resistor is still required in this case, and the resistanceshould correspond to the frequency of the external clock.
If the external clock ever stops, the LT3932 will rely on
the RT resistor to set the frequency.

The choice of switching frequency should be made knowing that, although the maximum LED current that can be
programmed with the CTRL pin is 2A, the inductor current
may exceed 2A when the frequency is high and the output
voltage is low as in a short-circuit. This is because there
is a minimum on-time for which the SW pin will be driven
high during each switching period. The inductor current
increases during this time, and if the frequency is high andthe output voltage low, there may not be enough off-timeremaining in each switching period for the inductor current to decrease back to the level at which it started. In thiscase, the net inductor current would increase with eachswitching period regardless of the state of the CTRL pin.

Enabling Spread Spectrum Frequency Modulation
Connecting SYNC/SPRD to INTVCC will enable spread
spectrum frequency modulation (SSFM). The switchingfrequency will vary from the frequency set by the RT resistor to 125% of that frequency. If neither synchronizationnor SSFM is required, connect SYNC/SPRD to GND.
As shown in Figure 4, enabling SSFM can significantly attenuate the electromagnetic interference that
the LT3932, like all switching regulators, emits at theswitching frequency and its harmonics. This feature isdesigned to help devices that include the LT3932 performbetter in the various standard industrial tests related tointerference.

To prevent large inductor currents that would damage theLT3932, the high-side switch is not turned on until the
inductor current decreases to less than the DA current
limit, which is approximately 2.3A. While the high-side
switch is off, the current is sensed through the low-side
switch. The peak inductor current may increase to 3.6A,
but the off-time and the switching period are extended
until the inductor current reaches equilibrium as shownin Figure 5.
Rev B

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15

LT3932/LT3932-1
APPLICATIONS INFORMATION
Selecting an Output Capacitor
DA CURRENT LIMITOUTPUT SHORTEDINDUCTORCURRENT
500mA/DIV
100µs/DIV

3932 F05

Figure 5. Extended Off-Time at Current Limit

The DA current limit is relevant only when the output
capacitor is shorted to GND. When instead the LED stringis shorted to GND, the voltage across the external PMOS
(described later) is high enough that the required on-time
is greater than the minimum on-time. This means that, inspite of a shorted LED string, the inductor current remains
in regulation even at the highest switching frequency.

The inductor must be rated for the current limit regardlessof the intended application. Its value, in most applications,should be selected such that the inductor current ripple is
not more than 25% of the maximum output current. Whenthat current is 2A, for example, the minimum inductancecan be calculated using the following equation:
VOUT

VIN(MAX)•

VIN(MAX) – VOUT 1MHz
•
fSW
1V

However, for high output voltages even the above equation
would suggest an inductance value that is too small. For
stability, the LT3932 requires an inductance greater than:L = 1µH •VOUT 1MHz•
1V
fSW

Choose the larger of the values given by these equations.
The manufacturers featured in Table 2 are recommended
sources of inductors.
Table 2. Inductor Manufacturers
MANUFACTURERWEBSITE

Würth Elektronik

www.we-online.com

Coilcraftwww.coilcraft.com

16

COUT = 100µF •1V 1MHz•VOUT fSW

However, applications may still be stable with more orless capacitance, and more capacitance may improve LED
current waveforms for large PWM dimming ratios.
Use X7R or X5R ceramic capacitors as they retain theircapacitance better than other capacitor types over a widevoltage and temperature range. Sources of quality ceramicand electrolytic capacitors are listed in Table 3.
Table 3. Capacitor Manufacturers

Selecting an Inductor

L = 2µH •Some applications are sensitive to ripple current in the
LED string. In those cases, a capacitor at the output will
absorb part of the inductor current ripple and thereby
reduce the LED current ripple. Typically, the value of thiscapacitance is inversely proportional to the switching frequency and the output voltage as shown below:

MANUFACTURERWEBSITE

Murata Manufacturingwww.murata.com

Garrett Electronics

www.garrettelec.com

AVX

www.avx.com

Nippon Chemi-Con

www.chemi-con.co.jp/eStabilizing the Regulation Loop
Stabilizing the regulation loop typically requires only acapacitor CC connected from the VC pin to GND. For mostdesigns, values between 1nF and 10nF are suitable. Whenusing an output capacitor COUT larger than 10µF, as isneeded for large PWM dimming ratios, a resistor RC inseries with CC may be necessary. Larger values of COUT
require larger values of RC. See Typical Applications forsome examples.
Selecting and Placing the Input Capacitors
Although they do not impact stability, several capacitors
are necessary between VIN and GND to properly bypass
the input supply voltage. At least 10μF is required in
total, although it does not have to be composed entirelyof ceramic capacitors placed very close to the VIN pins.
However, it is important that a ceramic capacitor be placed
Rev B

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LT3932/LT3932-1
APPLICATIONS INFORMATION
as close as possible to each of the pairs of VIN pins (Pins
16 and 17 as well as 20 and 21) and their adjacent GND
pins as shown in Figure 6. These two capacitors should be
at least 1μF if possible. Because the SW pins lie between
the VIN pins, it is convenient to join the VIN pins using a
trace on the second layer of the circuit board.
Another 1μF capacitor should be placed very close to theremaining VIN pin (Pin 26), which supplies the internal
control circuitry.

8

7

6

5

4

3

2

1

9

28

10

27

11

26

29

12

GND
VIN

25

13

24

14

23
15 16 17 18 19 20 21 22

1µF
CERAMIC
GND

1µF

VIN

VIN

GND

1µF
CERAMIC
GND

100nF
BST
SW

TOP LAYER

3932 F06

BOTTOM LAYER

Figure 6. Placement of Input Capacitors

Selecting a MOSFET for PWM Dimming
Pulse-Width-Modulation (PWM) dimming of the LED current is an effective way to control the brightness of thelight without varying its color. The brightness can also be
adjusted more accurately this way than by varying thecurrent level.
The LT3932 features a PWMTG driver that is intended
for a high-voltage PMOS switch in position to effectively
PWM dim a string of LEDs from the output capacitor andcurrent sense resistor. When the switch is open and thestring is disconnected, the LED current will be zero. In

contrast to a low-side NMOS driver, this feature eliminates
the need for a dedicated return path for the LED current
in automotive applications or other grounded chassis
systems.
The gate driver for this PMOS draws power through the
VOUT pin, which must be connected even in applications
that do not require PWM dimming. When the PWM pin
voltage is greater than 1.4V, the driver will pull the gateof the PMOS to a maximum of 10V below the VOUT pin. If
VOUT is below 10V, the gate drive is necessarily reduced.
For constant current applications, leave PWMTG open,
connect the load directly after the current sense resistor,and connect PWM to INTVCC. In these cases, analog dimming may be implemented with the CTRL pin.
The drain-source voltage rating of the chosen PMOS
should be greater than the maximum output voltage.
Typically the output voltage is a little higher than the sumof the forward voltages of the LEDs in the string. However,when the string is broken, the output voltage will begin
to increase due to the imbalance of inductor current andload current. As described in detail later, the LT3932 will
not reduce the inductor current nor limit the output voltage until the FB pin voltage approaches 1V. Therefore, themaximum output voltage is ultimately determined by theresistor network between FB and VOUT.
In most applications, the gate-source voltage rating of
the PMOS should be at least 10V. The only exceptions
to this rule are applications for which the output voltage
is always less than 10V. The PWMTG driver will try topull the gate of the PMOS down to 10V below VOUT, but
it cannot pull the gate below GND. Therefore, when the
maximum output voltage is less than 10V, the PMOS gate
source voltage rating will be sufficient if it is merely equal
to or greater than the output voltage.
Finally, the drain current rating of the PMOS must exceed
the programmed LED current. Assuming this condition
and the conditions above are met, the only electricalparameter to be considered is the on-resistance. Other
parameters such as gate charge are less importantbecause PWM dimming frequencies are typically too low
for efficiency to be affected noticeably by gate charging
loss or transition loss.
Rev B

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17

LT3932/LT3932-1
APPLICATIONS INFORMATION
Table 4 lists recommended manufacturers of PMOS
devices.
Table 4. PMOS Manufacturers
MANUFACTURERWEBSITE

Infineon

www.infineon.com

Vishay Intertechnology

www.vishay.com

NXP Semiconductors

www.nxp.com

Selecting an RP Resistor for Internal PWM Dimming
If the RP pin is tied to GND, an external pulse-width modulated signal at the PWM pin will control PWM dimmingof the LED load. The signal will enable the PWMTG driverand turn on the external PMOS device when it is higher
than 1.4V.
However, the LT3932 is capable of PWM dimming evenwhen an external PWM signal is not available. In this case,an internal PWM signal with frequency set by a resistor at
the RP pin and duty ratio set by a DC voltage at the PWM
pin will control the PWMTG driver. The RP resistor should
be one of the seven values listed in Table 5. For each ofthese values, the PWM frequency is a unique ratio of theswitching frequency.
Table 5. Internal PWM Dimming Frequencies
RP
28.7k
47.5k
76.8k
118k
169k
237k
332k

2MHz
7.81kHz
3.91kHz1.95kHz
977Hz
488Hz
244Hz
122Hz

SWITCHING FREQUENCY
1MHz
500KHz3.91kHz1.95kHz1.95kHz
977Hz
977Hz
488Hz
488Hz
244Hz
244Hz
122Hz
122Hz
61Hz
61Hz
31Hz

250KHz
977Hz
488Hz
244Hz
122Hz
61Hz
31Hz
15Hz

When using the internal PWM signal, set the voltage at
the PWM pin between 1V and 2V. The PWMTG driver will
stay off if PWM is below 1V, and it will stay on if PWM
is above 2V. Between 1V and 2V there are 128 evenly
spaced thresholds corresponding to 128 discrete PWM
duty ratios from 0% to 100%. This range of 1V to 2V has
been chosen so that the PWM voltage may be set using
a potentiometer or a resistor network and the 2V reference available at the VREF pin. Place a small 1µF ceramic
capacitor near the PWM pin to ground.

18

There are a couple of exceptions to the PWM dimming
behavior described above. First, once initiated, the PWM
on-time will will last at least four switching cycles regardless of the signal at the PWM pin and the resistor at theRP pin. This ensures that the current regulation loop hasenough time to reach equilibrium but still allows for a
5000:1 dimming ratio when the PWM frequency is 100Hz
and the switching frequency is 2MHz. The LT3932-1 does
not enforce this four-cycle limit so that dimming ratiosof 10000:1 or greater are possible in some applications.
Second, to avoid excessive start-up times, after the first
PWM pulse, PWMTG will stay on until the SS pin voltage
reaches 1.7V or the LED current has reached 10% of the
full-scale current.
PWM Dimming with Very Long Off Times
To enhance PWM dimming, the VOUT and VC pin voltages
are driven when the PWM pulse (internal or external) is
at a logic low to maintain the charge on the capacitors at
those pins. Consequently, when PWM returns to a logic
high state, the LED current can quickly reach the regulated
level even if PWM was low for a very long time. This feature facilitates machine vision applications which require
a synchronized strobe light or brief illuminating flashes
on short delay.
Monitoring LED Current
The ISMON pin provides an amplified and buffered monitor of the voltage between the ISP and ISN pins. The
gain of the internal amplifier is ten, and the speed is fastenough to track the pulse-width modulated LED current.
However, as shown in Figure 7, the ISMON voltage can befiltered with a resistor-capacitor network to monitor the
average LED current instead.
LT3932
ISMON

RMON
CMON
3932 F07

Figure 7. ISMON Filter Configuration

Rev B

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LT3932/LT3932-1
APPLICATIONS INFORMATIONThe resistor should be 1MΩ. The capacitance can be aslarge or small as needed without affecting the stability of
the internal amplifier. For example, when the PWM frequency is 200Hz, a 100nF capacitor combined with the
1MΩ resistor would limit the ripple on ISMON to 1%.
VOUT
LT3932

RFB2
FB
RFB1


R 
VOUT(MAX) = 1V •  1+ FB2 
RFB1 


3932 F08

Figure 8. FB Resistor Configuration

Selecting the FB Resistors
Two resistors should be selected to form a network
between the output voltage and the FB pin as shown in
Figure 8.
This network forms part of a voltage regulation loop when
FB is nearly 1V. In this case, the LT3932 will override
the programmed LED current to lower the output voltage
and limit FB to 1V. This resistor configuration therefore
determines the maximum output voltage.
Note that this voltage limit may be reached inadvertently
if it is set too close to the typical output voltage and theoutput capacitor is too small. To avoid interference withthe current regulation, the feedback resistors should bechosen such that FB is about 700mV when the LEDs are
conducting.
For a 12V string of LEDs, design for a maximum output
voltage of about 17V. Start with a 10k resistor for RFB1.
To calculate the value of RFB2, add 10k for every volt ofdifference between FB (1V) and the maximum output voltage. In this case, the nearest standard 1% value for RFB2
would be 162k.
In this way, the LT3932 can also be configured as a voltage regulator instead of an LED driver. It will regulate theoutput voltage near the programmed maximum as long as
the load current is less than the current level programmedby CTRL.

Understanding FB Overvoltage Lockout
It is possible that the FB voltage can exceed the 1V limit.
If the output voltage is near the maximum when the LED
string opens, it may take too long for the feedback loop
to adjust the inductor current and avoid overcharging
the output. However, if the FB voltage exceeds the 1.05V
Overvoltage Lockout Threshold, the LT3932 will immediately stop switching and resume only when FB decreases
to 1V.
This threshold may be routinely exceeded when theLT3932 is being operated as a voltage regulator and theload current decreases rapidly. In this case, the pause inswitching limits the output overshoot and ensures that thevoltage is back in regulation as quickly as possible. For
safe operation, choose RFB2 and RFB1 values to ensure
the output voltage is not greater than VIN when the FB
voltage is 1.05V.
Open and Shorted LED Fault Detection and Response
The resistor network formed by RFB1 and RFB2 also defines
the criteria for two fault conditions with respect to the LED
string: short and open-circuits. For the LT3932, a shortcircuit is when FB is less than 200mV. An open-circuit
is when FB is greater than 950mV and simultaneously
the difference between ISP and ISN is less than 10mV(the C/10 threshold). The latter condition ensures that theoutput current is low (as it should be in an open-circuit)
not just that output voltage is high as it may be when theLEDs are conducting a large current.
In both cases, a fault is indicated by an internal device
pulling the voltage at the FAULT pin low. There is nothinginternal that pulls this voltage high, so an external resistor between INTVCC and FAULT is necessary as shown in
Figure 9. This configuration allows multiple FAULT pins
and similar pins on other parts to be connected and sharea single resistor.
INTVCCRFAULT

LT3932
FAULT
3932 F09

Figure 9. FAULT Resistor Configuration
Rev B

For more information www.analog.com

19

LT3932/LT3932-1
APPLICATIONS INFORMATION
Soft-Start and Fault Modes
The SS pin has two functions. First, it allows the user toprogram the output voltage startup ramp rate. An internal
20μA current pulls up the SS pin to INTVCC. Connecting
an external capacitor CSS from the SS pin to GND, as
shown in Figure 10, will generate a linear ramp voltage.
The LT3932 regulates the FB pin voltage to track the SS
pin voltage until VOUT is high enough to drive the LED at
the commanded current level.
INTVCC
RSS

LT3932SS

CSS
3932 F10

Figure 10. SS Capacitor and Resistor Configuration

The SS pin is also used as a fault timer. After a fault is
detected, an internal 1.25μA current sink will begin todischarge the soft-start capacitor and lower the voltage
at the SS pin. When the voltage falls from 3.3V to 1.7V,
all switching will cease, but the SS pin will continue todischarge. Switching will not resume until SS reaches
200mV. At this point, the 20μA current will recharge thesoft-start capacitor, and the LT3932 will try to switch
again. If the fault persists when SS returns to 1.7V, theprocess will repeat as shown in Figure 11.
The charging rate of the soft-start capacitor is much fasterthan the discharging rate, so while the fault persists, theLT3932 will only attempt switching for a relatively shortpart of the cycle before being interrupted. Although theLT3932 can safely endure a short-circuit while continuously switching, this hiccup action saves power. The frequency of the hiccups is inversely proportional to CSS and
100nF yields about 8Hz.
The operating point of a voltage regulator supplying lightloads will frequently satisfy the criteria for an open-circuit,and the hiccup behavior would therefore be very disruptive. So when the LT3932 is configured as a voltage regulator, a resistor RSS should be connected between INTVCC
and SS as shown in Figure 10.
The current that pulls down the SS pin during a fault isso weak that if RSS is 1MΩ, the voltage at the SS pin will
never reach 1.7V. Therefore, the LT3932 will not stop
switching or start to hiccup. With this resistor, the LT3932
will continue switching and rely on overvoltage and overcurrent protection to guarantee safe operation in the eventof open-circuits and short-circuits.
If the resistor is changed to 2MΩ, then the SS pin may bedischarged to less than 1.7V, but not less than 200mV as
shown in Figure 12. The LT3932 will consequently cease
switching permanently until being reset by the EN/UVLO
pin or by powering off. Some applications may demand
this behavior so that short and open-circuits can be investigated manually before resuming normal operation.
This latch-off behavior is the third of three ways that theLT3932 can be programmed to respond to faults—theother two being continuous operation and the default hiccup behavior.

FAULT DETECTEDFAULT DETECTEDCONTINUOUS
RSS = 1MEG

SS
1V/DIVSS
1V/DIV

FAULT CLEARED
10ms/DIV

3932 F11

Figure 11. Hiccup Response to Fault

20

LATCH–OFF
RSS = 2MEG

10ms/DIV

3932 F12

Figure 12. Latch-Off Response to a Fault

Rev B

For more information www.analog.com

LT3932/LT3932-1
APPLICATIONS INFORMATION
Dimming with External Drivers
Continuous operation in response to a fault also enables
the LT3932 to operate with external switches that shuntsome or all of the LEDs in the string. The LT3965 8-switch
Matrix LED Dimmer, for example, is designed to shunta changing combination of up to eight LEDs in a single
string with independent PWM dimming signals. See
Typical Applications for more details.
Programming the EN/UVLO Threshold
An external voltage source can be used to set the voltage
at the EN/UVLO pin to enable or disable the LT3932. The
LT3932 will stop switching, disable the PWMTG driver,and reset the SS pin when the voltage at EN/UVLO drops
below 1.15V, but internal circuitry will continue drawing
current. Full shutdown is guaranteed when EN/UVLO isbelow 300mV, and in full shutdown the LT3932 will draw
less than 2μA. For applications in which the level of thesource driving EN/UVLO changes slowly, 20mV of hysteresis has been added to the 1.15V enable threshold.
Alternatively, a resistor network can be placed between
VIN and EN/UVLO as shown in Figure 13. In this case,
EN/UVLO automatically falls below 1.15V and disables
VIN
REN2

LT3932
EN/UVLO

REN13932 F13

Figure 13. EN/UVLO Resistor Configuration

switching when VIN falls below a certain level, called theUndervoltage Lockout (UVLO) threshold, which is definedby resistors REN1 and REN2. Additionally, a 4μA current
is designed to flow into EN/UVLO when the pin voltage
is below the threshold. This current provides additional
hysteresis. To define the hysteresis (VHYST) and the UVLO
threshold (VUVLO) select REN1 and REN2 according to thefollowing equations:
REN2 =

VHYST VUVLO–
4µA 480µA

REN1 =

1.15 • REN2VUVLO – 1.15

For example, to program a 10V threshold with 1V ofhysteresis, use 226k and 29.4k for REN2 and REN1,
respectively.
Planning for Thermal Shutdown
The LT3932 automatically stops switching when theinternal temperature is too high. The temperature limit isguaranteed to be higher than the operational temperatureof the part. During thermal shutdown, all switching is terminated, SS is forced low, and the LEDs are disconnectedusing the PWMTG driver.
The exposed pad on the bottom of the package must be
soldered to a ground plane. Vias placed directly under the
package are necessary to dissipate heat. Following theseguidelines, the official four-layer demo board DC2286A
reduces thermal resistance θJA to 25°C/W, but with a compromised board design θJA could be 40°C/W or higher.

Rev B

For more information www.analog.com

21

LT3932/LT3932-1
APPLICATIONS INFORMATION
Designing the Printed Circuit Board
Note that large switched currents flow through the local
input capacitors and the VIN and GND pins. The loops
traveled by these currents should be made as small as
possible by keeping the capacitors as close as possible
to these pins. These capacitors, as well as the inductor,
should be placed on the same side of the board as theLT3932 and connected on the same layer. Other large,
bulk input capacitors can be safely placed farther fromthe chip and on the other side of the board.
Create a Kelvin ground network by keeping the groundconnection for all of the other components separate.
It should only join the ground for the input and output
capacitors and the return path for the LED current at the
exposed pad.

22

There are a few other aspects of the board design that
improve performance. An unbroken ground plane on
the second layer dissipates heat, but also reduces noise.
Likewise minimizing the area of the SW and BST nodes
reduces noise. The traces for FB and VC should be kept
short to lessen the susceptibility to noise of these highimpedance nodes. Matched kelvin connections from theexternal current sense resistor RS to the ISP and ISN
pins are essential for current regulation accuracy. The
2.2μF INTVCC and VREF capacitors as well as the 22nF
BST capacitor should be placed as closely as possible totheir respective pins. A capacitor for the CTRL pin and,
when the internal dimming feature is used, the PWM pin,can compensate for compromised layouts. Finally, a diodewith anode connected to ground and cathode to the drainof the PWMTG MOSFET can protect that device from overvoltage caused by excessive inductance in the LED string.
Please refer to the demo board layout of the LT3932 foran example of how to implement these recommendations.

Rev B

For more information www.analog.com

LT3932/LT3932-1
TYPICAL APPLICATIONS
2A LED Driver with Duty Cycle LED Current
D1
INTVCC
VIN
36V

VIN
ENABLE
CIN1
10µF

EN/UVLO

CREF
2.2µF

RFAULT
100k
FAULT

CBST
22nF

L1
150µH

SW

CIN2
2×1µF
3.3V
0V
3.3V
0V

CVCC
2.2µF

BST

VOUT
CTRL

LT3932

FB

PWM
VREF

GND

RFB2
287k
RFB1
10k

COUT
2×10µF

L1: WURTH 7447709151
M1: VISHAY Si4447ADY
RS: OHMITE LVK12R050D
COUT1: MURATA GRM32ER71H106K
D1: NEXPERIA BAT46WJ
2A MAX

ISP
RS
50mΩ

INTVCC
ISN
FAULT

PWMTG

SYNC/SPRD
SS
CSS
100nF

ISMON
RT RP

RT
523k
200kHz

M1
ISMON

LED1

VC
CC
10nF

LED8

3932 TA02

Digital CTRL 50%,
Digital PWM 100%

Digital CTRL 25%,
Digital PWM 100%
CTRL
5V/DIV

CTRL
5V/DIV

PWM
2V/DIV

PWM
2V/DIVLED CURRENT
1A/DIVLED CURRENT
1A/DIV
500ns/DIV

3932 TA02a

500ns/DIV

Digital CTRL 25%,
Digital PWM 50%

Digital CTRL 25%,
Digital PWM 25%
CTRL
5V/DIV

CTRL
5V/DIV

PWM
5V/DIV

PWM
5V/DIVLED CURRENT
500mA/DIVLED CURRENT
500mA/DIV
5ms/DIV

3932 TA02b

3932 G33

5ms/DIV

3932 TA02d

Rev B

For more information www.analog.com

23

LT3932/LT3932-1
TYPICAL APPLICATIONS
24V Voltage Regulator with Spread Spectrum
D1
INTVCC
VIN
29V TO 36V

CIN1
10µF

CIN2
2×1µF

VIN

REN2
576k

BST
SW

EN/UVLO

REN1
23.7k

VOUT
LT3932FBISP

SYNC/SPRD

RSS
1MEGΩ

RFAULT
100k

CSS
10nF

PWMTG NOT USED

ISMON
RT

RP

VC
RC
20k
CC
10nF

RT
45.3k
2MHz

L1: COILCRAFT XAL5050-153
RS: OHMITE LVK12R050D
COUT: GRM32ER71H106K
D1: NEXPERIA BAT46WJ

3932 TA03

Efficiency

95

2.0

94

1.5

93

1.0

500
1000
1500
OUTPUT CURRENT (mA)VOUT
1V/DIV

2.5
ON–CHIP LOSS (W)EFFICIENCY (%)

Load Step Response (100mA to 1A)
3.0

EFFICIENCY (29VIN)
LOSS (29VIN)
EFFICIENCY (36VIN)LOSS (36VIN)

0

COUT
2 × 10µF

VOUT
24V, 2A MAX

FAULT
SS

L1
15µH

RS
50mΩ

ISN

INTVCC

CVCC
2.2µF

92

RFB2
10k

GND

CTRL
PWM

96

RFB1
226k

VREF

CREF
2.2µF

97

CBST
22nF

ILOAD
500mA/DIV
100µs/DIV

3932 TA03b

0.5
2000
3932 TA03a

24

Rev B

For more information www.analog.com

LT3932/LT3932-1
TYPICAL APPLICATIONS

D1
INTVCC

VIN
8V TO 36V

FB1
VIN
CIN1
2x100nF
50V
0402

CIN2
4.7µF
50V
1206

CIN3
33µF
50V
ELYT.

CIN4
1µF
50V
0603

CIN5
2x470nF
50V
0402

CREF
2.2µF

BST

CBST
22nF

REN2
232k
REN1
39.2k

L1
2.2µH

SW

EN/UVLO

VOUT
LT3932

VREF

RFB2
69.8k

FB

CTRL
PWM

RFB1
10k

GND

COUT
4.7µF
16V
0805

1A MAX

ISP
RS
100mΩ

ISN
RS: SUSUMU KRL1220D-M-R100-F
D1: NXP PMEG4010CEJ
FB1,2: WURTH 742792040
L1: WURTH 74438323022
M1: VISHAY Si2399DS
D1: NEXPERIA BAT46WJ

INTVCC
CVCC
10µF

PWMTG

FB2
SS

RT

RP

VC
RC
24.9k
CC
150pF

RT
45.3k
2MHz

CSS
1nF

ISMON, FAULT NOT USEDM1

SYNC/SPRD

CB2
100nF
16V
0402

LED1
D1

LED2
3932 TA07CISPR25 Peak Radiated Emissions Test
80

70

70

60

60
AMPLITUDE (dBµV/m)

AMPLITUDE (dBµV)

CISPR25 Peak Conducted Emissions Test
80

50
40
30
20
10
0
–10
–20
0.1

10
FREQUENCY (MHz)DC2286A DEMO BOARD
14V INPUT TO 6V OUTPUT AT 1A

50
40
30
20
10
0

CLASS 5 PEAK LIMITMEASURED EMISSIONSAMBIENT NOISE
1

CLASS 5 PEAK LIMITMEASURED EMISSIONSAMBIENT NOISE

–10
100

–20

200

0

60

50
40
30
20
10

DC2286A DEMO BOARD
14V INPUT TO 6V OUTPUT AT 1A

1000

3932 TA07b

20
10
0

100

900

30

–10
10
FREQUENCY (MHz)

800

40

–10
1

700

50

0

–20
0.1

400
500
600
FREQUENCY (MHz)

CLASS 5 AVERAGE LIMITMEASURED EMISSIONSAMBIENT NOISE70
AMPLITUDE (dBµV/m)

AMPLITUDE (dBµV)

60

300

CISPR25 Average Radiated Emissions Test
80

CLASS 5 AVERAGE LIMITMEASURED EMISSIONSAMBIENT NOISE

70

200

DC2286A DEMO BOARD
14V INPUT TO 6V OUTPUT AT 1A

3932 TA07a

CISPR25 Average Conducted Emissions Test
80

100

200

3932 TA07c

–20

0

100

200

300

400
500
600
FREQUENCY (MHz)DC2286A DEMO BOARD
14V INPUT TO 6V OUTPUT AT 1A

700

800

900

1000

3932 TA07d

Rev B

For more information www.analog.com

25

LT3932/LT3932-1
TYPICAL APPLICATIONS
2A LED Driver with Internal PWM Dimming
D1
INTVCC
VIN
12V TO 24V

VIN

BST

REN2
274k
CIN2
2×1µF

REN1
29.4k

RFB2
110k

LT3932

COUT
100µF

FB

CREF
2.2µF

RFB1
10k

CTRL
RREF2
100k

PWM

ISP
RS
50mΩ

ISN

RFAULT
100k
FAULT

2A MAXGND

INTVCC
CVCC
2.2µF

L1: WURTH 74404064082
M1: INFINEON IRF7204
RS: OHMITE LVK12R050D
COUT: AVX TPME107M020R0035
D1: NEXPERIA BAT46WJ

VOUT

VREF
RREF1
100k

L1
8.2µH

SW

EN/UVLO
CIN1
10µF

CBST
22nF

PWMTG
FAULT

ISMON

M1
ISMON

LED1

SYNC/SPRD
SS

CSS
100nF

RT RP
RT
45.3k
2MHz

VC
RP
28.7k
7.8kHz

LED2
RC
162k

LED3

CC
10nF
3932 TA06

Internal PWM DimmingSW
20V/DIVSW
20V/DIV

PWMTG
10V/DIV

PWMTG
10V/DIVIL
1A/DIVIL
1A/DIVILED
1A/DIVILED
1A/DIVPWM = 1.078V

26

Internal PWM Dimming

2µs/DIV

3932 TA06a

PWM = 1.132V

2µs/DIV

3932 TA06b

Rev B

For more information www.analog.com

LT3932/LT3932-1
TYPICAL APPLICATIONS
Multiple String Drivers from Single Boosted 36V Input
VBUCK
36V, 5A MAX

L0
4.2µH

D0

M0

VIN

GATE

SHDN/UVLO

SENSE
R0
4mΩ

SYNC

RSHDN112.1k

LT3757
GND

RFB1
348k
COUT +
35µF
50V

VIN
6V MIN FOR OPERATION
10V MIN FOR FULL CURRENT

CIN
10µF

RSHDN2
48.7k

RT
FBX

COUT
5µF

RFB2
16.2k

L0: WÜRTH 7443630420
M0: INFINEON BSZ040N04LS
R0: VISHAY WSLP25124L000F
D0: ONSEMI MBR1240MFS

INTVCC

SS

VC

RC
10k
CC
10nF

CVCC
4.7µF

CSS
100nF

RT
30.9k
400MHz+2 LT3932 (1A EACH)
D2

D1
INTVCCINTVCC
CIN1
10µF

CIN2
2×1µF

VIN

BST

EN/UVLO

VOUT

SW
ENABLE1
3.3V
0V
CREF
2.2µF

PWM

RCTRL249.9k
RCTRL1
30.1k
3.3V
0V

LT3932

VREF
CTRL

FB
GND

CSS
100nF

CIN2
2×1µF

CIN1
10µF

RFB1
110k
RFB2
10k

VIN

BST

EN/UVLO

VOUT

SW
ENABLE2
3.3V
0V

COUT
4.7µF

LT3932PWM

1A MAX

GND

CTRL

PWMTG
ISMON

RT

RP

VC

RT
45.3k
2MHz

L1: WURTH 74437336100
M1: INFINEON IRF7204
RS1: OHMITE LVK12R050D
COUT: MURATA GRM32ER714475K
D1: NEXPERIA BAT46WJ

RFB1
287k
RFB2
10k

L2
15µH

COUT
4.7µF
1A MAX

M1

RS2
100mΩ

SYNC/SPRD

RFAULT
100k

CSS
100nF

ISN

INTVCC

PWMTG
RT

M2

ISMON

FAULT
SS

CVCC
2.2µF
CC
10nF

CBST
22nF

ISP
3.3V
0V

ISN

FAULT

FB

VREF

CREF
2.2µF
RS1
50mΩ

INTVCC

SS

CVCC
2.2µF

L1
10µH

ISP
SYNC/SPRD

RFAULT
100k

CBST
22nF

RP

VC

RT
45.3k
2MHz

L2: COILCRAFT LPS8045B-153
M2: VISHAY Si2319CDS
RS2: OHMITE LVK12R100D
COUT: MURATA GRM32ER71H475K
D2: NEXPERIA BAT46WJ

8×
LED

CC
10nF

3932 TA05

Rev B

For more information www.analog.com

27

LT3932/LT3932-1
PACKAGE DESCRIPTIONUFD Package
28-Lead Plastic QFN (4mm × 5mm)

(Reference LTC DWG # 05-08-1712 Rev C)

0.70 ±0.05

4.50 ±0.05
3.10 ±0.05
2.50 REF

2.65 ±0.05
3.65 ±0.05

PACKAGE OUTLINE

0.25 ±0.05
0.50 BSC
3.50 REF
4.10 ±0.05
5.50 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONSAPPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ±0.10(2 SIDES)

R = 0.05
TYP

0.75 ±0.05

PIN 1 NOTCH
R = 0.20 OR 0.35
× 45° CHAMFER

2.50 REF
R = 0.115
TYP
27

28
0.40 ±0.10

PIN 1
TOP MARK(NOTE 6)1
2

5.00 ±0.10(2 SIDES)

3.50 REF
3.65 ±0.10
2.65 ±0.10(UFD28) QFN 0816 REV C

0.200 REF
0.00 – 0.05

0.25 ±0.05
0.50 BSC
BOTTOM VIEW—EXPOSED PAD

NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGHD-3).
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATIONON THE TOP AND BOTTOM OF PACKAGE

28

Rev B

For more information www.analog.com

LT3932/LT3932-1
REVISION HISTORY
REV

DATE

DESCRIPTION

A

02/18

Added LT3932-1 to data sheet.

1

Added 10000:1 PWM dimming ratio for LT3932-1 with supporting text in Features and Description.

1

Added machine vision systems to Applications.

1, 22, 24, 25, 28

On Figure, added Schottky Diode from INTVCC to BST pin, changed boost capacitor from 100nF to 22nF.

1, 12, 22, 23, 24,
25, 26, 28

Changed θJA from 43°C/W to 25°C/W (based on demo board measurement).

2

Sense voltage VCTRL changed from 2V to 1.5V. ISN pin current VISN value changed from 24V to 23.9V.

3

LED Current and LED Voltage Limit Graphs y-axis corrected to mV units.

7

DA Limit graph retitled to “DA Current Limit”, input step changed from 20V upper limit to 25V on Input Voltage
Transient Response graph.

9

Added additional BST pin description text; corrected BST capacitor value from 100nF to 22nF.

11

DA Current Limit added to Block Diagram.

12

Text added to describe DA Current Limit.

15

Added LT3932-1 text regarding four-cycle limit and machine vision usage.

18

Added text regarding θJA equals 25°C/W using DC2286 demo board, corrected boost capacitor value.

21

Corrected Typical Application figure, reduced VOUT from 30V to 24V, changed digital CTRL 50% graph y-axis
from 5A/DIV to 5V/DIV.

22

Added Diode D1: Nexperia BAT46WJ.
07/18

1

Relabeled Soft-Start pin from S to SS.

Add new Efficiency graph.
B

PAGE NUMBER

Three revised UVLO graphs in Typical Performance Characteristics
EN/UVLO description; Changed text from “A resistor network between this pin and GND” to “. . . this pin and VIN.”
VREF description; Changed buffered reference drive current from 2mA to 1mA
Corrected RSS from 1mΩ to 1MΩ
Changed Inductor L1 value from 7438323022 to 74438323022
Increased Inductor value from 8.2µH to 10µH
Changed Inductor; New Product Number; Changed L1 From 7440463082 to 74437336100

23
22, 24, 25, 26, 28
5
10
10
24
25
27
27

Rev B

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license For
is granted
implication orotherwise under any patent or patent rights of Analog Devices.
more byinformationwww.analog.com

29

LT3932/LT3932-1
TYPICAL APPLICATION
700mA Matrix LED Driver with Individual Dimming for 6 LEDs
D1
INTVCC
VIN
32V

VIN

BST

REN2
249k
CIN1
10µF
50V

CIN2
2x1µF
50V
0402

VOUT

D7
RFB2
267k

LT3932
VREF

RFB1
10k

RREF2
110k

GND
CTRL

REN4
249k

RDD
100k

700mA

VIN

EN/UVLO
REN3
10.7k

D8
D7

ISP

RREF1
105k

VDD

COUT
22nF

FB

CREF
2.2µF

L1: WURTH 74437349330
D1-7: NXP PMEG4010CEJ
RS: OHMITE LVK12R100DER
D1: NEXPERIA BAT46WJ

L1
33µH

SW

EN/UVLO
REN1
10.2k

CBST
22nF

S8

RS
100mΩ

S7

LT3965

ISN
D6
D6

PWM

START

SYNC/SPRD

SS
RPWM
10k

RSS
1M

CSS
10nF

VDD
RSDA
10k

S6

INTVCC
CVCC
2.2µF

LED6

RT

RP

RT
287k
350kHz

D2

VC

D2

LED2

CC
330pF

S2
D1
D1

LED1
S1

RSCL
10k

RALERT
10k

SDA
SCL

CVDD
2.2µF

ALERT
PWMCLK
350kHzADDR1-4 GND LEDREF

3.3V
0V

PWMTG, FAULT, AND ISMON NOT USED3932 TA04

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30

Rev B
D16990-0-7/18(B)www.analog.com
For more information www.analog.com

 ANALOG DEVICES, INC. 2018