ELM901FxA 1A 2x Charge Pump LED Driver

http://www.elm-tech.com■General description

ELM901FxA is a high current LED driver with internal automatic mode switch pump circuit of pass-throughmode (1x mode) and boost charge mode (2x mode) and constant current drive circuit; maximum output currentof ELM901 series can reach 1A. ELM901 series is ideally suited for high luminosity white LED electricalapplications which are powered by 1-cell lithium-ion/polymer battery. The required external parts of ELM901
series can be limited to the minimum of 3 capacitors and 3 programming resistors. With 4mm x 4mm & 3mm x
3mm QFN package, ELM901 series is possible to be assembled within limited space.
The sink current, which can be switched to 3 different kinds by enable signal during operation,of LED pin isset by external programming resistors. For LED protection, it is possible to set high current lighting timer withexternal resistor; the light will be turned off forcibly by timer (3 options among 0.2 sec. to 1 sec.).
Built-in soft-start circuitry makes ELM901 series be able to limit excessive power during start-up and switch
of 1x & 2x mode.

■Features■Application• Low voltage operation: 2.6V-4.4V• Camera light supply• High luminosity LED flashlight• Low power operation: 300μA(1x), 9mA(2x)• Low standby current: Max.1μA• Large output current: Max.1A• LED protection: high current lightening timer• Internal LED constant current circuit: external resistance program• Soft-start: LED current start and switch of 1x & 2x mode
• Package: QFN16-4x4,
QFN16-3x3(under development)• Thermal shutdown function included■Maximum absolute ratings
Parameter
VIN voltage
VO voltage
EN1,EN2 voltage
VO current, LED current
Operating temperature
Storage temperature

SymbolVin
Vo
Ven
Io, Iled
Top
Tstg

Limit
GND-0.3 to 6
GND-0.3 to 6
GND-0.3 to Vin+0.3
1500 *-40 to +85-40 to +125

Unit
V
V
V
mA
°C
°C

* Based on long-term current denslty limitations. Assumes an operating duty cycle of ≤ 10% under absolute maximum conditions fordurations less than 10 seconds. Max current for continuous operation is 600mA.

■Selection Guide
ELM901FxA-S
Symbola

Packageb

Package typecd

Product version
Taping direction

F: QFN
A: QFN16-4x4
B: QFN16-3x3(under development)A
S: Refer to PKG file

ELM901 F x A - S
↑↑↑ ↑
abc d

Rev.1.0
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ELM901FxA 1A 2x Charge Pump LED Driver
http://www.elm-tech.com■Pin Configuration
QFN16-4x4(TOP VIEW)
12

11

10

QFN16-4x4(BOTTOM VIEW)
9

9

10

11

12

13

8

8

13

14

7

7

14

15

6

6

15

16

5

5

16

1

2

3

4

4

QFN16-3x3(TOP VIEW)
12

11

10

3

2

1

QFN16-3x3(BOTTOM VIEW)
9

9

10

11

12

13

8

8

13

14

7

7

14

15

6

6

15

16

5

5

16

1

2

3

4

4

3

2

Pin no.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

Pin name
ISET2
ISET1
EN2
EN1
AGND
FS
VIN
PGND1
CM
PVIN
CP
NC
VO
NC
PGND2
LED

1

■Pin description
ISET2 : LED current setting 2
The pin that is for the connection of LED current setting resistor(Rset2) between ISET2-GND. The output
becomes 1.22V constantly when EN2 is high. The constant current of LED pin will be 3250x of the one
flows to ISET2.
(e.g.) when Rset2=6.8kΩ, Iled=1.22/6.8k×3250=583mA.
ISET1 : LED current setting 1
The pin that is for the connection of LED current setting resistor(Rset1) between ISET1-GND. The output
becomes 1.22V constantly when EN1 is high. The constant current of LED pin will be 3250x of the one
flows to ISET1.
(e.g.) when Rset1=20kΩ, Iled=1.22/20k×3250=198.3mA.
EN2 : on/off control 2
LED output current on/off control pin of set current of ISET2. This pin is pulled down to ground inside
the IC and the control logic is high active. The set current of ISET2 sinks from LED pin when this pin isconnected to VIN.

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ELM901FxA 1A 2x Charge Pump LED Driver
http://www.elm-tech.com
EN1 : on/off control 1
LED output current on/off control pin of set current of ISET1. This pin is pulled down to ground inside
the IC and the control logic is high active. The set current of ISET1 sinks from LED pin when this pin isconnected to VIN.
AGND : internal analog circuit ground
This pin should be connected to GND of internal analog circuit and is connected in short circuit with internal
circuit on back pad. The connection to PGND1 & PGND2 is required and should be designed according to
the external wiring.
FS : fail safe setting
When EN1=EN2=1 continues for a period of time, fail safe function will turn down LED current forcibly.
This function aims for thermal protection of LED, and it is possible to be turned off. There are 3 timer
options according to the resistor connected between FS and GND since EN1=EN2=1 until LED current isoff: (1)1s when the resistor is short, (2)0.2s when the resistor is 20kΩ, and (3)0.5s when the resistor is 51kΩ.
This fail safe function becomes ineffective when it is short between FS and VIN or FS is open.
VIN : internal circuit power
This pin should be connected to the power pin of internal circuit. The connection to PVIN is required andshould be designed according to the external wiring; GND-connected ceramic capacitor( above 2.2μF) isalso necessary.
PGND1 : charge pump circuit ground
This pin should be connected to GND of charge pump circuit. The connection to AGND & PGND2 isrequired and should be designed according to the external wiring.
CM : step-up capacitor connection( low potential)
This pin should be connected to the low potential of step-up capacitor. The wiring of step-up capacitor
should be connected between CM and CP as closely as possible; ELM recommends using 2.2μF capacitor.
PVIN : charge pump power
This pin is power supply of charge pump circuit. This pin should be connected to VIN according to theexternal wiring.
CP : step-up capacitor connection( high potential)
This pin should be connected to the high potential of step-up capacitor. The wiring of step-up capacitor
should be connected between CM and CP as close as possible; ELM recommends using 2.2μF capacitor.
VO : step-up output
The output voltage is almost the same as VIN under 1x mode, while it becomes 5.5V under step-up mode.
This pin should be connected to LED anode.
PGND2 : LED current drive circuit ground
This pin should be connected to the GND of LED current drive circuit. The connection to AGND & PGND1
is required and should be designed according to the external wiring.
LED : constant current sink
To sink the output current which is set by ISET1 & ISET2. This pin should be connected to LED cathode.

Rev.1.0
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ELM901FxA 1A 2x Charge Pump LED Driver
http://www.elm-tech.com■Standard circuit
C2
12

NC 11 CP 10 PVIN 9 CM

13

●

8

Charge pump

VO

C1

14

7

NC

LED

PGND1

15

PGND2

●

C3

6

FS

CC Control

16

●

VIN

900kHz OSC
Timer

Rfs

5

LED

AGND
1 ISET2 2 ISET1 3

Rset1

Rset2

PVIN

CP

EN2 4

EN1

●

■Block diagram

VIN

x1/x2 charge pump▲

Thermalprotection

CM

▲ ▲▲▲

▲

▲

▲

VO
▲

Step-upcircuitVref

900kHzoscillator

EN2

PGND1

x1/x2 switch

Control logic

Short protection▲▲

Drop out detection

Current sense control

ISET1

LED

▲

▲

EN1

Vref(soft)

Fail safe circuit

▲

FS

AGND

ISET2

PGND2

Rev.1.0
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ELM901FxA 1A 2x Charge Pump LED Driver
http://www.elm-tech.com■Operation

ELM901 is designed to drive high luminosity LED which is powered by 1 lithium-ion/polymer battery withconstant current. When the battery voltage is much higher than LED forward voltage, LED is lit by connecting
directly to the battery; output voltage is stepped up to 5.5V by internal charge pump circuit to light LED whenvoltage drops. LED current is driven by the constant current circuit which is set by external programming resistors. With 2 types of LED current programming resistors, 3 current-driving options can be designed by different
combinations of enable circuit. ELM901A is capable of supplying output current up to 1A and thus able to provide high luminosity. To avoid LED burnout caused by longtime lighting by large current, the internal lighting
timer of ELM901A can shut down current forcibly. The timer only operates when maximum setting current ison and can be set to 3 options-0.2s, 0.5s, 1s by external resistors connected to FS. This timer can be turned off
when it is short between FS and VIN or FS is open.
Operation right after power is supplied
ELM901 becomes standby operation when EN1=EN2=0 or open(standby); unde this operation, highresistance PMOS switch between VIN and VO becomes ON. PMOS switch (=switch 4) between CP and
VO and NMOS switch (=switch 1) between CM and PGND1 also become on. Hence, output capacitor Co
and flying capacitor C1 are gradually charged through high resistance PMOS switch; it takes 5ms to fullcharge after the power is on. Rush current may happen when operation starts within 5ms after power is on.
Standby mode
In this mode, output capacitor Co and flying capacitor become fully charged, and through individual highresistance PMOS switch, VIN is turned to be output mode. With maintenance of fully-charged mode during
standby situation, it is possible to avoid rush current when operation begins and lighten LED rapidly.
Start-up mode
During start-up, ELM901 detects VO short first; the low resistance switch between VIN-VO becomes on
and operates in 1x mode if short is not detected. When short is detected, Vo maintains the same condition as in standby mode, the output of LED also remains off while other internal circuits are operated normally. 1x mode is operated right after short is solved. It takes 30ms(typ.) from start-up to 1x mode output.
Vo=Vin under normal operation, and inrush current does not occur due to the charge of capacitor. Whenabnormality (Vo>0.7V) such as short between VO and GND which is resulted from resistance of 10~1KΩ,
inrush current occurs due to the charge of capacitor. LED current becomes ON after 130μs(typ.) after starpup; it takes less than 100us since LED current becomes ON until the set current flows.
1x modeWhen dropout of LED pin is detected under 1x mode, the operation switches to 2x mode automatically.
When LED current works under “low” current mode, the operation remains 1x mode for around 150ms
even if the dropout of LED pin is detected; if dropout is dissolved during this period of time, timer is resetand 1x mode continues. When the operation is by “high” or “low+high” current, it becomes 2x mode after
2ms; if dropout is dissolved during this period of time, timer is reset and 1x mode continues. Dropout detection voltage is in proportion to Iled when it is above 240mA(typ.) and the voltage is regulated to 100mV
when Iled is small.

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ELM901FxA 1A 2x Charge Pump LED Driver
http://www.elm-tech.com
Soft step-up
The operation becomes soft step-up by charge pump operation right after 2x mode starts. Rush current isdecreased by soft step-up which increases Vo straight. The current is controlled when Iled becomes 1/2 ofthe setting during soft step-up. Iled is limited under 350mA(typ.) forcibly to avoid abrupt change of Iled
within 10us after step-up operation starts. Iled control current returns to the setting after step-up is finished.
2x modeAfter switching to normal 2x mode, operation remains this mode until standby mode(EN1=EN2=GND)
starts. To work under 1x mode again, it is necessary to restart after switching to standby mode.

■Protection function
Thermal protection
When junction temperature becomes over 150°C, Vo output is turned to be OFF (only high resistance
PMOS switch is ON)thermal shutdown circuit and LED output is shut down by thermal shutdown circuit.
To shut down thermal protection, it is necessary to restart operation after returning to standby mode.
ISET1/ISET2 short protection
When EN1=0→1 during start-up, if Rset which is connected to ISET1 is under 3.9kΩ(setting current ofIled is above 1A),LED current which is the same with[low] current is shut down. If ISET2 is under normal
operation under this situation, LED current which is the same with[high] current is flowed. When it is short
between ISET1 and GND under the operation that EN1=1, LED current limit is detected by 1.5A and shut
down without flowing to EN logic.
When EN2=0→1 during start-up, if Rset which is connected to ISET2 is under 3.9kΩ( setting current ofIled is above 1A), LED current which is the same with[high] current is shut down. If ISET1 is under normal operation under this situation, LED current which is the same with[low] current is flowed. When it isshort between ISET2 and GND under the operation that EN2=1, LED current limit is detected by 1.5A andshut down without flowing to EN logic.
LED current becomes 0 when [low]+[high]current reaches 1.5A under EN1=EN2=1 under the above-mentioned 2 situations.
VO short protection
When VO lowers to around 0.7V during operation, device shuts down the outputs of both Vo and LED; Vin
and Vo become connected by high resistance PMOS switch(standby output) under this situation. After VO
short is dissolved and Vo rises above 0.7V, outputs of Vo and LED restart. When VO short is detected under 2x mode, the operation switches to standby mode.
Fail safe function
Fail safe function refers to the function that the output of LED is turned to be OFF automatically when“low+high” current(EN1=EN2=1) continues for certain period of time. To dissolve the function that LED
output is turned to be OFF forcibly, it is necessary to switch EN1=EN2=1 to other modes. 3 options areavailable for FS time; FS time is set by external resistors (Rfs). This function can be turned off by setting
short between FS and VIN pins or FS to be open.

Rev.1.0
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ELM901FxA 1A 2x Charge Pump LED Driver
http://www.elm-tech.com■Electrical characteristics

When conditions are not mentioned specifically, Vin=3.6V, Cin=C1=2.2μF, Co=4.7μF, Ta=25°C
Parameter
SymbolCondition
Min.
Typ. Max.
Unit
Input voltage range
Vin
2.6
4.4
V
current consumption underIqs1 1x mode, Iled=0mA
300
550
μA
still condition 1
current consumption underIqs2 2x mode, Iled=0mA
916mA
still condition 2Standby current
Isd
EN1=EN2=0V
0.1
1.0
μA
LED current
LED current ratio1
typ.×
typ.×
Iled1 Vin=3.8V, Iled=200mA, Vf=3.3V
3250
mA/mA
(Iled/Iset1/2)
0.96
1.04
Vin=3.3 to 4.4V,
LED current ratio2
typ.×
typ.×
Iled2
3250
mA/mA
(Iled/Iset1/2)
Iled=200 to 800mA
0.90
1.10
Vled1 Mode switch threshold voltage,
Iled dropout voltage1
125
225
mV
(Min.) Iled=300mA
Vled2 Mode switch threshold voltage,
Iled dropout voltage2
80
100
120
mV
(Min.) Iled=150mA
Mode switch delay time1
Td1 EN1=High, EN2=Low
100
150
200
ms
Mode switch delay time2
Td2 EN1=Low or High, EN2=High12
3
ms
since EN is ON until LED current
LED current on timeLED(on)
50
130
250
μs
startsIled Vin=3.3V, EN1=EN2=High, set
Current capability
900
mA(Max.) Iled=1A, VF=4.6V
LED current stablize time1
TIled1 Iled=0mA→200mA
40μs
LED current stablize time2
TIled2 Iled=200mA→700mA
60μs
LED current during soft
Iled
set Iled=700mA
250
350
450
mA
step-up(soft)
Charge pump
Soft step-up
Tsoft Iled=700mA, Vo=3.7V→5.2V
75
150
300
μs
1x mode output voltage
Vo(x1) Iled=0mA
Vin
V
typ.×
typ.×
2x mode output voltage
Vo(x2) Iled=0mA
5.5
V
0.95
1.05
1x mode output impedanceRo(x1) Vin=3.4V
0.25
0.37
Ω
(2Vin-Vo)/Io, Vin=3.2V,
2x mode output impedanceRo(x2)
1.70
2.55
Ω
Vo=5.1V
Oscillation frequency
Fosc
0.72
0.90
1.08
MHz
EN1, EN2
Output on control voltage
Vc(ON) Vin=2.9 to 4.4V, each pin
0.95
V
Vc(OFF) Vin=2.9 to 4.4V, each pin
0.45VOutput off control voltage
EN bias current
Ic(ON) Ven=3.6V, each pin
2050
μA
ISET1, ISET2
Reference voltage
Vref Iset=50μA, each pin
1.202 1.220 1.238
V
ISET set current
Iseteach pin
310
μA

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ELM901FxA 1A 2x Charge Pump LED Driver
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Parameter
Short protection circuit

SymbolConditionMin.

ISET1&2 turn Iled to be OFF
Iled
Iled limit when ISET is shortfor short protection, Vin=3.9V,(short)Vled=1.0V, 2x operation
Iled is OFF when short protection
VO short protection detection
Vo
0.45
voltage(short) is activatedVO short current
Ishort Vin=3.6V
Thermal protection circuit
Iled is OFF when thermal
Thermal protection circuit
OHP
protection circuit is activatedFail safe circuit
Tfs
Fail safe set range
0.2(range)Fail safe function is OFF when
Fail safe time1
Tfs1 *
0.80
FS-VIN is short or open.
Fail safe time2
Tfs2
0.16
Fail safe time3
Tfs3
0.40
Fail safe current
Ifs
10
FS threshold voltage1
Vfs1
0.120
FS threshold voltage2
Vfs2
0.405
FS threshold voltage3
Vfs3
1.080
Parameter
EN logic & LED current
EN logicStandby(output OFF)Low current
High current
Low+High current

Typ.

Max.

Unit

1.5
0.60

A
0.95

V

30

mA

150

°C

1.00
0.20
0.50
15
0.150
0.450
1.220

1.0

s

1.20
0.24
0.60
20
0.180
0.495
1.360

s
s
s
μA
V
V
V

Condition
EN1
0
1
0
1

EN2
0
0
1
1

* EN1 & EN2 will be in standby mode when being
pulled down to be open.

■Marking• QFN16-4x4 package : ELM901FAA

Mark
ELM901FAA
abc(000 to 999)

• QFN16-3x3 package : ELM901FBA

Content
Name

Mark
ELM901FBA
abc(000 to 999)

Assembly lot No.

Content
Name
Assembly lot No.

Rev.1.0
8 / 11

ELM901FxA 1A 2x Charge Pump LED Driver
http://www.elm-tech.com■Typical characteristics
EFFICIENCY-Vin
ILED=
200mA

400mA

600mA

80

Dropout Voltage (V)EFFICIENCY (%)

90
70
60
50

Dropout Voltage-Iled

0.5

LED = LUMILEDS LXHL-LW3C

100

800mA

40
30
20

0.4

0.3

0.2

0.1

10

0

2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4

Iled-Rset

Iled (mA)

900

900

800

800

700

700

600
500
400

200

100

100

0

0 20 40 60 80 100 120 140 160 180 200

Rset (k�)

100mA

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

2x Mode Output Resistance - Top

1x Mode Output Resistance - Top

Vin=3.2V, Vo=4.8V

2.5
Vin=3.3V

0.2

0.15

Vin=3.6V
Vin=3.9V

0.1

0.05
0
-40

200mA

Vled (V)2x Mode Output Resistance (�)1x Mode Output Resistance (�)

0.25

400mA

400

200
0

600mA

500

300

-20

0

20

40

Top (�)60

1000

Iled=800mA

600

300

800

Iled-Vled

1000

Iled (mA)

Iled (mA)

1000

600

400

200

Vin (V)

2

1.5

1

0.5

0
-40

80

-20

0

20

40

Top (�)60

80

Rev.1.0
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ELM901FxA 1A 2x Charge Pump LED Driver
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Isd-Vin

0.1

920
Top=85�

Frequency (kHz)Isd (�A)

0.08
0.06
0.04

Top=25�

0.02

Vref-Top

Iled/Iset Ratio-Top

3280

Iled/Iset Ratio

Vref (V)

1.21

3260
3240
3220

-20

0

20

40

Top (�)

60

3200
-40

80

EN Pin Input Current-Top

0.9

EN Thereshold Voltage (V)EN Pin Input Current (uA)

Top= -40�

3300

1.22

25

20

15

10
-40

860

Vin (V)

1.23

30

880

820
2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4

Vin (V)

1.24

Top=85�
Top=25�

900

840

Top=��40�

0
2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4

1.2
-40

Frequency - Vin

940

-20

0

20

40

Top (�)

60

0

20

40

Top (�)60

80

EN Threshold Voltage-Top

0.8

0.7

0.6

0.5
-40

80

-20

-20

0

20

40

Top (�)60

80

Rev.1.0
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ELM901FxA 1A 2x Charge Pump LED Driver
http://www.elm-tech.com
Iled Start Response

Iled/Iset Ratio-Iled3350

Vin=3.6V, Iled=0mA�200mA

300

200
Top=85�

Iled (mA)

3250

Top=25�0

V(EN1) : 0V � 3.6V

Top= -40�

3200

3150

100

0

200

400

Iled (mA)

600

800

0

40

Iled

0

Vo

Vo, V(EN2)(2V/Div)

240

Time (us)

320

400

Vin=3.6V, Iled=800mA

Iled (mA)

Iled (mA)

Vin=3.6V, Iled=200mA�800mA

400

160

Iled, Vo Ripple Voltage

1x to 2x Mode Switch Response
800

80

Iled A/C Coulpled

20
0
-20
-40

200

Vo A/C Coulpled

V(EN2) : 0V � 3.6V

100
0
-100

0

0.8

1.6

2.4

Time (ms)

3.2

4

0

2

4

6

Time (us)8

Vo (mV)

Iled/Iset Ratio

3300

-200
10

Rev.1.0
11 / 11