ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com■General description

ELM615DA is a high-efficiency, high-voltage, synchronous step-down DC-DC converter with integrated
high-side and low-side power MOSFETs. ELM615DA uses proprietary constant on-time (COT) control toprovide excellent line and load transient response. ELM615DA features slew rate control and spread spectrum
frequency modulation to minimize EMI/EMC emissions. With wide input range from 4V to 36V, the converter
can deliver output voltage ranging from 0.8V to VIN with up to 5A continuous output current. The converter
can be configured as single output or dual outputs with independent constant current (CC) regulation for each
output. In the event of output overload or short circuit, the converter will be into hiccup mode. Other protection
features include cycle-by-cycle current limit, input under and over voltage protection and thermal shutdown.
ELM615DA also provides programmable cable voltage drop compensation by selecting an appropriate external
resistor of the divider net work divider. Switching frequency is internally set to 180kHz. ELM615DA isavailable in SOP-8_EP package.
VIN

4V~36V

Cin1 Cin2
100uF 10uF

■Features

Cin3
0.1uF

VIN

BST

VCC

SW

Cvcc
1uF

Cbst
100nF
L 22uH

Vout~120mΩ
USB Cable 1

Co1 Co2 R1Cff
10uF 220uF 240k 1nF
MT3901 ■Application• Input voltage range: 4V to 36V
AGND• Output current
: 5A
PGND
• Overcurrent protection: Switch cycleEP• Built-in wiring resistance voltage drop compensation circuit• Short circuit protection: Hiccup mode
• Overheat protection: 155°C• Spread spectrum switching: 180kHz 6% FM spread• Integrated switch on resistor : 40mΩ high side/40mΩ low side
• Minimum on time
: 70nsec• Soft start: 3msec• Package: SOP-8 (Exposed pad on back side)

USB1

5V/2.4A• Dual-port car charger
R2
RS1• Automotive andSupplies
45.3k Industrial
25mΩ
IS2• Point of Load
FB

IS1

RS2
25mΩ
USB Cable 2

Vout~120mΩ

5V/2.4A
USB2■Standard circuit
E f f iciency

4V~36V

Cin1 Cin2
100uF 10uF

Cin3
0.1uF

Cvcc
1uF

VIN

BST

VCC

SW

ELM615DA
MT3901

AGND
PGND
EP

100%

Cbst
100nF
L 22uH

Vout

Co1
10uF

Co2 R1
220uF 240k

~120mΩ
USB Cable 1

Cff
1nF

USB1

98%

5V/2.4A

Efficiency(%)

VIN

FB
R2
45.3k

RS1
25mΩ

IS2
IS1

RS2
25mΩ
USB Cable 2

Vout~120mΩ

96%
94%
92%
90%

12Vin5Vo

88%

24Vin5Vo
12Vin9Vo

86%

5V/2.4A
USB2

84%

24Vin9Vo
0.01

0.1

Io(A)

1

10

Rev.1.0
1 / 13E f f iciency

ELM615DA
36V 5A synchronous Step-down converter with dual-channel current limit

https://www.elm-tech.com■Selection guide
ELM615DA-N
SymbolabcdPart No.
Package
Product version
Taping direction

ELM615
D: SOP-8 (With exposed back pad)A
N: Please refer to page 13

ELM615 D A - N
↑
↑ ↑ ↑
a
b c d

* Taping direction is one way.

■Maximum absolute ratings (1)Parameter
Supply voltage Vin to GND

Symbol
VIN

Limit
+39

Unit
V

PGND-GND Supply voltag
SW-GND Supply voltag
SW-GND Surge voltage (30ns)

VPGND
VSW

-0.3 to +0.3
-0.3 to VIN+0.3

V
V

VSW_S

-3 to VIN+3

V

BST-SW Supply voltage

VBST-0.3 to +6.0

V

All Other Pins to GND
Lead temperature

VALL
TL

-0.3 to +6.0
+260

V
°C

Junction temperature
Storage temperature range
Thermal resistance (3), (4)

TJ
TSTG
θJA

+150
-65 to +150
51

°C
°C

Thermal resistance (3), (4)Power dissipation (3), (4)

θJC
PD

13
2.1

°C/W
W

■Recommend operating conditions (2)Parameter
Input voltage
Output voltage
Operating temperature range

Symbol
VIN
VOUT
TOP

Limit
+4 to +36
0.8 to VIN-40 to +125

Unit
V
V
°C

Note:
(1) Stress exceeding those listed “Maximum absolute ratings” may damage the device.
(2) The device is not guaranteed to function outside of the recommended operating conditions.
(3) Measured on JESD51-7, 4-Layer PCB.
(4) The maximum allowable power dissipation is a function of the maximum junction temperature TJ_MAX, the junction
to ambient thermal resistance θJA, and the ambient temperature TA. The maximum allowable continuous power dissipation at any ambient temperature is calculated by PD_MAX= (TJ_MAX-TA)/θJA. Exceeding the maximum allowable
power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Internal
thermal shutdown circuitry protects the device from permanent damage.

Rev.1.0
2 / 13

ELM615DA
36V 5A synchronous Step-down converter with dual-channel current limit

https://www.elm-tech.com■Pin configuration
SOP-8(TOP VIEW)
FB

�

�

IS2

VCC

�

�

IS1

BST

�

�

GND

SW

�

�

VIN

PGND

Exposed pad on backside

Pin NoSymbolPin description

1

FB

Feedback input.
Connect FB to the center of the external resistor divider from the output to the AGND
to set the output voltage.

2

VCC

Internal 5V LDO output.
The driver and control circuits are powered from this voltage. Decouple with aminimum 1μF ceramic capacitor to PGND as close to the pin as possible.

3

BST

High-Side driver bootstrap supply.
Connect a 0.1μF capacitor between SW and BST for proper operation.

4

SW

Output pin of internal power switches.
Connect this pin to the inductor and bootstrap capacitor.

5

VIN

Supply voltage.
The VIN pin supplies power for internal MOSFET and regulator. ELM615DA operates
from a +4V to +36V input rail. Bypass VIN to PGND with a 10μF or greater low ESR
ceramic capacitor.

6

GND

System analog ground.

7

IS1

IS1: The Channel 1 output current sense input pin.
Connect a sense resistor from this pin to AGND. When the voltage on this pin
increases to 60mV, ELM615DA reduces output voltage and regulates IS1 at 60mV.

8

IS2

IS2: The Channel 2 output current sense input pin.
Connect a sense resistor from this pin to AGND. When the voltage on this pin
increases to 60mV, ELM615DA reduces output voltage and regulates IS2 at 60mV.

EP

PGND

Exposed Pad is connected to the low side MOSFET Power Ground. Connect EP to alarge-area

Rev.1.0
3 / 13

ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com■Block diagram

VIN

VCC

EN

VCCREG

Bootstrap
Regulator

ULVO/OVP/OTP

BST

Soft-strat
BG

PWM
Comparator

VREFSS

SpreadSpectrum

Error
Amplifier

VREF

OnTimeM1

PWM

HS
DriverControl
Logic

SW
VCC

M2

LS
Driver

Cable
Drop
compensation

FB
Error
Amplifier

IS1

Error
Amplifier

PGND

HiccupMode
Zero - Current
Comparator+

Valley - Current
Comparator+

Peak - Current
Comparator

60mV

+

LSREF

HSREF

AGND

IS2

Fig-1. ELM615DA car charger functional block diagram (IS1/IS2)

Rev.1.0
4 / 13

ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com■Electrical characteristics
Parameter
Operating input voltage
Input under voltage lockout
threshold rising
Input under voltage lockout
threshold hysteresis
Input over voltage lockout
threshold rising
Input over voltage lockout
threshold hysteresis
VCC regulator
Supply current (quiescent)High-side switch on resistanceLow-side switch on resistance

VIN = 12V, TA = +25°C, unless otherwise noted.

Symbol
VIN

Min.
4

Typ.
-

Max.
36

Unit
V

VUVLO

-

3.80

4.05

V

VUVHYS

-

430

-

mV

VOVLO

-

38.3

-

V

VOVHYS

-

1.8

-

V

4.8
-

5.1
100
40
40

5.4
-

V
μA
mΩ
mΩ

-20

-

+20

μA

784
-100
-

800
70
100
100
7.5
6.5
90
155
25
180
3

816
+100
-

mV
nA
ns
ns
%
A
A
mA
°C
°C
kHz
kHz

-

+0.6

-

V

-

60

-

mV

VCC
ICC

RON_HS
RON_LS

Test conditions

VFB=0.84V, IVCC=0 to 30mA
VFB=0.84V
VFB=0.84V, VIN=36V
Vsw=0V or 36V

Switch leakage

ISW_LEAK

Feedback regulation voltage
Feedback pin Input current
Minimum on time
Minimum off time
Maximum duty cycle
High-side switch peak current limit
Low-side switch valley current limit
Low-side switch zero current detection
Thermal shutdown
Thermal shutdown hysteresis
Switching frequency
Spread-spectrum modulation frequency

VFBREGIFB
VFB=0.8V
TON_MIN
TOFF_MINDMAX VIN=12V, VFB=0.7V
IPK
IVALLEY
IZX
TSD1
TSD2
FSW

VIN=12V, R1=240kΩ
IOUT=IOUT1+IOUT2=5A

Output voltage cable compensation
IS1 / IS2 reference voltage

VIS

Rev.1.0
5 / 13

ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com■Typical characteristics• Circuit of Fig-1, CIN=100μF, COUT=10μF+220μF, L=22μH, RIS1=RIS2=20mΩ, TA=+25°C
Standby Current vs Input Voltage

6

300

5

250

Standby Current(uA)

Voltage(V)CV/CC Curve

4
3
2

12Vin5V
o

1
0

0

1

2

3

200
150
100
50
0

4

12

Output Current(A)Steady State Test

VOUT
50mV/div
VIN
5V/divSW
5V/divIL
1A/div

VIN=12VSW
5V/div

IOUT=0A

4ms/div

SW
5V/divIL
5A/div

VIN=12V

VIN
10V/div

SW
10V/div

IOUT=5A

4us/div

36

Steady State Test

VOUT
200mV/div
VIN
10V/div

VOUT=5VSW
10V/div

IOUT=5A

4us/div

IL
5A/div

VIN=24V

VOUT=12V

IOUT=5AIL
5A/div

Steady State Test

VOUT
200mV/div

VOUT=9V

VIN=12VIL
5A/div

Steady State Test

VOUT
50mV/div
VIN
5V/div

28

Steady State Test

VOUT
50mV/div
VIN
5V/div

VOUT=5V

20
Input Voltage(V)4us/div

Short Protection

VIN=24V

VIN
10V/div

VOUT=9V

VOUT
2V/div

VIN=12V
VOUT=5V
IOUT=0A~ShortSW
5V/div

IOUT=5A

4us/div

IL
5A/div

4ms/div

Rev.1.0
6 / 13

ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com• Circuit of Fig-1, CIN=100μF, COUT=10μF+220μF, L=22μH, RIS1=RIS2=20mΩ, TA=+25°C
Vin Power on
VIN
5V/divVin Power off
VIN
5V/div

VIN=12V

VOUT
2V/div

VOUT=5V

VOUT
2V/div

VIN=12V

VIN
10V/div

VIN=12V

VOUT=5V

VOUT
2V/div

IOUT=Short~0A

SW
5V/divSW
5V/divIL
1A/divIL
1A/div

IOUT=0A

IOUT=0A
10ms/div

Vin Power onIL
5A/divVin Power off

VIN=12V
VOUT=5V

VIN
5V/div
VOUT
2V/div

VOUT=5VSW
5V/div

10ms/div

VIN
5V/div

Short Protection

VIN=12V

4ms/div

Load Transient

VOUT
500mV/div

VOUT=5V

VIN=12V
VOUT=5V

VOUT
2V/divSW
5V/div

IOUT=5AIL
5A/div

10ms/div

SW
5V/divIL
5A/div

CV mode to CC mode
VOUT
1V/div
VOUT=5V to 4V

IOUT1=0A
IOUT2=0.5A~2.5A

4ms/div

200us/div

CC mode to CV mode

VOUT
1V/div

VIN=12VIL
2A/div

IOUT=5A

Load Transient

VOUT
500mV/div
VIN=12V

VIN=12V
VOUT=5V

VOUT=4V to 5VIL
2A/divIL
2A/div

400us/div

IOUT1=2.5A
IL
2A/div
80us/div

IOUT2=0.5A~2.5A

200us/div

Rev.1.0
7 / 13

ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com■Detailed description

ELM615DA is a constant on-time controlled synchronous step-down converter with 4V to 36V input voltage
range. The device can provide up to 5A continuous output current. Output voltage is set by an external resistor
divider with feedback point connected to FB pin.
1. CC/CV mode control
ELM615DA operates in either Constant Voltage (CV) mode or Constant Current (CC) mode depends on loadcondition. When channel 1 and channle2 output current is below constant current threshold, ELM615DA regulates output voltage in CV mode. As Channel 1 or Channel 2 output current increases and reaches the ConstantCurrent threshold, ELM615DA enters CC mode and by reducing output voltage and maintaining relative channel output current constant. Once FB pin voltage falls below 0.4V, the regulated channel current level will linearly fold back as FB voltage continues to drop.
2. Spread-spectrum option
ELM615DA has an internal spread-spectrum option to optimize EMI performance. The modulation signal isa triangular wave with a period of 340us at 180kHz. Therefore, switching frequency will linearly vary between
180kHz -6% to 180kHz every 330us.
3. Internal soft-start
ELM615DA has built-in 3ms soft-start. During the soft start period, output voltage is ramped up linearly to theregulation voltage, independent of the load current level and output capacitor value.
4. Output over current protection
ELM615DA has cycle-by-cycle HS current limit protection to prevent inductor current from running away.
Once HS current limit is triggered, ELM615DA will turn on LS and wait for the inductor to drop down to a predetermined level before the HS can be turned on again. If this current limit condition is repeated for a sustained
long period of time, ELM615DA will consider it as over-load or short circuit. Either way, ELM615DA will enterhiccup mode, where it stop switching for a pre-determined period of time before automatically re-try to start up
again. It always starts up with soft-start to limit inrush current and avoid output overshoot.

Rev.1.0
8 / 13

ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com■Application information
1. Setting output voltage

The output voltage is set using the FB pin and a resistor divider connected to the output as shown in AP Circuit
below. The output voltage (VOUT) can be calculated according to the voltage of the FB pin (VFB=0.8V Typical),Thus the output voltage is:
R1
VOUT = VFB × (+1)
R2
2. Programmable cable compensation
ELM615DA provides programmable cable compensation by selecting appropriate external feedback resistor
divider to compensate resistive voltage drop over the chargers’ output cable. The cable compensation voltage
can be expressed as
IFB × R1 = IOUT × RCABLE∆VOUT = 2.5μA ×

IOUT
× R1
5A

IOUT is equal to sum of channel 1 and channel 2 output current.
3. Setting the channel 1 and 2 CC current
ELM615DA channel 1 constant current value is set by the resistor RIS1 connected between the IS1 and GND
pins. Channel 2 constant current value is set by the resistor RIS2 between the IS2 and GND pins. The CC current
is determined by the equation as follows
ICS1 = 60mV/RIS1
ICS2 = 60mV/RIS2
4. Input capacitor selection
The input capacitor must sustain the ripple current produced during the period of “ON” state of the high side
MOSFET, so a low ESR ceramic capacitor is required to minimize the loss. The input ripple current RMS value
can be calculated by the following equation:
IINRMS = IOUT √ D × (1- D)
Where D is the duty cycle, lINRMS is the input RMS current, and IOUT is the load current. The equation reaches
its maximum value with D = 0.5. The loss of the input capacitor can be calculated by the following equation:
PCIN = ESRCIN × IINRMS2
Where PCIN is the power loss of the input capacitor and ESRCIN is the effective series resistance of the input capacitance. Due to large di/dt through the input capacitor, low ESR ceramic capacitors should be used.
Depending on the application, additional capacitors may be required to improve input ripple current, transient
response characteristics, and EMI characteristics. The value of CIN is determined in relation to the power supply
impedance. If the power supply impedance is high, a large input capacitor is required. The input capacitor mustwithstand a voltage equal to or greater than the maximum input voltage.

Rev.1.0
9 / 13

ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com
5. Inductor selection
The inductor is chosen to meet the requirements of the output voltage ripple and the load transient response.
The higher inductance can reduce the inductor’s ripple current and lower output ripple voltage. Use an inductor
with a DC current rating of at least 25% percent higher than the maximum load current for most applications.
For highest efficiency, select an inductor with a DC resistance less than 15mΩ. The inductor ripple current andoutput voltage ripple is approximated by the following equations:∆I =VIN - VOUT VOUT
VOUT × ( VIN - VOUT), L=・
FS × L
VIN
VIN × FS × ∆I

IL_MAX = ILOAD +∆I, ∆VOUT = ∆I × ESR
2

Although the increase of the inductance reduces the ripple current and voltage, it contributes to the decrease of
the response time for the regulator to load transient. The way to set a proper inductor value is to have the ripple
current (∆I) be approximately 20%~50% of the maximum output current. Once the value has been determined,
select an inductor capable of carrying the required peak current without going into saturation. It is also important to have the inductance tolerance specified to keep the control accuracy of the system. 20% tolerance (atroom temperature) is reasonable for the most inductor manufacturers. For some types of inductors, especiallythose with ferrite core, the ripple current will increase abruptly when it saturates, which will result in larger output ripple voltage. Use a larger inductance for improved light-load efficiency.
6. Output capacitor selection
An output capacitor is required to filter the output and supply the load transient current. The high capacitor value and low ESR will reduce the output ripple and the load transient drop. In typical switching regulator design,the ESR of the output capacitor bank dominates the transient response. The number of output capacitors can be
determined by the following equations:∆VESR
ESRMAX =∆IOUT
Number of capacitors =ESRCAPESRMAX∆VESR = change in output voltage due to ESR∆IOUT = load transient
ESRCAP = maximum ESR per capacitor (specified in manufacturer’s data sheet)
ESRMAX = maximum allowable ESRHigh frequency decoupling capacitors should be placed as closely to the power pins of the load as physicallypossible. For the decoupling requirements, please consult the capacitor manufacturers for confirmation.
7. Layout consideration
To ensure stable, high efficiency and low noise operation of the power converter system, the PCB layout isa critical step. Due to high current and voltage slew rate, several signal paths need to be carefully designed tominimize stray inductance and parasitic capacitance that could generate noise and degrade performance. Followings are the layout guidelines:(1) The loop (VIN-SW-L-COUT-GND) carries high current. The traces within this loop should be kept as wide
Rev.1.0
10 / 13

ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com
and short as possible to reduce parasitic inductance and high-frequency loop area. It is also good for efficiency
improvement.
(2) Place Input capacitor as close as possible to the IC Pins (VIN and GND) and the input loop area should be as
small as possible to reduce parasitic inductance, input voltage spike and noise emission.
(3) Feedback components (R1, R2, RT and CFF) should be routed as far away from the inductor and the BST andSW pins to minimize noise coupling.
(4) A Ground plane using one PCB layer is recommended for stable operation with low ground impedance.

■ELM615DA car charger application schematic
VIN

4V~36V

Cin1 Cin2
100uF 10uF

Cin3
0.1uF
Cvcc
1uF

VIN

BST

VCC

Cbst
100nF
L 22uH

Vout

SW

ELM615DA
MT3901

AGND
PGND
EP

Co1
10uF

Co2 R1
220uF 240k

~120mΩ
USB Cable 1

Cff
1nF

USB1
5V/2.4A

FB

R2
45.3k

RS1
25mΩ

IS2

IS1

RS2
25mΩ
USB Cable 2

Vout~120mΩ

5V/2.4A

USB2

Fig-2. Typical application circuit for 5V/4.8A dual-output car charger

EVB BOM list
Qty
1

Ref
CIN1

Value
100μF

Description
Electrolytic capacitor, 50V

Package
EC 8×12mm

1
1

CIN2
CIN3

10μF
0.1μF

Ceramic capacitor, 50V, X5R
Ceramic capacitor, 50V, X5R

0603
0603

1

COUT1

10μF

Ceramic capacitor, 50V, X5R

0805

1
1
1

COUT2
CBST
CVCC

220μF
100nF
1μF

Solid-state capacitor
Ceramic capacitor, 16V, X5R
Ceramic capacitor, 10V, X5R

8×12mm
0603
0603

1
2
1

L
RS1, RS2
R1

100%22μH

25mΩ
240KΩ

Inductor
Ceramic capacitor, 10V, X5R
Resistor, ±1%

SMD
1206
0603

1
1
1

R2
RCABLE
CFF

94%

45.3KΩ
120mΩ
92% 1nF

Resistor, ±1%
Resistor, ±1%
Ceramic Capacitor, 10V, X5R

0603
0805
0603

1

Power ICELM615DA
90%

Step-down DC/DC converter

Efficiency(%)

98%
96%

E f f iciency

88%

24Vin5Vo

Rev.1.0

12Vin9Vo

86%
84%

SOP-8
12Vin5Vo

24Vin9Vo

11 / 13
0.01

0.1

Io(A)

1

10

ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com■Marking

Mark
MT3901

Content
Product ID : ELM615DA

a to eAssembly lot number■SOP-8 Package information
L

D

e

A1

b

Symbols
SYMBOLS
A

A1
A
D
A1
E1
D
D1
E1
E2
D1
E
E2
L
bE
eL
b
e

A

E

E2

E1

D1

Millimeters

InchesMin.
Max.
MILLIMETERS
1.35
1.75
MIN.
MAX.
0.00
0.15
1.35
1.75
4.70
5.10
0.00
0.15
3.70
4.10
4.7
5.1
2.90
3.50
3.7
4.1
2.00
2.50
2.90
3.50
5.80
6.20
2.00
2.50
0.40
1.27
5.80
6.20
0.31
0.51
0.40
1.27
1.16
1.37
0.31

0.51

1.16

1.37

Min.
INCHES
0.053
MIN.
0.000
0.053
0.185
0.000
0.145
0.185
0.114
0.145
0.080
0.114
0.228
0.080
0.016
0.228
0.012
0.016
0.046

Max.
0.069
MIN.
0.006
0.069
0.200
0.006
0.161
0.200
0.138
0.161
0.098
0.138
0.244
0.098
0.050
0.244
0.020
0.050
0.054

0.046

0.054

0.012

0.020

Rev.1.0
12 / 13

ELM615DA

36V 5A synchronous Step-down converter with dual-channel current limit
https://www.elm-tech.com■SOP-8 Carrier tape & reel dimensions• Orientation/carrier tape information
A

C

A

B

B

C

D

D

Feeding direction
Feeding direction

2. Reel Information:• Reel information
2. Reel Information:• Dimension details
3.

Dimension Details:

3. typeDimension A
Details:
PKG

SOP-8

4.0 mmPKG Type
PKG Type
SOP8EPSOP8EP

B

C

1.5 mm

12.0 mm

A

A
4.0 mm
4.0 mmB

B
1.5 mm
1.5 mmDC

8.0 mmC
12.0 mm12.0 mmE
D

F

13 inchesD
8.0 mm
8.0 mmE

Q'ty/Reel

13.0 mmE
13 inches
13 inches

FF
13.0 mm13.0 mm2,500

Q'ty/Reel
Q'ty/Reel
2,500
2,500

Rev.1.0
13 / 13