ELM620BA 1.4MHz

high efficiency synchronous PWM step up DC/DC converter
https://www.elm-tech.com■General description

ELM620BA is synchronous PWM step-up DC/DC converter with high efficiency and 1.4MHz fixed frequency;
by adopting synchronous switch, ELM620BA is able to provide high efficiency without external Schottky diode.
ELM620BA is able to activate within the range from 0.6V to 5V of input voltage and 2.5V to 6V of output one.
For 3V or 3.3V output, ELM620BA can provide current up to 260mA by a single AA cell, or to 600mA by 2
serial-connected AA cells.
With 1.4MHz switching frequency, small coils and capacitors can be adopted; therefore, ELM620BA is possible
to be assembled within small areas on the board .

■Features■Application• Current mode control• Output voltage drop protection• Thermal shutdown protection and short circuit protection• Input voltage: 0.6V to 5.0V
• Output voltage: 2.5V to 6.0V
• Low current consumption: Typ.300µA• Shutdown current: < 1µA• Low start-up voltage: Typ.0.9V• Low switch on (internal switch) resistance : 0.35Ω
• Constant frequency: Typ.1.4MHz• High efficiency: 96%• Package: SOT-26• Cellular phone• Digital camera• MP3 player• Portable machine• Wireless handset■Maximum absolute ratings
Parameter
VIN power supply voltage
Apply voltage to SW
Apply voltage to FB
Apply voltage to EN
Apply voltage to VOUT
Power dissipation
Operating temperature range
Storage temperature range

SymbolVinVsw
Vfb
VenVout
PdTopTstg

Limit-0.3 to +6.0
GND-0.3 to Vout+0.3
GND-0.3 to Vout+0.3
GND-0.3 to Vout+0.3-0.3 to +6.0
250
-30 to +85-65 to 125

Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used.

UnitVVVVVmW°C°C■Selection guide

ELM620BA-S
Symbolabc

Package
Product version
Taping direction

B: SOT-26
A
S: Refer to PKG file

ELM620BA - S↑↑ ↑ab c* Taping direction is one way.

Rev.1.0
1 / 10ELM620BA 1.4MHz
high efficiency synchronous PWM step up DC/DC converter

https://www.elm-tech.com■Pin configuration
SOT-26(TOP VIEW)

Pin No.
123456Pin nameSWGND
FBENVOUT
VIN

Pin description

SwitchGroundFeedback
ON/OFF control (High enable)
OutputInput■Pin assignment1) SW (Pin 1) : Switch pin.
Connect inductor between SW and VIN. Keep these PCB trace lengths as short and wide as possible to reduce
EMI and voltage overshoot.
2) GND (Pin 2) : Signal and power ground.
Provide a short direct PCB path between GND and the (−) side of output capacitor(s).
3) FB (Pin 3) : Feedback input to gm error amplifier.
Connect resistor divider tap to this pin. The output voltage can be adjusted from 2.5V to 6V by :R1Vout = 1.203V × (1 +)R24) EN (Pin 4) : Logic controlled shutdown input.
EN = High: Normal free running operation, 1.4MHz typical operating frequency. EN = Low: Shutdown, quiescent current < 1μA. Output capacitor can be completely discharged through the load or feedback resistors.
5) VOUT (Pin 5) : Output voltage sense input and drain of internal synchronous rectifier MOSFET.
Bias is derived from Vout. PCB trace length from Vout to output filter capacitor(s) should be as short and wide
as possible.
6) VIN (Pin 6) : Battery input voltage.
The device gets its start-up bias from Vin. Once Vout exceeds Vin, bias comes from Vout. Thus, once operationis started, it is completely independent from Vin and only limited by output power level and battery’s internal
series resistance.

Rev.1.0
2 / 10ELM620BA 1.4MHz
high efficiency synchronous PWM step up DC/DC converter

https://www.elm-tech.com■Standard circuit
Optional
schottky

L=2.2µH

Vin+Cin=22µF

SW
VINVout

VOUTR1=1.02MΩ

ELM620BA
EN

ON/OFF

1%FB

Cout
22µF

R2604kΩ1%

GND

Vout=(1+R1)×1.203
R2■Block diagram
L
2.2µH

Cin
22µF

1V to 5V
Input

Optional
schottky

Vin
Vout
good
Start-up
OSC

Ramp Gen
1.4MHz

A

SW+�

2.3V

ELM620BA

Vout

A/B MUX

PWM
control

Sync drive
control

Slope
comp�

0.35Ω
Cff
optional

Cout
22µF

gm � FB

Rc
80k

Shutdown

R1
1.02M
1%

Current
sense+

Shutdown
control

Vout

B

PWM
�comp �EN

0.45Ω

Cc
150pF

error
AMP +Cp2
2.5pF

1.203Vref

R2604k1%

GND

Rev.1.0
3 / 10ELM620BA 1.4MHz
high efficiency synchronous PWM step up DC/DC converter

https://www.elm-tech.com■Electrical characteristics
Parameter
Output voltage range (adj.)
Minimum start-up voltage
Minimum operating voltage
Switching frequency
Maximum duty cycle
Current limit delay to output
Feedback voltage
Feedback input current
NMOS switch leakage
PMOS switch leakage
NMOS switch ON resistance
PMOS switch ON resistance
NMOS current limit
Quiescent current (Active)
Shutdown current
EN input highEN input low
EN input currentVin=1.2V, Vout=3.3V, Top=25°C, unless otherwise noted
SymbolCondition
Min.
Typ.
Max. Unit
Vout
2.5
6.0VVstIload=1mA
0.9
1.1
V
Vin
EN=Vin
0.60
0.75
VFsw
1.1
1.4
1.7 MHz
Dmax Vfb=1.15V
80
87%tllimdly
40
nsVfb
1.165 1.203 1.241
VIfb
Vfb=1.22V
1nA
IleakN Vsw=5V
0.1
5.0µA
Vsw=0V0.1
5.0µA
IleakP
0.35
Ω
RswN Vout=3.3V
Vout=3.3V
0.45
ΩRswP
IlimN
700950mA
Iq
Measured on Vout, Non-switching
300
500µAIsVen=0V, Including switch leakage
0.1
1.0
µA
Venh1VVenl
0.35
VIen
Ven=5.5V
0.01
1.00
µA

■Test circuits

SWVIN

VOUT

ELM620BAFBENGND

Rev.1.04 / 10

ELM620BA 1.4MHz
high efficiency synchronous PWM step up DC/DC converter

https://www.elm-tech.com■Application notes

1) PCB layout guidelines
The high speed operation of ELM620BA demands careful attention to board layout, and in order to get advertised performance, a well-planned layout is required. Figure-1 is an example which shows the recommended
component placement with optional Schottky diode. A large ground pin copper area will help to lower the chiptemperature. A multilayer board with a separate ground plane is ideal, but not absolutely necessary.
Fig-1

Vin1

SWVIN

62

GND VOUT

53

FB

4EN

EN

VoutFigure 1: Recommended component placement for single layer board with optional Schottky diode. Traces carrying high current are direct. Trace area at FB pin is small. Lead length to battery is short.
2) Inductor selection
ELM620BA can utilize small surface mount and chip inductors due to its fast 1.4MHz switching frequency.
Typically, a 2.2μH inductor is recommended for most applications; larger values of inductance will allow greater output current capability by reducing the inductor ripple current. Increasing the inductance above 10μH will
increase size while providing little improvement in output current capability.
Iout(max) = η × (Ip −Vin×D) × (1 − D)
2×f×L

where:

η = estimated efficiency
Ip = peak current limit value (0.7A)
D = steady-state duty ratio = (Vout − Vin) / VoutVin = input (battery) voltage
f = switching frequency (1.4MHz typical)
L = inductance value
The inductor current ripple is typically set for 20% to 40% of the maximum inductor current (IP). High frequency ferrite core inductor materials reduce frequency dependent power losses compared to cheaper powderediron types. The inductor should have low ESR (series resistance of the windings) to reduce the I2R power losses,
and must be able to handle the peak inductor current without saturating. Molded chokes and some chip inductors usually do not have enough core to support the peak inductor currents of 950mA seen on ELM620BA. To
minimize radiated noise, ELM recommends using a toroid, pot core or shielded bobbin inductor. See Table forsome suggested components and suppliers.
Table : Recommended inductors.
LPart(μH)
CDRH3D162.2
CDH3B162.2

Max. DCR(mΩ)
7570

Max. DC current
(A)
1.2
1.2

Size: W × L × H(mm3)
3.8×3.8×1.8
4.0×4.0×1.8Vendor
SumidaCeaiya

Rev.1.05 / 10

ELM620BA 1.4MHz
high efficiency synchronous PWM step up DC/DC converter

https://www.elm-tech.com3) Output and input capacitor selection
Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple. Multilayer ceramic capacitors are an excellent choice, as they have extremely low ESR and are available in small
footprints. A 4.7μF to 22μF output capacitor is sufficient for most applications; larger values up to 22μF may be
used to obtain extremely low output voltage ripple and improve transient response. An additional phase lead capacitor may be required with output capacitors larger than 10μF to maintain acceptable phase margin. X5R andX7R dielectric materials are preferred for their ability to maintain capacitance over wide voltage and temperature ranges.
Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. It
follows that ceramic capacitors are also a good choice for input decoupling and should be located as closely as
possible to the device. A 10μF input capacitor is sufficient for virtually any application. Larger values may beused without limitations.

■MarkingSOT-26
a to e : Assembly lot No.
A to Z (I, O, X excepted) and 0 to 9

Rev.1.06 / 10

ELM620BA 1.4MHz
high efficiency synchronous PWM step up DC/DC converter

https://www.elm-tech.com■Typical characteristics• V=3.3V• Vout=3.3V : Cin=22µF, Cout=22µF, L=2.2µH, R1=46.6kΩ, R2=26.7kΩ, Top=25°C
Vout-Vin

4.0

Vout (V)EFFICIENCY (%)

3.5 Iout=1mA

3.0100mA

2.5

EFFICIENCY-Iout

10010mA

2.01.51.080

Vin=3V60

Vin=2.4V
Vin=1.8V

40

Vin=1.5V

200.5
00.5

21.5

12.5

00.1

3100

1000

4050

Iout (mA)

Vin (V)

Vout-Iout

4101

Vhold-Iout

0.7
0.6

Vin=3V

Vhold (V)

Vout (V)3

Vin=2.4V
Vin=1.8V

2

Vin=1.5V

0.5
0.4
0.3
0.2

1110

Iout (mA)

1000.1

1000

0102030

Iout (mA)

Rev.1.07 / 10

ELM620BA 1.4MHz
high efficiency synchronous PWM step up DC/DC converter

https://www.elm-tech.com

Vout-Top

1.2

3.34

1.1

3.32

Vout (V)

Vst (V)

Vst-Iout

1.0

0.90.83.30

3.280

3.5

10203040

3.26-4050-200204060

Iout (mA)

Top (�)Start Response

Load Transient Response

Vin=Ven=1.8V, No load

Vout (V)3280

Vin=1.8V, Iout=0.1mA�0.1A

3.5
3.4
3.3

3.2

100.1

10

Iout (A)

2Ven (V)

Vout (V)Vin=1.5V, Iout=0.1A

000 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 42468 10 12 14 16 18 20

Time (ms)Time (ms)Rev.1.08 / 10

ELM620BA 1.4MHz
high efficiency synchronous PWM step up DC/DC converter

https://www.elm-tech.com• V=5.0V• Vout=5.0V : Cin=22µF, Cout=22µF, L=2.2µH, R1=68.5kΩ, R2=21.7kΩ, Top=25°C
Vout-Vin

6.0

Iout=1mAEFFICIENCY (%)

Vout (V)

5.0

4.0

100mA

3.010mA

2.0

1.0

0

0.5

1

1.5

2

EFFICIENCY-Iout

100

32.5

3.5

Vin=3V80

60

Vin=1.8V

40

2000.1

41Vin (V)

Vout-Iout

60.8

4Vhold (V)Vout (V)100

Vhold-Iout

0.9

5Vin=3V

Vin=1.8V

32110Iout (mA)

0.70.60.50.4

1100.3100

Iout (mA)

0102030

Iout (mA)

4050

Rev.1.0
9 / 10ELM620BA 1.4MHz
high efficiency synchronous PWM step up DC/DC converter

https://www.elm-tech.com

Vout-Top

Vst-Iout

1.2

5.05

Vout (V)

1.0

0.9

4.95

010

2030

40

4.90
-40

50-200204060

Iout (mA)

Top (�)Start Response

Load Transient Response

Vin=Vec=3V, No load

6Vout (V)43280

Vin=3V, Iout=0.1mA�0.1A

5.25

55.12554.87510.10321Ven (V)Vout (V)

5.000000.2

0.4

0.6

0.8

01246

Iout (A)Vst (V)1.1

0.8

Vin=3V, Iout=0.1A

5.10

8 10 12 14 16 18 20

Time (ms)Time (ms)Rev.1.0
10 / 10