ELM ELM620BA Schematics

1

Rev.1.0

Parameter Symbol Limit Unit
VIN power supply voltage Vin -0.3 to +6.0 V
Apply voltage to SW Vsw GND-0.3 to Vout+0.3 V
Apply voltage to FB Vfb GND-0.3 to Vout+0.3 V
Apply voltage to EN Ven GND-0.3 to Vout+0.3 V
Apply voltage to VOUT Vout -0.3 to +6.0 V
Power dissipation Pd 250 mW
Operating temperature range Top -30 to +85 °C
Storage temperature range Tstg -65 to 125 °C

■General description

■Features

■Maximum absolute ratings

• Cellular phone

• Digital camera

• MP3 player

• Portable machine

• Wireless handset

■Application

10 -

• 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

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 .

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

*

Taping direction is one way.

ELM620BA-S

Symbol

a Package B: SOT-26
b Product version A
c Taping direction S: Refer to PKG file

ELM620BA - S

↑ ↑

↑

a b

c

■Selection guide

ELM620BA

1.4MHz

high efficiency synchronous PWM step up DC/DC converter

2

Rev.1.0

■Pin assignment

1) 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 :

Vout = 1.203V × (1 +

R1

)

R2

4) 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 operation
is started, it is completely independent from Vin and only limited by output power level and battery’s internal
series resistance.

SOT-26(TOP VIEW)

1

2

3

6

5

4

■Pin configuration

Pin No. Pin name Pin description

1 SW Switch
2 GND Ground
3 FB Feedback
4 EN ON/OFF control (High enable)
5 VOUT Output
6 VIN Input

10 -

ELM620BA

1.4MHz

high efficiency synchronous PWM step up DC/DC converter

3

Rev.1.0

■Block diagram



+



+






+

optional

EN

SW

Vin

FB

Vout

GND

Optional

schottky

L

2.2µH

Cin

22µF

1V to 5V

Input

Vout

1.203V
ref

R1

1.02M
1%

R2
604k
1%

Cff

Cout
22µF

0.45Ω

0.35Ω

Current
sense

g

m
error

AMP

PWM
comp

PWM

control

Slope
comp

Sync drive
control

Ramp Gen

1.4MHz

Shutdown
control

Shutdown

ELM620BA

Start-up

OSC

A/B MUX

A

B

2.3V

Rc
80k

Cp

2

2.5pF

Cc
150pF

Vout
good

■Standard circuit

+

FB

VOUT

GND

VIN

ELM620BA

Vin

Optional

schottky

Vout

SW

EN

ON/OFF

L=2.2µH

Cin=
22µF

Cout
22µF

R1=

1.02MΩ

1%

R2
604k

Ω

1%

R1

Vout=(1+ )×1.203

R2

10 -

ELM620BA

1.4MHz

high efficiency synchronous PWM step up DC/DC converter

4

Rev.1.0

Parameter Symbol Condition Min. Typ. Max. Unit
Output voltage range (adj.) Vout 2.5 6.0 V
Minimum start-up voltage Vst Iload=1mA 0.9 1.1 V
Minimum operating voltage Vin EN=Vin 0.60 0.75 V
Switching frequency Fsw 1.1 1.4 1.7 MHz
Maximum duty cycle Dmax Vfb=1.15V 80 87 %
Current limit delay to output tllimdly 40 ns
Feedback voltage Vfb 1.165 1.203 1.241 V
Feedback input current Ifb Vfb=1.22V 1 nA
NMOS switch leakage IleakN Vsw=5V 0.1 5.0 µA
PMOS switch leakage

IleakP

Vsw=0V 0.1 5.0 µA

NMOS switch ON resistance

RswN

Vout=3.3V 0.35 Ω

PMOS switch ON resistance

RswP

Vout=3.3V 0.45 Ω
NMOS current limit IlimN 700 950 mA
Quiescent current (Active) Iq Measured on Vout, Non-switching 300 500 µA
Shutdown current Is Ven=0V, Including switch leakage 0.1 1.0 µA
EN input high Venh 1 V
EN input low Venl 0.35 V
EN input current Ien Ven=5.5V 0.01 1.00 µA

■Electrical characteristics

Vin=1.2V, Vout=3.3V, Top=25°C, unless otherwise noted

10 -

■Test circuits

V

I

N

S

W

F

B

L

=

2

.

2

µ

H

E

N

G

N

D

E

L

M

6

2

0

B

A

V

O

U

T

S

B

D

R

2

R

1

R

L

V

o

u

t

C

i

n

=

2

2

µ

F

V

i

n

C

o

u

t

=

2

2

µ

F

ELM620BA

1.4MHz

high efficiency synchronous PWM step up DC/DC converter