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6 of 9

SS8028

BLOCK DIAGRAM

APPLICATIONS INFORMATION

The SS8028 is a boost converter with an integrated

N-channel MOSFET (refer to the block diagram above).

The boost cycle is initiated when the FB pin voltage drops

below 1.2V and the MOSFET turns on. During the period

that the MOSFET is on, the inductor current ramps up

until the 350mA current limit is reached. Then the

MOSFET turns off and the inductor current flows through

the external schottky diode, ramping down to zero.

During the MOSFET off period, the inductor current

charges the output capacitor and the output voltage

climbs. This pumping mechanism continues cycle by

cycle until the FB pin voltage exceeds 1.2V and the

non-switching mode starts. In this mode, the SS8028

consumes as little as 20uA typically, saving on battery

power.

Choosing an Inductor

There are several recommended inductors that work

well with the SS8028 in Table 1. Use the equations

and recommendations in the next few sections to find

the proper inductance value for your design.

PART

VALUE(uH)

MAX DCR ?

Ω)

VENDOR

LQH3C4R7

LQH3C100

LQH3C220

4.7

10

22

0.26

0.30

0.92

Murata

www.murata.com

CD43-4R7

CD43-100

CDRH4D18-4R7

CDRH4D18-100

4.7

10

4.7

10

0.11

0.18

0.16

0.20

Sumida

www.sumida.com

DO1608-472

DO1608-103

DO1608-223

4.7

10

22

0.09

0.16

0.37

Coilcraft

www.coilcraft.com

Inductor Selection – Boost Regulator

The appropriate inductance value for the boost regulator

application may be calculated from the following

equation. Select a standard inductor close to this value.

L =

+

+

VREF

BIAS

SHUTDOWN

LOGIC

C2

SW

L1

SHDN

VCC

C1

R1

R2

VOUT

FB

ERROR

COMP

1.2 V

en _sw

GND

PUMP CONTROL

OC

COMP

DRIVER

CONTROL

+

+

VREF

BIAS

SHUTDOWN

LOGIC

C2

SW

L1

SHDN

VCC

C1

R1

R2

VOUT

FB

ERROR

COMP

1.2 V

en _sw

GND

PUMP CONTROL

OC

COMP

DRIVER

CONTROL

Rev.2.02 12/06/2003