G5103T11UF データシートの表示（PDF） - Global Mixed-mode Technology Inc

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G5103T11UF

Micro-power Step-Up DC/DC Converters in SOT-23-5

Global Mixed-mode Technology Inc 

Global Mixed-mode Technology Inc.

Pin Description

G5103

PIN

NAME

FUNCTION

1

SW Switch Pin. The drain of the internal NMOS power switch. Connect this pin to inductor.

2

GND Ground.

Feedback Pin. Set the output voltage by selecting values for R1 and R2 (see Block Diagram):

3

FB

R1 = R2 VOUT -1

1.2

4

Active-Low Shutdown Pin. Tie this pin to logic-high to enable the device or tied it to logic-low to turn this

SHDN device off.

5

VCC Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible.

Function Description

The G5103 is a boost converter with a NMOS

switch embedded (refer to Block Diagram). The

boost cycle is getting started when FB pin voltage

drop below 1.2V as the NMOS switch turns on.

During the switch on period, the inductor current

ramps up until 350mA current limit is reached. Then

turns the switch off, while the inductor current flows

through external schottky diode, and ramps down to

zero. During the switch off period, the inductor cur-

rent charges output capacitor and the output volt-

age is boosted up. This pumping mechanism con-

tinues cycle by cycle until the FB pin voltage ex-

ceed 1.2V and entering the none switching mode.

In this mode, the G5103 consumes as low as 20uA

typically to save battery power.

Applications Information

Choosing an Inductor

There are several recommended inductors that work

well with the G5103 in Table 1. Use the equations and

recommendations in the next few sections to find the

proper inductance value for your design.

Table 1. Recommended Inductors

PART VALUE(µH) MAX DCR (Ω) VENDOR

LQH3C4R7

4.7

LQH3C100

10

LQH3C220

22

0.26

Murata

0.30

www.murata.com

0.92

CD43-4R7

4.7

0.11

CD43-100

10

0.18

Sumida

CDRH4D18-4R

4.7

0.16

www.sumida.com

7

10

0.20

CDRH4D18-100

DO1608-472

4.7

DO1608-103

10

DO1608-223

22

0.09

Coilcraft

0.16

www.coilcraft.com

0.37

Inductor Selection—Boost Regulator

The appropriate inductance value for the boost regu-

lator application may be calculated from the following

equation. Select a standard inductor close to this

value.

L=

VOUT-VIN(MIN)+VD

ILIM

x tOFF

Where VD = 0.4V (Schottky diode voltage), ILIM =

350mA and tOFF = 500ns. A larger value can be used

to lightly increase the available output current, but limit

it to about twice the calculating value. When too large

of an inductor will increase the output voltage ripple

without providing much additional output current. In

varying VIN condition such as battery power applica-

tions, use the minimum VIN value in the above equa-

tion. A smaller value can be used to give smaller

physical size, but the inductor current overshoot will be

occurs (see Current Limit Overshoot section).

Inductor Selection—SEPIC Regulator

For a SEPIC regulator using the G5103, the approxi-

mate inductance value can be calculated by below

formula. As for the boost inductor selection, a larger or

smaller value can be used.

L=2

VOUT + VD

ILIM

x tOFF

Current Limit Overshoot

The G5103 use a constant off-time control scheme,

the power switch is turned off after the 350mA current

limit is reached. When the current limit is reached and

when the switch actually turns off, there is a 100ns

delay time. During this time, the inductor current ex-

ceeds the current limit by a small amount. The formula

below can calculate the peak inductor current.

IPEAK = ILIM +

VIN(MAX) - VSAT x 100ns

L

Where VSAT = 0.25V (switch saturation voltage). When

the systems with high input voltages and uses smaller

inductance value, the current overshoot will be most

apparent. This overshoot can be useful as it helps in-

crease the amount of available output current. To use

small inductance value for systems design, the current

limit overshoot can be quite high. Even if it is internally

current limited to 350mA, the power switch of the

G5103 can operate larger currents without any prob-

lem, but the total efficiency will suffer. The IPEAK is keep

below 500mA for the G5103 will be obtained best per-

formance.

Ver: 1.1

Sep 20, 2004

TEL: 886-3-5788833

http://www.gmt.com.tw

5

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