Ver 0.0 Preliminary

Mar 27, 2001

TEL: 886-3-5788833

http://www.gmt.com.tw

5

G920

Global Mixed-mode Technology Inc.

Pin Description

PIN

NAME

FUNCTION

1

NC

This is a NC pin, should be left unconnected.

2

IN

Regulator Input. Supply voltage can range from +2.5V to +6.5V. Bypass with 1µF to GND.

3

OUT

Regulator Output. Sources up to 150mA. Bypass with a 1µF, ＜0.2

Ω typical ESR capacitor to

GND.

4

EN

Active-High Enable Input. A logic low reduces the supply current to less than 1

µA. Connect to IN for

normal operation.

5,6,7,8

GND

Ground. This pin also functions as a heatsink. Solder to large pads or the circuit board ground

plane to maximize thermal dissipation.

Detailed Description

The block diagram of the G920 is shown in Figure 1. It

consists of an error amplifier, 1.25V bandgap refer-

ence, PMOS output transistor, internal feedback

voltage divider, shutdown logic, over current protection

circuit, and over temperature protection circuit.

The internal feedback voltage divider’s central tap is

connected to the non-inverting input of the error ampli-

fier. The error amplifier compares non-inverting input

with the 1.25V bandgap reference. If the feedback

voltage is higher than 1.25V, the error amplifier’s out-

put becomes higher so that the PMOS output transis-

reduces the current carrying capability of the PMOS

output transistor, as a result the output voltage de-

creases until the feedback v41oltage is equal to 1.25V.

Similarly, when the feedback voltage is less than

1.25V, the error amplifier causes the output PMOS to

conductor more current to pull the feedback voltage up

to 1.25V. Thus, through this feedback action, the error

amplifier, output PMOS, and the voltage divider effec-

tively form a unity-gain amplifier with the feedback

voltage force to be the same as the 1.25V bandgap

the following equation:

(1)

For the G920, the pre-set output voltage is 3.3V.

Figure 1. Functional Diagram

EN

IN

OUT

SHUTDOWN

LOGIC

1.25V

Vref

－

ERROR

AMP

＋

OVER CURRENT

PROTECT & DYNAMIC

FEEDBACK

GND

R1

R2

OVER TEMP.

PROTECT

EN

IN

OUT

SHUTDOWN

LOGIC

1.25V

Vref

－

ERROR

AMP

＋

OVER CURRENT

PROTECT & DYNAMIC

FEEDBACK

GND

R1

R2

OVER TEMP.

PROTECT