Ver: 1.8

Jul 24, 2007

TEL: 886-3-5788833

http://www.gmt.com.tw

8

G914X

Global Mixed-mode Technology Inc.

Pin Description

PIN

G914A~H

G914Z

NAME

FUNCTION

1

1

IN

Regulator Input. Supply voltage can range from +2.5V to +6.0V. Bypass with 1µF to GND

2

2

GND

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

ground plane to maximize thermal dissipation.

3

3

SHDN

Active-Low Shutdown Input. A logic low reduces the supply current to less than 1µA. Connect to IN

for normal operation.

4

---

BYP

This is a reference bypass pin. It should connect external 10nF capacitor to GND to reduce

---

4

SET

Feedback Input for Setting the Output Voltage. Connect to GND to set the output voltage to

the preset output voltage. Connect to an external resistor divider for adjustable-output op-

1.25 (1 + R1/R2), Reference to Typical Application Circuit in Page 1.

5

5

OUT

Regulator Output. Sources up to 300mA. Bypass with a 4.7µF, ＜0.2

Ω typical ESR ca-

pacitor to GND.

Detailed Description

The block diagram of the G914X is shown in Figure 1.

It consists of an error amplifier, 1.25V bandgap refer-

ence, PMOS output transistor, internal feedback volt-

age 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 voltage is equal to 1.25V.

Similarly, when the feedback voltage is less than

1.25V, the error amplifier causes the output PMOS to

conduct 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)

Alternatively, the relationship between R1 and R2 is

given by:

(2)

For the output voltage versions of G914X, the output

voltages are 2.7V for G914A, 2.8V for G914B, 3.0V for

G914C, 3.3V for G914D, and 2.5V for G914E, 2.85V

for G914F, 1.50V for G914G and 1.80V for G914H.

Figure 1. Functional Diagram

SHDN

IN

OUT

SHUTDOWN

LOGIC

1.25V

Vref

－

ERROR

AMP

＋

OVER CURRENT

PROTECT & DYNAMIC

FEEDBACK

GND

R1

R2

OVER TEMP.

PROTECT

BYP

C

BYP

SHDN

IN

OUT

SHUTDOWN

LOGIC

1.25V

Vref

－

ERROR

AMP

＋

OVER CURRENT

PROTECT & DYNAMIC

FEEDBACK

GND

R1

R2

OVER TEMP.

PROTECT

BYP

C

BYP