Ver 0.9 Preliminary

Jan 25, 2002

TEL: 886-3-5788833

http://www.gmt.com.tw

8

G913

Global Mixed-mode Technology Inc.

Figure 2. Adjustable Output Using External

Feedback Resistors

Over Current Protection

The G913 use a current mirror to monitor the output cur-

rent. A small portion of the PMOS output transistor’s cur-

rent is mirrored onto a resistor such that the voltage

across this resistor is proportional to the output current.

This voltage is compared against the 1.25V reference.

Once the output current exceeds the limit, the PMOS

output transistor is turned off. Once the output transistor is

turned off, the current monitoring voltage decreases to

zero, and the output PMOS is turned on again. If the over

current condition persist, the over current protection circuit

will be triggered again. Thus, when the output is shorted

to ground, the output current will be alternating between 0

and the over current limit. The typical over current limit of

the G913 is set to 250mA. Note that the input bypass

capacitor of 1µF must be used in this case to filter out the

input voltage spike caused by the surge current due to the

inductive effect of the package pin and the printed circuit

board’s routing wire. Otherwise, the actual voltage at the

IN pin may exceed the absolute maximum rating.

Over Temperature Protection

To prevent abnormal temperature from occurring, the

G913 has a built-in temperature monitoring circuit. When

it detects the temperature is above 150

transistor is turned off. When the IC is cooled down to

below 135

the G913 will be protected against abnormal junction

temperature during operation.

Shutdown Mode

the G913 enters shutdown mode. All the analog circuits

are turned off completely, which reduces the current

consumption to only the leakage current. The output is

disconnected from the input. When the output has no

load at all, the output voltage will be discharged to ground

through the internal resistor voltage divider.

Operating Region and Power Dissipation

Since the G913 is a linear regulator, its power dissipation

power dissipation is given by:

chosen package to the ambient air. For surface mount

device, heat sinking is accomplished by using the heat

spreading capabilities of the PC board and its copper

traces. In the case of a SOT23-5 package, the thermal

resistance is typically 240

Minimum Footprint) [Figure 3] Refer to Figure 4 is the

G913 valid operating region (Safe Operating Area) & refer

to Figure 5 is maximum power dissipation of SOT 23-5.

The die attachment area of the G913’s lead frame is

connected to pin 2, which is the GND pin. Therefore, the

GND pin of G913 can carry away the heat of the G913

die very effectively. To improve the power dissipation,

connect the GND pin to ground using a large ground

plane near the GND pin.

Applications Information

Capacitor Selection and Regulator Stability

Normally, use a 1µF capacitor on the input and a 1µF

capacitor on the output of the G913. Larger input capaci-

tor values and lower ESR provide better supply-noise

rejection and transient response. A higher- value input

capacitor (10µF) may be necessary if large, fast tran-

sients are anticipated and the device is located several

inches from the power source.

Power-Supply Rejection and Operation from Sources

Other than Batteries

The G913 is designed to deliver low dropout voltages and

low quiescent currents in battery powered systems.

Power-supply rejection is 42dB at low frequencies. As the

frequency increases above 20kHz, the output capacitor is

the major contributor to the rejection of power-supply

noise.

When operating from sources other than batteries, im-

prove supply-noise rejection and transient response by

increasing the values of the input and output capacitors,

and using passive filtering techniques.

Load Transient Considerations

The G913 load-transient response graphs show two

components of the output response: a DC shift of the

output voltage due to the different load currents, and the

transient response. Typical overshoot for step changes in

the load current from 0mA to 100mA is 12mV. Increasing

the output capacitor's value and decreasing its ESR at-

tenuates transient spikes.

Input-Output (Dropout) Voltage

A regulator's minimum input-output voltage differential (or

dropout voltage) determines the lowest usable supply

voltage. In battery-powered systems, this will determine

the useful end-of-life battery voltage. Because the G913

use a P-channel MOSFET pass transistor, their dropout

rent.

IN

OUT

SHDN

SET

GND

G913

＋

1µF

R1

R2

C

OUT

1µF

R

L

OUTPUT

VOLTAGE

IN

OUT

SHDN

SET

GND

G913

＋

1µF

R1

R2

C

OUT

1µF

R

L

OUTPUT

VOLTAGE