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G9611BP1U

Low-Dropout, 300mA Linear Regulator with Reset

Global Mixed-mode Technology Inc 

Global Mixed-mode Technology Inc.

G9611

Shutdown

A low input on the SHDN pin shuts down the G9611.

In the off mode, the pass transistor, regulator control

circuit are turned off, Only reset function is turned on,

reducing the supply current below 140µA. SHDN

should be connected to VIN for normal operation.

Use a fast comparator, Schmitt trigger, or CMOS or

TTL Logic to drive the SHDN pin in and out of shut-

down. Rise times should be shorter than 1µs. Do not

use slow RC circuits, leave SHDN open, or allow the

input to linger between thresholds.

Foldback Current Limiting

The G9611 also include a foldback current limiter. It

monitors and controls the pass transistor’s gate volt-

age, estimating the output current and limiting it to

900mA for output voltages above 0.78V. If the output

voltage drops below 0.78V, implying a short-circuit

condition, the output current is limited to 400mA.

Thermal Overload Protection

Thermal overload protection limits total power dissipa-

tion in the G9611. When the junction temperature ex-

ceeds TJ = +160°C, the thermal sensor sends a signal

to the shutdown logic, turning off the pass transistor

and allowing the IC to cool. The thermal sensor will

turn the pass transistor on again after the IC’s junction

temperature cools by 30°C, resulting in a pulsed out-

put during thermal overload conditions.

Thermal overload protection is designed to protect the

G9611 in the event of fault conditions. For continual

operation, the absolute maximum junction temperature

rating of TJ = +160°C should not be exceeded.

Operating Region and Power Dissipation

Maximum power dissipation of the G9611 depends on

the thermal resistance of the case and circuit board,

the temperature difference between the die junction

and ambient air, and the rate of air flow. The power

dissipation across the device is P = IOUT (VIN-VOUT).

The resulting maximum power dissipation is:

PMAX=

(TJ-TA)

(θJC+θCA)

where (TJ -TA) is the temperature difference between

the G9611 die junction and the surrounding air, θJC is

the thermal resistance of the package chosen, and θCA

is the thermal resistance through the printed circuit

board, copper traces and other materials to the sur-

rounding air. The thermal resistance of SOP-8 is θJC

= 192°C/W.

The power dissipation of G9611 is:

PD = (VIN - VOUT) x IOUT

The worst-case thermal resistance from case to air

(θCA) requirements are:

θCA =

(125°C -TA)

PD

Use larger copper pad area to obtain specific heat sink

thermal resistance values for larger output current,

higher input-output difference, and higher ambient

temperature.

CD Capacitor Selection

The reset timeout delay is set by internally pull-up RD

(typical value 200kΩ) and external CD.

When the voltage at CD pin exceeds the buffer thresh-

old, typically 0.8 VCC, the RESET output high. The

voltage detector and buffer have built-in hysterisis to

prevent erratic reset operation. For CD = 0.1µF, typical

reset time delay is 30ms. The formula of delay time is:

T(ms) = 303 x CD(µF)

Regulator Output Capacitor Selection and Regu-

lator Stability

Normally, use capacitors 0.1µF minimum on the input

and 10µF minimum on the output of the G9611. The

larger input capacitor values provide better supply noise

rejection and line-transient response. Improve load tran-

sient response, stability, and power-supply rejection by

using large output capacitors. For stable operation over

the full temperature range and with load current up to

300mA, 10µF tantalum or 47µF aluminum minimum is

recommended. Too small capacitors with small ESR

can result in oscillation.

Transient Considerations

The Typical Operating Characteristics show the

G9611 load-transient response. Two components of

the output response can be observed on the

load-transient graphs—a DC shift from the output im-

pedance due to the different load currents, and the

transient response. Typical transients for step changes

in the load current from 5mA to 500mA are 0.1V. In-

creasing the output capacitor’s value attenuates tran-

sient spikes.

Ver: 1.4

Jun 29, 2004

TEL: 886-3-5788833

http://www.gmt.com.tw

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