G526-1 datasheet(4/6 Pages) ETC

4 / 6 page

Ver 1.0

Dec 26, 2000

TEL: 886-3-5788833

http://www.gmt.com.tw

G526

Global Mixed-mode Technology Inc.

Undervoltage Lockout

UVLO (undervoltage lockout) prevents the output

MOSFET from turning on until IN (input voltage) ex-

ceeds 2.5V typical. After the switch turns on, if the

voltage drops below 2.3V typical, UVLO shuts off the

output MOSFET and signals the fault flag. Undervolt-

age detection functions only when at least one switch

is enabled.

Current Sensing and Limiting

The current limit threshold is preset internally. The

preset level prevents damage to the output MOSFET

and external load but allows a minimum current of

0.5A through the output MOSFET.

A current sense circuit senses the output current of

MOSFET switch. If output current exceeds the current

limit threshold, the output MOSFET switch is shut off

and a fault flag is pulled low. The reaction to an over-

current is measured with the following scenarios:

Switch Enable into Heavy Load

If a switch is powered-on or enabled into a heavy load

or short-circuit, the switch immediately goes into a

constant-current mode, reducing output voltage. The

fault flag goes low until the load is reduced or thermal

shutdown occurs.

Heavy Load Applied Suddenly to Enabled Switch

When a heavy load is applied, a large current may

flow from the output capacitor and the switch. The

current limit circuit may shut the switch off briefly, then

fold back into constant-current mode. In that case, the

fault flag falls until the load is reduced.

Fault Flag

FLG is an N-channel, open-drain MOSFET output.

The fault-flag is active (low) for one or more of the

following conditions: undervoltage, current limit, or

thermal shutdown. The flag output MOSFET is capa-

ble of sinking a 10mA load to typically 100mV above

ground.

Both flag pins may be "wire-NORed" to a

common pullup resistor.

Applications Information

Supply filtering

A 0.1µF to 1µF bypass capacitor from IN to GND, lo-

cated at the G526, is strongly recommended to control

supply transients. Without a bypass capacitor, an out-

put short may cause sufficient ringing on the input

(from supply lead inductance) to damage internal con-

trol circuitry.

Input or output transients must not exceed the abso-

lute maximum supply voltage (VIN max = 6V) even for

a short duration.

Figure 1. Supply Bypassing

Figure 2. Soft Start (Single Channel)

ENA

FLGA

FLGB

ENB

OUTA

GND

OUTB

G526

4.0V to 5.5V

0.1µF to 1µF

USB Host

GND

BUS

Cable

Bus Powered Hub

USB

Controller

BULK

4.7

µF

G526

Cable

Downstream USB Device

Capacitive

Load

OUTA

GND

OUTB

ENA

FLGA

FLGB

ENB

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