
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.
Ver 1.0
Dec 26, 2000
TEL: 886-3-5788833
http://www.gmt.com.tw
4
G526
Global Mixed-mode Technology Inc.
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 0.1
μ
F to 1
μ
F 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
IN
GND
OUTB
G526
4.0V to 5.5V
0.1μF to 1μF
USB Host
GND
V
BUS
Cable
Bus Powered Hub
USB
Controller
C
BULK
4.7
μF
G526
Cable
Downstream USB Device
Capacitive
Load
1
2
3
4
8
7
6
5
OUTA
IN
GND
OUTB
ENA
FLGA
FLGB
ENB