Global Mixed-mode Technology Inc.
from turning on until the die temperature drops to
125°C. Thermal shutdown circuit functions only when
the switch is enabled.
Undervoltage Lockout
UVLO (undervoltage lockout) prevents the output
MOSFET from turning on until IN (input voltage) ex-
ceeds 2.5V typically. After the switch turns on, if the
voltage drops below 2.3V typically, UVLO shuts off the
output MOSFET and signals the fault flag. UVLO de-
tection functions only when the 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 Enabled into Heavy Load
If the switch is powered on or enabled into a heavy
load or short-circuit, the switch immediately goes into
a constant-current mode, reducing the output voltage.
The fault flag goes low until the load is reduced or
thermal shutdown occurs. See the "Enable into Short
Circuit" graph.
Heavy Load Applied to Enabled Switch
When a heavy load is applied, a large current may
flow from the switch. The current limit circuit may shut
the switch off briefly, then fold back into con-
stant-current mode. In that case, the fault flag falls
until the load is reduced. See the “Short Applied to
Output” graph and the "Ramped Load to Enable De-
vice" graph.
G525A
Fault Flag
FLG is a 2-channel, open-drain MOSFET output. The
fault-flag is active (low) for one or more of the follow-
ing conditions: current limiting, undervoltage, or ther-
mal shutdown. The flag output MOSFET is capable of
sinking a 10mA load to typically 100mV above ground.
Applications Information
Supply filtering
A 0.1µF to 1µF bypass capacitor from IN to GND, lo-
cated near the G525A, is strongly recommended to
control supply transients. Without a bypass capacitor,
an output short may cause sufficient ringing on the
input (from supply lead inductance) to damage internal
control circuitry.
Input transients must not exceed the absolute maxi-
mum supply voltage (V
IN max
= 6V) even for a short du-
ration.
Figure 1. Supply Bypassing
3.0V to 5.5V
G525A
1
2
3
4
EN
FLG
GND
NC
OUT
IN
OUT
NC
8
7
0.1 µF to 1 µF
6
5
USB
Controller
V
BUS
1
G525A
USB Host
4.7
µF
EN
2
FLG
3
GND
4 NC
8
OUT
7
IN
6
OUT
NC 5
0.1 µF
C
BULK
Capacitive
Load
GND
Cable
Bus Powered Hub
Cable
Downstream USB Device
Figure 2. Soft Start
Ver: 1.2
Nov 11, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
6
GMT [ GLOBAL MIXED-MODE TECHNOLOGY INC ]
