IMP2525
Application Information
Supply Filtering
IMP strongly recommends the use of a 0.1µF to 1µF bypass capac-
itor to control transients on the power supply pin. This capacitor,
connected from IN to GND, should be in close proximity to the
IMP2525 for maximum transient suppression. The lack of suitable
bypassing can result in ringing on the IN input when transients
occur. This ringing, due to supply lead inductance, could damage
IMP2525 control circuitry if the 8V maximum input rating is
exceeded.
4.0V to 5.5V
Enable Input
As with any logic input, the enable pin, EN, must be driven to a
definitive logic state at all times. Floating the input can result in
spurious operation. Do not drive EN below GND.
Fault Flag Output
Soft Start
The IMP2525 provides a “Soft-Start” function that ramps up the
ON-current to eliminate any excessive voltage drop that could
occur due to charging a capacitive load in bus-powered applica-
tions. The "Soft-Start" results from a switch ON resistance, R
ON
,
that is ramped down from a high impedance to 0.14Ω in millisec-
onds. This R
ON
ramping reduces the inrush current and related
transients occur when charging capacitive loads; a requirement
for meeting the USB voltage drop standards for bus-powered
applications (see
Figure 2).
In circuits with large load capacitances,
C
BULK
, exceeding 10µF, the soft-start circuit shown in
Figure 3
can
be used to limit the inrush start-up current to USB transient spec-
ifications. The current limiting feature of the IMP2525 provides
this high-load, soft-start operation.
IMP2525
IN
3
GND
7
0.1µF to 1µF
2525_04.eps
Figure 1. Supply Bypassing
USB
Controller
IMP2525-xBM
V
BUS
1
2
3
USB
Host
4.7µF
GND
Cable
Bus Powered Hub
Cable
Downstream USB Device
2525_06.eps
EN
FLG
GND
OUT
IN
OUT
8
7
6
Capacitive
Load
0.1µF
C
BULK
4 NC
NC 5
Figure 2. Soft-Start Application
© 2000 IMP, Inc.
USB High-Side Power Switches
5
A1PROS [ A1 PROS CO., LTD. ]
