IMP2525
Application Information
Supply Filtering
Enable Input
IMP strongly recommends the use of a 0.1µF to 1µF bypass capac- As with any logic input, the enable pin, EN, must be driven to a
itor to control transients on the power supply pin. This capacitor, definitive logic state at all times. Floating the input can result in
connected from IN to GND, should be in close proximity to the spurious operation. Do not drive EN below GND.
IMP2525 for maximum transient suppression. The lack of suitable
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-
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
tions. The "Soft-Start" results from a switch ON resistance, RON
,
that is ramped down from a high impedance to 0.14Ω in millisec-
onds. This RON 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,
CBULK, 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
7
IN
3
GND
0.1µF to 1µF
2525_04.eps
Figure 1. Supply Bypassing
USB
Controller
IMP2525-xBM
8
7
6
1
2
3
VBUS
EN
OUT
IN
FLG
GND
NC
Capacitive
Load
OUT
NC
USB
Host
4
5
4.7µF
0.1µF
CBULK
GND
Cable
Bus Powered Hub
Cable
Downstream USB Device
2525_06.eps
Figure 2. Soft-Start Application
© 2000 IMP, Inc.
USB High-Side Power Switches
5
A1PROS [ A1 PROS CO., LTD. ]
