IMP2526
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 pins, ENA/ENB, must be
itor to control transients on the power supply pin. This capacitor, driven to a definitive logic state at all times. Floating the input
connected from IN to GND, should be in close proximity to the can result in spurious operation. Do not drive ENA/ENB
IMP2526 for maximum transient suppression. The lack of suitable below GND.
bypassing can result in ringing on the IN input when transients
Fault Flag Output
Soft Start
The IMP2526 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-
occur. This ringing, due to supply lead inductance, could damage
IMP2526 control circuitry if the 8V maximum input rating is
exceeded.
2.7V 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 IMP2526 provides
this high-load, soft-start operation.
IMP2526
7
IN
6
GND
0.1µF to 1µF
2526_04.eps
Figure 1. Supply Bypassing
USB
Controller
IMP2526-xBM
8
7
6
1
2
3
VBUS
ENA
OUTA
IN
FLGA
FLGB
ENB
0.1µF
Capacitive
Load
GND
OUTB
USB
Host
4
5
4.7µF
CBULK
GND
Cable
Bus Powered Hub
Cable
Downstream USB Device
2526_06.eps
Figure 2. Soft-Start Application
© 2000 IMP, Inc.
USB High-Side Power Switches
5
A1PROS [ A1 PROS CO., LTD. ]
