MIC2525 Datasheet, PDF (9/12 Pages) Micrel Semiconductor – USB Power Control Switch Not Recommended for New Designs

MIC2525
Applications Information
Supply Filtering
A 0.1µF to 1µF bypass capacitor from IN to GND, located at
the device, is strongly recommended to control supply tran-
sients. Without a bypass capacitor, an output short may
cause sufficient ringing on the input (from supply lead induc-
tance) to damage internal control circuitry.
Input or output transients must not exceed the absolute
maximum supply voltage (V_{IN max} = 6V) even for a short
duration.
3V to 5.5V
MIC2525
1 _EN
OUT ⁸
2 _FLG
IN ⁷
3 _{GND OUT} 6
4 _NC
NC ⁵
0.1µF to 1µF
Figure 1. Supply Bypassing
Micrel
Enable Input
EN must be driven logic high or logic low for a clearly defined
input. Floating the input may cause unpredictable operation.
EN should not be allowed to go negative with respect to GND.
Soft Start
The MIC2525 presents a high impedance when off, and
slowly becomes a low impedance as it turns on. This reduces
inrush current and related voltage drop that results from
charging a capacitive load, satisfying the USB voltage droop
requirements for bus-powered applications as shown in
Figure 2.
The soft start circuit shown in Figure 3 can be utilized to meet
USB transient regulation specifications with large load ca-
pacitances (C_BULK > 10uF). The MIC2525 will provide inrush
current limiting for these applications.
Transient Overcurrent Filter
When the MIC2525 is enabled, large values of capacitance
at the output of the device will cause inrush current to exceed
the short circuit current-limit threshold of the device and
assert the flag. The duration of this time will depend on the
size of the output capacitance. Refer to the “Functional
Characteristics” turn-on and turnoff behaviors for details.
V_BUS
USB Host
GND
Cable
MIC2525-xBM
1 _EN
OUT ⁸
2 _FLG
IN ⁷
3 _GND
4.7
µF ⁴ _NC
OUT ⁶
NC ⁵
USB
Controller
0.1µF
C_BULK
Bus Powered Hub
Cable
Figure 2. Soft-Start Application
Capacitive
Load
Downstream USB Device
V_BUS
USB Hub
GND
Cable
MIC2525-2
1 _EN
OUT ⁸
4.7 ^{2 FLG}
µF _{3 GND}
IN ⁷
OUT ⁶
4 _NC
NC ⁵
USB Peripheral
USB
Controller
USB
Function
C_BULK
Figure 3. Inrush Current-Limit Application
January 2000
9
MIC2525