February 2000

9

MIC2526

MIC2526

Micrel

Applications Information

Supply Filtering

A 0.1

µF 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

duration.

MIC2526

ENA

OUTA

FLGA

FLGB

GND

ENB

OUTB

IN

0.1µF to 1µF

3.0V to 5.5V

Figure 1. Supply Bypassing

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 MIC2526 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

current limiting for these applications.

Transient Overcurrent Filter

When the MIC2526 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.

During the capacitance charging time, the device enters into

constant-current mode. As the capacitance is charged, the

current decreases below the short circuit current-limit thresh-

old, and the flag will then be deasserted.

MIC2526-xBM

ENA

OUTA

FLGA

FLGB

GND

OUTB

IN

18

27

36

5

0.1µF

Capacitive

Load

USB

Controller

ENB

4

Bus Powered Hub

Downstream USB Device

Cable

Cable

USB Host

GND

4.7

µF

Figure 2. Soft Start (Single Channel)

MIC2526-2BM

ENA

OUTA

FLGA

FLGB

GND

OUTB

IN

18

27

36

5

USB

Controller

ENB

4

USB Peripheral

Cable

USB Hub

GND

4.7

µF

USB

Function

USB

Function

Figure 3. Inrush Current-Limit Application