MIC2025(2000) 查看數據表（PDF） - Micrel

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MIC2025
(Rev.:2000)

Single-Channel Power Distribution Switch

Micrel 

MIC2025/2075

Applications Information

Supply Filtering

A 0.1µF to 1µF bypass capacitor positioned close to VIN and

GND of the device is strongly recommended to control supply

transients. Without a bypass capacitor, an output short may

cause sufficient ringing on the input (from supply lead induc-

tance) to damage internal control circuitry.

Printed Circuit Board Hot-Plug

The MIC2025/75 are ideal inrush current-limiters suitable for

hot-plug applications. Due to the integrated charge pump,

the MIC2025/75 presents a high impedance when off and

slowly becomes a low impedance as it turns on. This “soft-

start” feature effectively isolates power supplies from highly

capacitive loads by reducing inrush current during hot-plug

events. Figure 3 shows how the MIC2075 may be used in a

hot-plug application.

In cases of extremely large capacitive loads (>400µF), the

length of the transient due to inrush current may exceed the

delay provided by the integrated filter. Since this inrush

current exceeds the current-limit delay specification, FLG will

be asserted during this time. To prevent the logic controller

from responding to FLG being asserted, an external RC filter,

as shown in Figure 4, can be used to filter out transient FLG

assertion. The value of the RC time constant will be selected

to match the length of the transient.

Micrel

Universal Serial Bus (USB) Power Distribution

The MIC2025/75 is ideally suited for USB (Universal Serial

Bus) power distribution applications. The USB specification

defines power distribution for USB host systems such as PCs

and USB hubs. Hubs can either be self-powered or bus-

powered (that is, powered from the bus). Figure 5 below

shows a typical USB Host application that may be suited for

mobile PC applications employing USB. The requirements

for USB host systems is that the port must supply a minimum

of 500mA at an output voltage of 5V ±5%. In addition, the

output power delivered must be limited to below 25VA. Upon

an overcurrent condition, the host must also be notified. To

support hot-plug events, the hub must have a minimum of

120µF of bulk capacitance, preferably low-ESR electrolytic or

tantulum. Refer to Application Note 17 for more details on

designing compliant USB hub and host systems.

For bus-powered hubs, USB requires that each downstream

port be switched on or off under control by the host. Up to four

downstream ports each capable of supplying 100mA at 4.4V

minimum are allowed. In addition, to reduce voltage droop on

the upstream VBUS, soft-start is necessary. Although the hub

can consume up to 500mA from the upstream bus the hub

must consume only 100mA max at start-up, until it enumer-

ates with the host prior to requesting more power. The same

requirements apply for bus-powered peripherals that have no

downstream ports. Figure 6 shows a bus-powered hub.

March 2000

VCC

to "Hot"

Receptacle

GND

MIC2025-2

1 EN

OUT 8

0.1 2 FLG

µF 3 GND

IN 7

OUT 6

4 NC

NC 5

Backend

Function

CBULK

Adaptor Card

Figure 3. Hot Plug Application

Logic Controller

OVERCURRENT

V+

10k

R

C

MIC2025

1 EN

OUT 8

2 FLG

IN 7

3 GND OUT 6

4 NC

NC 5

Figure 4. Transient Filter

11

MIC2025/2075

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