MIC2074 datasheet(13/16 Pages) MICREL

13 / 16 page

Micrel, Inc.

MIC2073/2074

January 2009

M9999-011209

VEN

VOUT

IOUT

Short-Circuit Fault

Thermal

Shutdown

Reached

Load and Fault Removed

(Output Reset)

VFLG

ILIMIT

ILOAD

3ms typ.

delay

Figure 2. MIC2073-2 Fault Timing

Application 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 inductance) to damage internal control

circuitry.

Printed Circuit Board Hot-Plug

The MIC2073/2074 are ideal inrush current-limiters for

hot plug applications. Due to their integrated charge

pumps, the MIC2073/2074 present a high impedance

when off and slowly becomes a low impedance as their

integrated charge pumps turn on. This “soft-start” feature

effectively isolates power supplies from highly capacitive

loads by reducing inrush current. Figure 3 shows how

the MIC2074 may be used in a card 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 should be selected to

match the length of the transient, less tD(min) of the

MIC2073/2074.

Universal Serial Bus (USB) Power Distribution

The MIC2073/2074 are 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 shows a typical USB Host application

that may be suited for mobile PC applications employing

USB. The requirement 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 tantalum. Please 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

enumerates 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.

MIC2074 Datasheet(PDF) 13 Page - Micrel Semiconductor

MIC2074 Datasheet(HTML) 13 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL