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AP1212
(Rev.:2010)

DUAL USB HIGH-SIDE POWER SWITCH

Diodes Incorporated. 

NOT RECOMMENDED FOR

NEW DESIGN PLEASE USE

AP2146 OR AP2156

AP1212

DUAL USB HIGH-SIDE POWER SWITCH

Functional Description

Error Flag

An open-drained output of N-channel MOSFET, the FLG output

is pulled low to signal the following fault conditions: input under

voltage, output current limit, and thermal shutdown.

Current Limit

The current limit threshold is preset internally. It protects the

output MOSFET switches from damage due to undesirable short

circuit conditions or excess inrush current often encountered

during hot plug-in. The low limit of the current limit threshold of

the AP1212 allows a minimum current of 0.5A through the

MOSFET switches. A current limit condition will signal the error

flag.

Thermal Shutdown

When the chip temperature exceeds 140ºC for any reason other

than over current fault of either one of the two MOSFET switches,

the thermal shutdown function turns off both MOSFET switches

and signals the error flag. A hysteresis of 10ºC prevents the

MOSFETs from turning back on until the chip temperature drops

to below 130ºC.

Enable

Before EN is asserted, a delay of 10ms minimum from when the

supply voltage, Vcc, becomes stable must be allowed.

Supply Filtering

A 0.1µF to 1µF bypass capacitor from IN to GND, located near

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.

Transient Droop Requirements

USB applications support dynamic attachment (hot plug-in) of

peripherals. A current surge is caused by the input capacitance of

downstream device. Ferrite beads are recommended in series

with all power and ground connector pins. Ferrite beads reduce

EMI and limit the inrush current during hot-attachment by filtering

high-frequency signals.

Short Circuit Transient

Bulk capacitance provides the short-term transient current

needed during a hot-attachment event. With a 33µF,

16V tantalum or 100µF, 10V electrolytic capacitor mounted close

to downstream connector per port should provide transient drop

protection.

Printed Circuit Layout

The power circuitry of USB printed circuit boards requires a

customized layout to maximize thermal dissipation and to

minimize voltage drop and EMI.

AP1212 Rev. 8

DS31019

10 of 12

www.diodes.com

NOVEMBER 2010

© Diodes Incorporated

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