AP1212

DUAL USB HIGH-SIDE POWER SWITCH

AP1212 Rev. 2

10 of 12

FEBRUARY 2007

www.diodes.com

Function Description

Error Flag

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

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

undervoltage, 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.

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.