ap1212 Diodes, Inc., ap1212 Datasheet - Page 10

• Manufacturer Part Number: ap1212
• Description: Usb Power Switch Dual Usb High-side Power Switch
• Manufacturer: Diodes, Inc.

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.
AP1212 Rev. 4
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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.
DUAL USB HIGH-SIDE POWER SWITCH
©
AP1212
Diodes Incorporated
APRIL 2008