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Date: 12/22/04 SP2525A USB High-Side Power Switch © Copyright 2004 Sipex Corporation
Error Flag
An error Flag is an open-drained output of an 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 resulting from undesirable short circuit
conditions or excess inrush current, which is
often encountered during hot plug-in. The low
limit of the current limit threshold of the
SP2525A allows a minimum current of 0.5A
through the MOSFET switches. A current limit
condition will signal the error flag.
Thermal Shutdown
When temperature of SP2525A exceeds 135ºC
for any reasons, the thermal shutdown function
turns off the MOSFET switch and signals the
error flag. A hysteresis of 10ºC prevents the
MOSFETs from turning back on until the chip
temperature drops below 125ºC.
Supply Filtering
A 0.1µF to 1µF bypass capacitor from IN to
GND, located near the device, is strongly rec-
ommended to control supply transients. With-
out a bypass capacitor, an output short may
cause sufficient ringing on the input (from
supply lead inductance) to damage internal
control circuitry.
APPLICATION INFORMATION
Transient Requirements
USB supports 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 tran-
sient current needed during a hot-attachment event.
A 33 µF/16V tantalum or a 100µF/10V electro-
lytic capacitor mounted close to downstream con-
nector each port should provide transient drop
protection
Printed Circuit Layout
The Power circuitry of USB printed circuit boards
requires a customized layout to maximize ther-
mal dissipation and to minimize voltage drop and
EMI.