SP2525A Datasheet, PDF (4/9 Pages) Sipex Corporation – USB High-Side Power Switch

APPLICATION INFORMATION
Error Flag
The Error Flag is an open-drained output of
an N-channel MOSFET, the FLG output is
pulled low to signal the following fault con-
ditions: input undervoltage, output current
limit, and thermal shutdown.
Current Limit
The current limit threshold is preset inter-
nally. It protects the output MOSFET
switches from damage resulting from un-
desirable 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 al-
lows a minimum current of 0.5A through the
MOSFET switches. A current limit condi-
tion will signal the Error Flag.
Thermal Shutdown
When the temperature of the SP2525A
exceeds 135ºC for any reasons, the ther-
mal 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 tempera-
ture drops below 125ºC.
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 ringing on the input (from sup-
ply lead inductance) which can damage
internal control circuitry.
Transient Requirements
USB supports dynamic attachment (hot plug-
in) of peripherals. A current surge is caused
by the input capacitance of a 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 fil-
tering high-frequency signals.
Short Circuit Transient
Bulk capacitance provides the short-term
transient current needed during a hot-attach-
ment event. A 33 µF/16V tantalum or a 100µF/
10V electrolytic capacitor mounted close to
the downstream connector at each port should
provide sufficient transient drop protection.
Printed Circuit Layout
The Power circuitry of USB printed circuit
boards requires a customized layout to maxi-
mize thermal dissipation and to minimize
voltage drop and EMI.
Input and Output
The independent solid state switch connects
the IN pin to the OUT pin when enabled by a
logic signal at EN. The IN pin is the power
supply connection to the internal circuitry and
the drain of the output MOSFET. The OUT
pin is the source for the MOSFET. Typically,
the current in USB application will flow through
the switch from IN to OUT towards the load.
If VOUT is greater than VIN when a switch is
enabled, the current will flow from OUT to the
IN pin because the MOSFET channels are
bidirectional when switched on. The output
source is allowed to be externally forced to a
higher voltage than its input without causing
unwanted current flow when the output is
disabled.
Date: 5/3/06 Rev I
SP2525A USB High-Side Power Switch
4
© Copyright 2006 Sipex Corporation