SP2525 Datasheet, PDF (7/16 Pages) Sipex Corporation – +3.0V to +5.5V USB Power Control Switch

Output Current Limiting
The switch control circuit will implement cur-
rent limiting which prevents damage to the
device and the external load while allowing a
minimum current of 0.5A.
The SP2525 MOSFET switches will exhibit
very low resistance (≤ 100mΩ) or voltage drop
until the current limit is reached. As the load
resistance decreases further, the current sup-
plied will decrease until it reaches the foldback
current, 500mA minimum. The foldback cur-
rent is the current that is delivered into a short
circuit at the output.
If a MOSFET switch is enabled into a heavy
load or short-circuit, the switch will immedi-
ately go into a constant-current mode, reducing
the output voltage. The fault flag is forced low
until the excessive load is removed.
Thermal Shutdown
Thermal shutdown is asserted if the die tem-
perature exceeds 135^OC and will not release
until the die temperature drops below 125^OC.
Thermal shutdown will disable the output
MOSFET switch and force fault flag low.
The delay between flag assertion and thermal
shutdown can vary with ambient temperature,
board layout, and load impedance, but is typi-
cally several hundred milliseconds. The USB
controller, recognizing a fault, can disable the
device within this time, otherwise the device
will thermal cycle. This does not cause damage
to the SP2525.
TYPICAL APPLICATIONS
Bypass Capacitors
Recommended is a 0.1µF to 1.0µF bypass ca-
pacitor from the IN pin to the GND pin to control
power supply transients. Without a bypass
capacitor, an output short may cause sufficient
ringing to damage the internal circuitry.
Input or output transients must not exceed the
absolute maximum supply voltage even for a
short duration without risk of damage to the
device. V_IN(MAX) = +6.0V.
Soft Start Condition
The soft start feature of the SP2525 device is
implemented by holding the output turn on rise
time to 1ms. When off, the device has high
impedance MOSFET channels that slowly be-
come low impedance as the device powers on.
This prevents an inrush current from causing
voltage drops that result from charging a capaci-
tive load. This satisfies the USB voltage droop
requirements for bus-powered applications.
Enable Input
The EN control pin must be driven to a logic
high or logic low for a clearly defined signal
input. Floating this control line may cause
unpredictable operation.
Transient Overcurrent Filter
When the SP2525 device is enabled, large val-
ues of capacitance at the output of the device
will cause inrush current to exceed the short
circuit current-limit threshold of the device and
assert a flag fault condition. The duration of this
time will depend on the size of the output ca-
pacitance. During the capacitance charging
time, the device enters constant-current mode.
As the capacitance is charged, the current de-
creases below the short circuit current-limit
threshold and the fault flags will be de-asserted.
In USB applications, it is required that output
bulk capacitance is utilized to support hot-plug
occurrences. When the SP2525 device is en-
abled, the flag may go active for about 1ms due
to inrush current exceeding the current-limit.
Additionally, during hot-plug events, inrush cur-
rents may also cause the fault flag to go active
for 1ms. Since these conditions are not valid
overcurrent faults, the USB controller must ig-
nore the fault flags during these events. To
prevent this, a 1ms RC filter maybe useful as
shown in Figure. Alternatively, a 1ms debounce
routine may be programmed into the USB logic
controller, eliminating the need for the RC filter.
Rev. 8/21/01
SP2525 +3.0 to +5.5 Power Control Switch
7
© Copyright 2001 Sipex Corporation