7

Rev. 8/21/01

SP2525 +3.0 to +5.5 Power Control Switch

© Copyright 2001 Sipex Corporation

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-

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 0.1

µF 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

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.