SP2526 datasheet(7/18 Pages) SIPEX

7 / 18 page

Rev. 8/21/01

SP2526 +3.0V to +5.5V USB Power Control Switch

minimum current of 0.5A to be delivered.

The SP2526 MOSFET switches will exhibit

very low resistance (<100m

Ω) or voltage drop

until the current limit is reached. The fold back

current is the current that is delivered into a short

circuit at the output.

If the SP2526 MOSFET switch is enabled into a

heavy load or short-circuit, the switch will im-

mediately go into a constant-current mode, re-

ducing the output voltage. The respective fault

flag will pull low until the condition is removed.

When a heavy load is connected to the SP2526

switch output, a large transient current may flow

until the current limiting circuitry responds.

The SP2526 will provide a low resistance switch

(100m

Ω) between the input and output pins.

This low resistance will be maintained with

increasing current until the 2.2A limit is reached.

If load current exceeds this limit, the switch will

increase its resistance. The foldback current

(500mA minimum) is reached when there is a

short applied to the output. The 100m

Ω switch

resistance is guaranteed for all load currents,

increasing or decreasing, that are below 500mA.

Thermal Shutdown

Under nominal load conditions, the switch resis-

tance is very low and internal power dissipation

is low. Under short circuit conditions, current is

limited and internal power dissipation is higher

but not extreme. Under intermediate load condi-

tions, both the voltage across the switch and the

current through the switch are at intermediate

values and internal power dissipation is highest.

In this last condition, the die temperature will

reach the thermal limit and the switches in both

channels will be shut off. As the die subse-

quently cools, the switch will turn on again. If

the load is not removed, the device will thermal

cycle in this manner to protect itself from dam-

age.

Thermal shutdown is asserted if the die tempera-

ture exceeds 135OC and will not release until the

die termperature drops below 125OC. Thermal

shutdown will disable both output MOSFET

switches and force both FLGA and FLGB fault

flags low.

The delay between a current limit fault and

thermal shutdown will vary with ambient tem-

perature, board layout, and load impedance, but

is typically several hundred milliseconds. A

designer

can command a USB controller to recognize the

fault and disable the appropriate channel within

this time.

TYPICAL APPLICATIONS

Bypass Capacitors

A 0.1

µF to 1.0µF bypass capacitor from the IN

pin to the GND pin is recommended to control

power supply transients. Refer to Figure 4.

Without a bypass capacitor, an output short may

cause sufficient ringing and damage the device.

Without a bypass capacitor, excessive supply

lead inductance is also a concern.

Input or output transients must not exceed the

absolute maximum supply voltage of V

IN(MAX) =

+6.0V even for a short duration to avoid risk of

damage to the device.

Transient Overcurrent Filter

When the SP2526 is enabled, large values 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 for FLGA and/or FLGB. The

duration of this time will depend on the size of

the output capacitance. During the capacitance

charging time, the device enters into foldback

mode. As the capacitance is charged, the current

decreases below the current-limit threshold and

the fault flags that are present at the FLGA and/

or FLGB pins will then be deasserted.

In USB applications, it is required that output

bulk capacitance is utilized to support hot-plug

occurences. When the SP2526 is enabled, the

flag may go active for about 1ms due to inrush

current exceeding the current-limit setpoint.

Additionally, during hot-plug events, inrush cur-

rents may also cause the fault flags at the FLGA

and/or FLGB pins to go active. Since these

conditions are not valid overcurrent faults, the

USB controller must ignore the fault flags during

these events. To prevent this, a 1ms RC filter can

be implemented as shown in Figure 5. Alterna-

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