ACE345E

Adjustable USB Load Current Switch

VER 1.2

9

Application Information

Input Output Capacitance

Input and output capacitance improves the performance of the device; the actual capacitance should be

optimized for the particular application. For all applications, a 4.7µF or greater ceramic bypass capacitor

between IN and GND is recommended as close to the device as possible for local noise de-coupling. This

precaution reduces ringing on the input due to power-supply transients. Additional input capacitance may

be needed on the input to reduce voltage overshoot from exceeding the absolute maximum voltage of the

device during heavy transient conditions. This is especially important during bench testing when long,

inductive cables are used to connect the evaluation board to the bench power-supply. Placing a

high-value electrolytic capacitor on the output pin is recommended when large transient currents are

expected on the output.

Setting The Current Limit Threshold

Ω)

Typical Current Limit (mA)

Ω)

Typical Current Limit (mA)

200

138

51

520

180

152

43

612

151

179

30

873

100

266

20

1295

82

324

15.1

1705

68

389

Power Dissipation

During normal operation as a switch, the power dissipated in the part will depend upon the level at which

the current limit is set. The maximum allowed setting for the current limit is 1A and this will result in a

power dissipation of,

P = (ILIM)

If the part goes into current limit the maximum power dissipation will occur when the output is shorted to

ground. This is more power than the package can dissipate, but the thermal shutdown of the part will

activate to protect the part from damage due to excessive heating. A short on the output will cause the

part to operate in a constant current state dissipating a worst case power of,

P(max) = VIN(max) x ILIM(max) = 5.5 x 1 = 5W

This large amount of power will activate the thermal shutdown and the part will cycle in and out of thermal

shutdown so long as the ON pin is active and the short is present.