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4

BL2555

REVERSE-VOLTAGE BLOCKING

The reverse-voltage protection feature turns off the

Power MOSFET whenever the output voltage exceeds

the input voltage by 150mV (typ) for 4-ms (typ). This

prevents damage to devices on the input side of the

BL2555 by preventing significant current from sinking

into the input capacitance. The BL2555 allow the

power MOSFET to turn on once the output voltage

goes below the input voltage for the same 4-ms

deglitch time.

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

Typical Current Limit (mA)

200

138

180

152

151

179

100

266

82

324

68

389

51

520

43

612

30

873

20

1295

15.1

1705

THERMAL CONSIDERATIONS

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

.

0

200

400

600

800

1000

1200

1400

1600

1800

0

50

100

150

200

250

Rset(Kohm)

Current Limit Threshold VS RILIM

Ilim