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)
R
ILIM
(K)
200
138
180
152
151
179
100
266
82
324
68
389
51
520
43
612
30
873
20
1295
15.1
1705
Current Limit Threshold VS RILIM
1800
1600
1400
1200
1000
800
600
400
Current Limit Threshold(mA)
Ilim
200
0
0
50
100
150
Rset(Kohm)
200
250
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,
2
2
P = (ILIM) x RDS = (1) x 0.10 = 100mW
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
.
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