BL2553
PIN DESCRIPTION
PIN #
NAME
DESCRIPTION
Current limit Output. Bypass with a capacitor that is greater than 120F if used for
USB
1
OUT
Current limit threshold setting pin. Connect a resistor from this pin to GND to set
different current limit values
2
3
ILIM
Fault flagging pin. Connect a pull up resistor to IN, when in fault conditions, this pin
is asserted low
nFAULT
4
5
6
EN
Enable pin
GND
IN
Ground
Power input. Bypass with a 4.7F capacitor to GND
FUNCTION DESCRIPTION
The BL2553 is a load switch which provides full
protection to systems and loads which may
encounter large current conditions. BL2553 offers
a 95mΩ current-limited switch which can operate
over an input voltage range of 2.5-5.5V. The
current limit can be externally programmed by a
precision resistor, ranges from 75mA to 1.7A.
BL2553 also features reverse voltage blocking,
UVLO, and thermal shutdown to protect IC from
overheating. An nFAULT flag output provides a
pull-down signal to indicate fault conditions.
the input side of the BL2553 by preventing
significant current from sinking into the input
capacitance. The BL2553 allow the power
MOSFET to turn on once the output voltage goes
below the input voltage for the same 4-ms
deglitch time. The reverse-voltage condition also
asserts the nFAULT output (active-low) after 4-ms.
During “OFF” condition, the reverse-voltage
blocking function is still in effect, preventing any
current floating from OUT to IN even when the
device is not in use.
CURRENT LIMITING
nFAULT FLAG
The current limit ensures that the current
through the switch doesn't exceed a maximum
value while not limiting at less than a minimum
value. The current at which the parts will limit is
adjustable through the selection of an external
resistor connected to ILIM. Information for
selecting the resistor is found in the Application
Info section. BL2553 thermal cycles if an overload
condition is present long enough to activate
thermal limiting in any of the above cases. The
device turns off when the junction temperature
exceeds 135°C (typ) while in current limit. The
device remains off until the junction temperature
cools 10°C (typ) and then restarts
The FAULT open-drain output is asserted (active
low) during an overcurrent, over temperature or
reverse-voltage condition. The BL2553 asserts the
FAULT signal until the fault condition is removed
and the device resumes normal operation. The
nFAULT signal is de-asserted once device power is
cycled or the enable is toggled and the device
resumes normal operation. The BL2553 and
BL2553is designed to eliminate false nFAULT
reporting by using an internal delay "deglitch"
circuit for overcurrent (9-ms typ) and
reverse-voltage (4.5-ms typ) conditions without
the need for external circuitry. This ensures that
nFAULT is not accidentally asserted due to
normal operation such as starting into a heavy
capacitive load. The deglitching circuitry delays
entering and leaving fault conditions. Over
temperature conditions are not deglitched and
assert the nFAULT signal immediately.
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
3