Description of Operation
The FPF2148 is a current limited switch that protects systems
and loads which can be damaged or disrupted by the
application of high currents. The core of each device is a 0.12Ω
P-channel MOSFET and a controller capable of functioning over
a wide input operating range of 1.8-5.5V. The controller protects
against system malfunctions through current limiting,
undervoltage lockout and thermal shutdown and power good
features. The current limit is preset for 200mA.
The ONB pin controls the state of the switch. Activating ONB
continuously (ONB pin low) holds the switch in the on state so
long as there is no undervoltage on VIN or a junction
temperature in excess of 140°C. ONB is active LO and has a
low threshold making it capable of interfacing with low voltage
signals. In addition, excessive currents will cause the switch to
turn off due to thermal shutdown. The FPF2148 does not turn
off in response to a over current condition but instead remain
operating in a constant current mode so long as ONB is active
and the thermal shutdown or undervoltage lockout have not
The ON pin control voltage and VIN pin have independent
recommended operating ranges. The ON pin voltage can be
driven by a voltage level higher than the input voltage.
Upon the detection of an over-current, an input undervoltage, or
an over-temperature condition, the FLAGB signals the fault
mode by activating LO. And the FLAGB goes LO immediately. It
will remain LO during the faults and immediately returns HI at
the end of the fault condition. FLAGB is an open-drain output
which requires a pull-up resistor between VIN and FLAGB.
During shutdown, the pull-down on FLAGB is disabled to reduce
current draw from the supply.
The current limit ensures that the current through the switch
doesn't exceed 400mA while not limiting at less than 200mA.
The FPF2148 have no current limit blanking period so
immediately upon a current limit condition FLAGB is activated.
The part will remain in a constant current state until the ONB pin
is deactivated or the thermal shutdown turns-off the switch.
The thermal shutdown protects the die from internally or
externally generated excessive temperatures. During an over-
temperature condition the FLAGB is activated and the switch is
turned-off. The switch automatically turns-on again if
temperature of the die drops below the threshold temperature.
FPF2148 has a "Power Good" feature. PGOOD pin is an
open-drain MOSFET which asserts high when the output
voltage reaches 90% of the input voltage.
PGOOD pin requires an external pull up resistor that is con-
nected to the output voltage when there is no battery in the load
side and the logic level of the subsequent controller permits.
This would give logic levels similar to a CMOS output stage for
PGOOD, while still keeping the option to tie the pull-up to a dif-
ferent supply voltage. A 100KΩ is recommended to be used as
pull up resistor. The PGOOD pin status is independent of the
ONB pin position. This mean that PGOOD pin stays low when
the load switch is OFF. If the Power Good feature is not used in
the application the pin can be connected directly to GND.
Delay On Time
VOUT Rise Time
Turn On Time
Delay Off Time
VOUT Fall Time
Turn Off Time
The undervoltage lockout turns-off the switch if the input voltage
drops below the undervoltage lockout threshold. With the ONB
pin active the input voltage rising above the undervoltage
lockout threshold will cause a controlled turn-on of the switch
which limits current over-shoots.
FPF2148 Rev. H