Description of Operation
FPF2024-FPF2027 series Full-Function switches are
current limited load switches with ultra-low power
consumption. The core of each device consists of a
230 mW P-channel MOSFET featuring slow turn-on to
limit the inrush current, fast turn-off, current limit, Under-
Voltage Lockout (UVLO) and thermal shutdown
protection features and a FLAGB output that indicates
that a fault condition has occurred.
Some versions in the FPF202x series also feature
Current Limit Blanking and Auto-Restart.
The FPF202x family achieves an ultra-low current
consumption of 1 μA through a proprietary “Sleep and
Wake-up Modes” implementation. Full functionality is
guaranteed for operating voltages down to 1.6 V over
the -40°C to +85°C temperature range.
Sleep and Wakeup Mode Description
The ultra-low power consumption of FPF2024-FPF2027
is achieved through the implementation of proprietary
Sleep/ Wakeup modes.
The FPF2024-FPF2027 family turns on in Startup mode
where it checks for potential load current, temperature,
and under-voltage faults for 10 ms. If no faults are
detected during this startup period, the FPF2024-
FPF2027 goes into a Sleep mode where it stays for
257 ms. At the end of the Sleep period, the part goes
into Wakeup mode to check for any fault condition. If no
fault is detected in 1 ms, the part goes back to Sleep
mode. The 1:257 Wakeup/Sleep duty cycle results in an
overall average current consumption of 1 μA (typical).
During Sleep mode the thermal and under-voltage
conditions are not monitored to reduce the current
consumption of the device.
The switch current limiting circuitry is active at all times
and protects the FPF2024-FPF2027 against excessive
load currents in all modes. While in the Wakeup mode,
a current fault event will prevent the part from re-
entering into Sleep mode even if input voltage and
temperature faults are not present. In such a case, the
part functions according to its feature set, e.g., it
performs its normal Blanking, Auto-Restart or Latch-off
functions as expected. If the over-current condition is
removed from the output, the part will go back into
Sleep mode after 10ms. The representative state
diagrams of the FPF2024-FPF2027 are given in Figure
25, Figure 26 and Figure 27.
The ultra-low quiescent current consumption of 1 μA
along with the very-low minimum operating voltage of
1.6 V, make the FPF2024-FPF2027 an ideal full-
function load switch for ultraportable applications.
The ON pin controls the state of the switch. The
FPF2024- FPF2027 series features both active high and
low configurations to accommodate various application
requirements. FPF2024, FPF2026 and FPF2027 are
active high switches while the FPF2025 is an active low
device. Applying a continuous high or low signal
depending on the switch configuration, will hold the
switch in the ON state. The load switch will move into
the OFF state when the ON pin is inactive. In addition,
FPF2026 moves into the OFF state if a current fault is
encountered for longer duration than the Blanking Time.
For all versions, an under-voltage on VIN or a junction
temperature in excess of 140°C overrides the ON
control and turns off the switch.
In addition, a current fault condition longer than the
Blanking Time will cause the switch to turn off in the
FPF2024, FPF2025 and FPF2026. The FPF2024 and
FPF2025 have an Auto-Restart feature which will
automatically turn the switch on again after 70 ms. For
the FPF2026, the ON pin must be toggled to turn the
switch on again. The FPF2027 does not turn off in
response to an over-current condition, and remains in a
constant current mode for so long as the ON pin is
active, and the thermal shutdown or UVLO are 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.
Over-current, input under-voltage, or over-temperature
fault conditions are signaled out by the FLAGB pin going
low. FPF2024, FPF2025 and FPF2026 have a current
fault blanking feature which prevents current faults
lasting shorter than the Blanking Time of 10 ms (typical)
from triggering the fault signal (FLAGB) output.
If the over-current condition persists beyond the
Blanking Time, the FPF2024 and FPF2025 pull the
FLAGB pin low and shut the switch off. If the ON pin is
kept active, an Auto-Restart feature releases the
FLAGB pin and turns the switch on again after 70 ms.
If the over-current condition persists beyond the
Blanking Time, the FPF2026 has a Latch-Off feature
which pulls the FLAGB pin low and shuts the switch off.
The switch is kept off and the FLAGB pin is kept low
until the ON pin is toggled.
The FPF2027 responds to an overload condition by
immediately pulling the FLAGB pin low and the switch
remains in constant current mode until the output
overload condition is removed. The FPF2027 has a
Startup Blanking feature which prevents current faults
related to startup transients from triggering the FLAGB
output. The Startup Blanking feature is effective for the
first 10 ms (typical) following device turn-on via ON pin.
The FPF2024, FPF2026 and FPF2027 have an open-
drain MOSFET FLAGB output which requires a pull-up
resistor between VIN and FLAGB. A 100 KΩ pull up
resistor is recommended. The FPF2025 has a CMOS
FLAGB output and does not require a pull-up resistor.
During shutdown, the pull-down on FLAGB is disabled
to reduce current draw from the supply.
© 2008 Fairchild Semiconductor Corporation
FPF2024/25/26/27 • Rev. 1.1