Description of Operation
The FPF2163, FPF2164, and FPF2165 are current limited
switches that protect 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, under-voltage lockout and thermal
shutdown. The current limit is adjustable from 150mA to 1.5A
through the selection of an external resistor.
The ON pin controls the state of the switch. When ON is high,
the switch is in the on state. Activating ON continuously holds
the switch in the on state so long as there is no fault. For all
versions, an under-voltage on VIN or a junction temperature in
excess of 140°C overrides the ON control to turn off the switch.
In addition, excessive currents will cause the switch to turn off in
the FPF2163 and FPF2164. The FPF2163 has an Auto-Restart
feature which will automatically turn the switch on again after
450ms. For the FPF2164, the ON pin must be toggled to turn-on
the switch again. The FPF2165 does not turn off in response to
an over current condition but instead remains operating in a
constant current mode so long as ON is active and the thermal
shutdown or under-voltage lockout have not activated.
Upon the detection of an over-current, an input under-voltage,
or an over-temperature condition, the FLAGB signals the fault
mode by activating LO. For the FPF2163 and FPF2164, the
FLAGB goes LO at the end of the blanking time while FLAGB
goes LO immediately for the FPF2165. FLAGB remains LO
through the Auto-Restart Time for the FPF2165. For the
FPF2164, FLAGB is latched LO and ON must be toggled to
release it. With the FPF2165, FLAGB is LO during the faults and
immediately returns HI at the end of the fault condition. FLAGB
is an open-drain MOSFET 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 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 ISET. Information for selecting the resistor is found
in the Application Info section. The FPF2163 and FPF2164
have a blanking time of 30ms, nominally, during which the
switch will act as a constant current source. At the end of the
blanking time, the switch will be turned-off. The FPF2165 has
no current limit blanking period so it will remain in a constant
current state until the ON pin is deactivated or the thermal
shutdown turns-off the switch.
For preventing the switch from large power dissipation during
heavy load a short circuit detection feature is introduced. Short
circuit condition is detected by observing the output voltage.
The switch is put into short circuit current limiting mode if the
switch is loaded with a heavy load. When the output voltage
drops below VSCTH, short circuit detection threshold voltage,
the current limit value re-conditioned and short circuit current
limit value is decreased to 62.5% of the current limit value. This
keeps the power dissipation of the part below a certain limit
even at dead short conditions at 5.5V input voltage. The VSCTH
value is set to be 1V. At around 1.1V of output voltage the
switch is removed from short circuit current limiting mode and
the current limit is set to the current limit value.
The under-voltage lockout turns-off the switch if the input
voltage drops below the under-voltage lockout threshold. With
the ON pin active the input voltage rising above the under-
voltage lockout threshold will cause a controlled turn-on of the
switch which limits current over-shoots.
Reverse Current Blocking
The entire FPF2163/65 family has a Reverse Current Blocking
feature that protects input source against current flow from
output to input. For a standard USB power design, this is an
important feature which protects the USB host from being
damaged due to reverse current flow on VBUS. The reverse
current blocking feature is active when the load switch is turned
If ON pin is LO and output voltage become greater than input
voltage, no current can flow from the output to the input . The
FLAGB operation is independent of the Reverse Current
blocking feature and will not report a fault condition if this
feature is activated.
The thermal shutdown protects the die from internally or exter-
nally generated excessive temperatures. During an over-tem-
perature condition the FLAGB is activated and the switch is
turned-off. The switch automatically turns-on again if tempera-
ture of the die drops below the threshold temperature.
FPF2163/4/5 Rev. C3