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FPF2194 Datasheet

Full-Function Load Switch

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Functional Description
The FPF2193, FPF2194, and FPF2195 are current-
limited switches that protect systems and loads that can
be damaged or disrupted by the application of high
currents. The core of each device is a 55 mP-channel
MOSFET and a controller capable of functioning over the
wide input operating range of 1.8- 5.5 V. The controller
protects against system malfunctions through current
limiting, under-voltage lockout, and thermal shutdown.
The current limit is adjustable from 100 mA (45 mA for
FPF2195BUCX) to 1.5 A through the selection of an
external resistor.
On/Off Control
The ON pin controls the state of the switch. When ON is
HIGH, the switch is in 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 cause the switch to turn off in the
FPF2193 and FPF2194. The FPF2193 has an auto-
restart feature that automatically turns the switch on again
after 450 ms. For the FPF2194, the ON pin must be
toggled to turn the switch on again. The FPF2195 does
not turn off in response to an over-current condition, but
remains operating in constant-current mode as long as
ON is active and the thermal shutdown or under-voltage
lockout have not activated.
Fault Reporting
Upon the detection of an over-current, input under-
voltage, or over-temperature condition, FLAGB signals
the fault mode by activating LOW. For the FPF2193 and
FPF2194, the FLAGB goes LOW at the end of the
blanking time, while FLAGB goes LOW immediately for
the FPF2195. FLAGB remains LOW through the auto-
restart time for the FPF2195. For the FPF2194, FLAGB is
latched LOW and ON must be toggled to release it. With
the FPF2195, FLAGB is LOW during the faults and
immediately returns HIGH at the end of the fault
condition. FLAGB is an open-drain MOSFET that 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.
Current Limiting
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 limit is adjustable through the selection of
an external resistor connected to ISET. Information for
selecting the resistor is found in the Application
Information section. The FPF2193 and FPF2194 have a
blanking time of 30 ms, nominally, during which the
switch acts as a constant current source. At the end of
the blanking time, the switch is turned off. The FPF2195
has no current limit blanking period, so it remains 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,
the short-circuit detection threshold voltage, the current
limit value is re-conditioned and the 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 5.5 V input
voltage. The VSCTH value is set to be 1 V. At around 1.1 V
of output voltage, the switch is removed from short-circuit
current-limiting mode and the current limit is set to the
current limit value.
Under-Voltage Lockout (UVLO)
The under-voltage lockout turns the switch off 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 causes a controlled turn-
on of the switch, which limits current over shoot.
Thermal Shutdown
The thermal shutdown protects the die from internally or
externally generated excessive temperatures. During an
over-temperature condition, 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.
Reverse-Current Blocking
The entire FPF2193/94/95 family has a reverse current
blocking feature that protects the input source against
current flow from output to input. For a standard USB
power design, this is an important feature to protect the
USB host from being damaged due to reverse current
flow on VBUS.
When the load switch is OFF, no current flows from the
output to the input. If the switch is turned on and the
output voltage is greater than input voltage, this feature is
activated and turns off the switch. This prevents any
current flow from output to input. The reverse-current
blocking feature is deactivated if the VOUT - VIN is smaller
than a typically 50 mV threshold. During this time, some
current (50 mV/RON) flows from the output to input until
input voltage becomes greater than output voltage.
FLAGB operation is independent of the reverse-current
blocking and does not report a fault condition if this
feature is activated.
Figure 27.
tdON = Delay On Time
tR = VOUT Rise Time
tON = Turn-On Time
tdOFF = Delay Off Time
tF = VOUT Fall Time
tOFF = Turn-Off Time
Timing Diagram
© 2009 Fairchild Semiconductor Corporation
FPF2193/4/5 • Rev. 1.0.9
Fairchild Semiconductor
Fairchild Semiconductor

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