FPF2195 데이터 시트보기 (PDF) - Fairchild Semiconductor
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FPF2195 Datasheet PDF : 14 Pages
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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 mΩ P-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 to 1.5 A through the
selection of an external resistor.
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.
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
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.
where:
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. 1.0.5
10
www.fairchildsemi.com
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