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FPF2108-FPF2110 Rev. E

Description of Operation

The FPF2108-FPF2110 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 the device is a 0.125

Ω

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

preset for either 200mA or 400mA.

On/OffControl

The ON pin controls the state of the switch. Active HI and LO

versions are available. Refer to the Ordering Information for

details. Activating ON continuously holds the switch in the on

state so long as there is no fault.

For all versions, an

150°C overrides the ON control to turn off the switch. For

FPF2108, the ON pin must be toggled to turn on the switch

again. The FPF2109 and FPF2110 do not turn off in response

to a over current condition but instead remain operating in a

constant current mode so long as ON is active and the thermal

shutdown or under-voltage lockout have not activated. When

the MOSFET is off, the body diode is disabled so no current

can flow through it.

Fault Reporting

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 FPF2108, the FLAGB goes LO

at the end of the blanking time while FLAGB goes LO immedi-

ately for the FPF2109 and FPF2110. For the FPF2108, FLAGB

is latched LO and ON must be toggled to release it.With the

FPF2109 and FPF2110, 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

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. For the FPF2109 the minimum current is

200mA and the maximum current is 400mA and for the

FPF2108 and FPF2110 the minimum current is 400mA and the

maximum current is 800mA. The FPF2108 has a blanking time

of 10ms, 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 and the FLAGB pin will activate to

indicate that current limiting has occurred. The FPF2109 and

FPF2110 have no current limit blanking period so immediately

upon a current limit condition FLAGB is activated. These parts

will remain in a constant current state until the ON pin is

deactivated or the thermal shutdown turns-off the switch.

Under-Voltage Lockout

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.

Thermal Shutdown

The thermal shutdown protects the part 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 the

temperature of the die drops below the threshold temperature.