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FPF2140/42/43/44/46/47 Rev. D

Description of Operation

The FPF2140/42/43/44/46/47 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, undervoltage lockout and thermal shutdown. The

current limit is preset for either 200mA or 400mA.

On/Off Control

The ON pin controls the state of the switch. Activating ON

continuously holds the switch in the on state so long as there is

140°C. ON is active HI and has a low threshold making it

capable of interfacing with low voltage signals. In addition,

excessive currents will cause the switch to turn off for FPF2140/

42 and FPF2144/46. The FPF2140/44 have an

Auto-Restart

feature which will automatically turn the switch on again after

450ms. For the FPF2142/46, the ON pin must be toggled to

turn-on the switch again. With no auto-restart, the FPF2143/47

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 undervoltage lockout

have not activated.

Fault Reporting

Upon the detection of an over-current, an input undervoltage, or

an over-temperature condition, the FLAGB signals the fault

mode by activating LO. For the FPF2140/42/44/46, the FLAGB

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

immediately for the FPF2143/47. FLAGB remains LO through

the Auto-Restart Time for the FPF2140/44. For the FPF2142/

46, FLAGB is latched LO and ON must be toggled to release it.

With the FPF2143/47, 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 guarantees that the current through the switch

doesn't exceed a maximum value while not limiting at less than

a minimum value. For the FPF2140/42/43 the minimum current

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

FPF2144/46/47 the minimum current is 400mA and the

maximum current is 800mA. The FPF2140/42/44/46 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 and the FLAGB pin will

activate to indicate that current limiting has occurred. The

FPF2143/47 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.

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.

Undervoltage Lockout

The undervoltage lockout turns-off the switch if the input

voltage drops below the undervoltage lockout threshold. With

the ON pin active the input voltage rising above the

undervoltage lockout threshold will cause a controlled turn-on of

the switch which limits current over-shoots.

Reverse Current Blocking

The entire FPF2140/47 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

current blocking feature is active when the load switch is turned

off.

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.

Thermal Shutdown

The thermal shutdown protects the die 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

temperature of the die drops below the threshold temperature.