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FPF2193

Full-Function Load Switch with Adjustable Current Limit

ON Semiconductor 

Functional Description

The FPF2193, FPF2194, and FPF2195 are current-

limited sw itches 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

w ide input operating range of 1.8- 5.5 V. The controller

protects against system malfunctions through current

limiting, under-voltage lockout, and thermal shutdow n.

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 sw itch. When ON is

HIGH, the sw itch is in ON state. Activating ON

continuously holds the sw itch 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 sw itch. In addition,

excessive currents cause the sw itch to turn off in the

FPF2193 and FPF2194. The FPF2193 has an auto-

restart feature that automatically turns the sw itch on again

after 450 ms. For the FPF2194, the ON pin must be

toggled to turn the sw itch 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 shutdow n 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, w hile 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 betw een VIN and FLAGB. During

shutdow n, the pull-dow n on FLAGB is disabled to reduce

current draw f rom the supply.

Current Limiting

The current limit ensures that the current through the

sw itch doesn't exceed a maximum value, w hile not

limiting at less than a minimum value. The current at

w hich 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 w hich the

sw itch acts as a constant current source. At the end of

the blanking time, the sw itch 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 shutdow n turns off the sw itch.

For preventing the sw itch from large pow er dissipation

during heavy load, a short-circuit detection feature is

introduced. Short-circuit condition is detected by,

observing the output voltage. The sw itch is put into short-

circuit current-limiting mode if the sw itch is loaded w ith a

heavy load. When the output voltage drops below V SCTH,

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 pow er 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 sw itch is removed from short-circuit

current-limiting mode and the current limit is set to the

current limit value.

Unde r-Voltage Lockout (UVLO)

The under-voltage lockout turns the sw itch 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 sw itch, w hich limits current over shoot.

Thermal Shutdown

The thermal shutdow n protects the die from internally or

externally generated excessive temperatures. During an

over-temperature condition, FLAGB is activated and the

sw itch is turned off. The sw itch 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

pow er design, this is an important feature to protect the

USB host from being damaged due to reverse current

flow on VBUS.

When the load sw itch is OFF, no current flow s from the

output to the input. If the sw itch is turned on and the

output voltage is greater than input voltage, this feature is

activated and turns off the sw itch. This prevents any

current flow from output to input. The reverse-current

blocking feature is deactivated if the V OUT - VIN is smaller

than a typically 50 mV threshold. During this time, some

current (50 mV/RON) flow s 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.

w here:

tdON = Delay On Time

tR = VOUT Rise Time

tON = Turn-On Time

tdOFF = Delay Off Time

tF = VOUT Fall Time

tOFF = Turn-Off Time

Tim ing Diagram

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