Description of Operation

The FPF2300, FPF2302, and FPF2303 are dual-output current- limit switches designed to meet notebook computer, peripheral USB port, and point-of-load (POL) application power requirements. Dual-output current can be used where dual or quad USB ports are powered by hosts or self-powered hubs. The FPF230X family offers control and protection while providing optimum operation current for a safe design practice. The core of each switch is a typical 75mΩ (IN = 5.5V) P-channel MOSFET and a controller capable of functioning over an input operating range of 1.8-5.5V. The FPF230X family offers current limiting, UVLO (under-voltage lockout), and thermal shutdown protection per each switch. In the event of an over-current condition, the load switch limits the load to current limit value. The minimum current limit is set to 1100mA.

On/Off Control

The ON pin is active LOW for FPF2300/2/3 and controls the state of the switch. Pulling the ON pin continuous to LOW holds the switch in the ON state. The switch moves into the OFF state when the ON pin is pulled HIGH or if a fault is encountered. For all versions, an under-voltage on input voltage 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 FPF2300 and FPF2302 after a 10ms blanking time. The FPF2300 has an auto-restart feature that automatically turns the switch ON again after 504ms. For the FPF2302, the ON pin must be toggled to turn on the switch again. The FPF2303 does not turn off in response to an over-current condition, but remains operating in a constant-current mode as long as ON is enabled and the thermal shutdown or UVLO is not activated. The ON pin does not have a pull-down or pull-up resistor and should not be left floating.

startup blanking feature that prevents current faults related to startup transients from triggering the FLAGB output. The startup blanking feature is effective for the first 10ms (typical) following device turn-on via ON pin.

The FLAGB outputs are two open-drain MOSFETs that require a pull-up resistor on each FLAGB pin. FLAGB can be pulled HIGH to a voltage source other than input supply with maximum 5.5V. A 100KΩ pull-up resistor is recommended. When the ON pin is inac- tive, the FLAGB is disabled to reduce current draw from the supply. If the FLAGB is not used, the FLAGB can be connected to ground on the PCB.

.

ON

device wakeup

IN

device wakeup

FLAGB

RISE

TIME 90% VOUT

OUT

10% VOUT

ILOAD

ILIMIT

Figure 35. FLAGB Assertion in Under-Voltage Fault

Switch Limit Current Output-Dual — FPF2300/02/03

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. FPF230X family has dual-output load switches being housed in one package. The minimum current at which both switches start limiting the load current is set to 1100mA. The FPF2300 and FPF2302 have a blanking time of 10ms (typical), during which the switch acts as a constant current source. At the end of the blanking time, the switch is turned off. The FPF2303 has no current limit blanking period, so it remains in a constant current state until the ON pin of the affected switch is deactivated or the thermal shutdown turns off the switch.

Fault Reporting

Over-current, input under-voltage, and over-temperature fault conditions are signaled out by the FLAGB pin going LOW. A UVLO fault is reported on both FLAGB(A) and FLAGB(B) simultaneously, while over-current and over-temperature condition faults are reported independently. FPF2300 and FPF2302 have a current fault blanking feature that prevents over-current faults shorter than

the blanking time (tBLANK(Typ) = 10ms) from triggering the fault signal (FLAGB) output.

If the over-current condition persists beyond the blanking time, the FPF2300 pulls the FLAGB pin LOW and shuts the switch off. If the ON pin is kept active, an auto-restart feature releases the FLAGB pin and turns the switch on again after a 504ms auto-restart time (tRSTRT). If the over-current condition persists beyond the blanking time, the FPF2302 has a latch-off feature that pulls the FLAGB pin LOW and shuts the switch off. The switch is kept off and the FLAGB pin kept LOW until the ON pin is toggled. The FPF2303 responds to an overload condition by immediately pulling the FLAGB pin LOW and the switch remains in constant current mode until the output overload condition is removed. The FPF2303 has a

ON

VIN

VOUT

RL*ILMIT

ILOAD

ILIMIT

Over current

condtion

FLAGB

tRSTRT

tBLANK

Figure 36. FPF2300 FLAGB Reports While Entering

into an Over-Current Condition

Note:

6.An over-current condition signal loads the output with a heavy load current larger than ILIM value.

© 2009 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FPF2300/02/03 • Rev. 1.1.3

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