Fairchild FPF2300, FPF2302, FPF2303 Input Capacitor, Under-VoltageLockout (UVLO), Reverse Current Blocking, Thermal Shutdown, Output Capacitor, Figure 37. FPF2300 FLAGB While and Over-Current

VIN

automatically turns on again. To avoid unwanted thermal oscillations, a 10°C (typical) thermal hysteresis is implemented between thermal shutdown entry and exit temperatures.

If output of both switches are connected together and an excessive load current activates thermal protection of both, the controller can shut down the switches after both FLAGB outputs

FPF2300/02/03

VOUT

ILOAD

ILIMIT

Over current condtion

FLAGB

Startup tBLANK

down Shut

Thermal

Device	Cools
	Cools
	Off

go LOW and turn on both channels again. This provides simultaneous switch turn on. Thermal protection is for device protection and should not be used as regular operation.

Input Capacitor

To limit the voltage drop on the input supply caused by transient inrush currents when the switch is turned on into discharged load capacitors or a short-circuit; an input capacitor, CIN, is recommended between IN and GND. The FPF2310/2/3/3L

Output-Dual —

Figure 37. FPF2300 FLAGB While and Over-Current

Condition is Applied

Note:

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

Under-Voltage Lockout (UVLO)

The under-voltage lockout feature turns off the switch if the input voltage drops below the under-voltage lockout threshold. With the ON pin active (ON pin pulled LOW), the input voltage rising above the under-voltage lockout threshold causes a controlled turn-on of the switch and limits current overshoot. If a device is in UVLO condition, both FLAGBs go LOW and indicate the fault condition. The device detects the UVLO condition when input voltage goes below UVLO voltage, but remains above 1.3V (typical).

Reverse Current Blocking

Each switch of FPF2300/2/3 has an independent 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 that protects the USB host from being damaged due to reverse current flow on VBUS. To activate the reverse current blocking, the switch must be in OFF state (ON pins inactivated) so that no current flows from the output to the input. The FLAGB operation is independent of the reverse current blocking and does not report a fault condition if this feature is activated.

Thermal Shutdown

The thermal shutdown protects the device from internally or externally generated excessive temperatures. Each switch has an individual thermal shutdown protection function and operates independently as adjacent switch temperatures increase above 140°C. If one switch is in normal operation and shutdown protection of second switch is activated, the first channel continues to operate if the affected channel's heat stays confined. The over-temperature in one channel can shut down both switches due to rapidly generated excessive load currents resulting in very high power dissipation. Generally, a thermally improved board layout can provide heat sinking and allow heat to stay confined and not affect the second switch operation.

During an over-temperature condition, the FLAGB is pulled LOW and the affected switch is turned off. If the temperature of the die drops below the threshold temperature, the switch

features a fast current limit response time of 20μs. An inrush current (also known as surge current) could occur during the current limit response time while the switch is responding to an over-current condition caused by large output capacitors. A 10μF ceramic capacitor, CIN, is required to provide charges for the inrush current and prevent input voltage drop at turn on. Higher values of CIN can be used to further reduce voltage drop.

Output Capacitor

A0.1μF to 1μF capacitor, COUT, should be placed between the OUT and GND pins. This capacitor prevents parasitic board inductances from forcing output voltage below GND when the switch turns off. This capacitor should have a low dissipation factor. An X7R MLCC (Multilayer Ceramic Chip) capacitors is recommended.

For the FPF2300 and FPF2302, the total output capacitance

needs to be kept below a maximum value, COUT(MAX), to prevent the part from registering an over-current condition

beyond the blanking time and shutdown. The maximum output capacitance for a giving input voltage can be determined from the following:

COUT(MAX)	=	ILIM(MIN) x tBLANK(MIN)	(1)
		VIN

For example, in a 5V application, COUT(MAX) can be determined as:

COUT(MAX)(IN = 5V) =	1.1A x 5ms	(2)
		(2)
	5
	5
=	1.1mF

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