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NCP382

Fixed Current-Limiting Power-Distribution Switches

ON Semiconductor 

NCP382

FUNCTIONAL DESCRIPTION

Overview

The NCP382 is a dual high side power distribution

switches designed to protect the input supply voltage in case

of heavy capacitive loads, short circuit or over current. In

addition, the high side MOSFETs are turned off during

undervoltage or thermal shutdown condition. Thanks to the

soft start circuitry, NCP382 is able to limit large current and

voltage surges.

VOUTX

IOUTX

Thermal

Regulation

Threshold

IOCP

Timer

Regulation

Mode

Overcurrent Protection

NCP382 switches into a constant current regulation mode

when the output current is above the IOCP threshold.

Depending on the load, the output voltage is decreased

accordingly.

− In case of hot plug with heavy capacitive load, the

output voltage is brought down to the capacitor voltage.

The NCP382 will limit the current to the IOCP threshold

value until the charge of the capacitor is completed.

VOUTX

IOUTX

IOCP

Drop due to

capacitor charge

TOCP TREG

Figure 8. Short−Circuit

Then, the device enters in timer regulation mode, described

in 2 phases:

− Off−phase: Power MOSFET is off during TOCP to allow

the die temperature to drop.

− On−phase: regulation current mode during TREG. The

current is regulated to the IOCP level.

The timer regulation mode allows the device to handle

high thermal dissipation (in case of short circuit for

example) within temperature operating condition.

NCP382 stays in on−phase/off−phase loop until the over

current condition is removed or enable pin is toggled.

Remark: other regulation modes can be available for

different applications. Please contact our On Semiconductor

representative for availability.

Figure 6. Heavy Capacitive Load

− In case of overload, the current is limited to the IOCP

value and the voltage value is reduced according to the

load by the following relation:

VOUTX + RLOAD2 IOCP

(eq. 1)

VOUTX

IOUTX

IOCP x RLOAD

IOCP

Figure 7. Overload

− In case of short circuit or huge load, the current is

limited to the IOCP value within TDET time until the

short condition is removed. If the output remains

shorted or tied to a very low voltage, the junction

temperature of the chip exceeds TSDOCP value and the

device enters in thermal shutdown (MOSFET is

turned−off).

FLAG Indicator

The FLAG pin is an open−drain MOSFET asserted low

during overcurrent or overtemperature conditions. When an

overcurrent fault is detected on the power path, FLAG pin

is asserted low at the end of the associate deglitch time

(TFOCP). Thanks to this feature, the FLAG pin is not tied

low during the charge of a heavy capacitive load or a voltage

transient on output. The FLAG pin remains low until the

fault is removed. Then, the FLAG pin goes high at the end

of TFGL

Undervoltage Lock−out

Thanks to a built−in under voltage lockout (UVLO)

circuitry, the output remains disconnected from input until

VIN voltage is above VUVLO. This circuit has a VHYST

hysteresis witch provides noise immunity to transient

condition.

Thermal Sense

Thermal shutdown turns off the power MOSFET if the die

temperature exceeds TSD. A built-in hysteresis prevents the

part from turning on until the die temperature cools at

TRSD.

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