2017. 03. 02

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FC9521

Revision No : 0

VIN Under-Voltage Lockout (UVLO)

The FC9521 power switches have a built-in under-voltage lockout

circuit to keep the output shu�ng off un�l internal circuitry is

opera�ng properly. The UVLO circuit has hysteresis and a de-glitch

feature so that it will typically ignore undershoot transients on the

input. When input voltage exceeds the UVLO threshold, the output

voltage starts a so�-start to reduce the inrush current.

Power Switch

The power switch is an N-channel MOSFET with a low RDS(ON). The

internal power MOSFET does not have the body diode. When IC is off,

the MOSFET prevents a current flowing from the VOUT back to VIN and

VIN to VOUT.

Current-Limit Protec�on

The FC9521 power switches provide the current- limit protec�on

func�on. During current-limit, the devices limit output current at

current limit threshold. For reliable opera�on, the device should not be

operated in current-limit for extended period.

Short-Circuit Protec�on

When the output voltage drops below 1.5V, which is caused by an

over-load or a short-circuit, the devices limit the output current down

to a safe level. The short-circuit current limit is used to reduce the

power dissipa�on during short-circuit condi�ons. If the junc�on

temperature reaches over-temperature threshold, the device will enter

the thermal shutdown.

ISET

ISET pin can set the current limit by Riset:

ILim=120k*1.2V/Riset

Enable/Disable

Pull the EN below 0.8V will disable the device, and pull EN above 2V will

enable the device. When the IC is disabled, the supply current is

reduced to less than 1μA. The enable input is compa�ble with both TTL

and CMOS logic levels. The EN pin cannot be le� floa�ng.

Over-Temperature Protec�on

When the junc�on temperature exceeds 140℃, the internal thermal

sense circuit turns off the power FET and allows the device to cool

down. When the device’s junc�on temperature cools by 20℃, the

internal thermal sense circuit will enable the device, resul�ng in a

pulsed output during con�nuous thermal protec�on. Thermal

protec�on is designed to protect the IC in the event of over

temperature condi�ons. For normal opera�on, the junc�on

Func�on Descrip�on