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KIC6971F/MF

Revision No : 2

Functional Description

1. Over-current and Short Circuit Protection

An internal sensing FET is employed to check for over-current conditions. Unlike current-sense resistors, sense FETs do not

increase the series resistance of the current path. When an over-current condition is detected, the device maintains a constant

output current and reduces the output voltage accordingly. Complete shutdown occurs only if the fault stays long enough to

activate thermal limiting.

2. Thermal Protection

Thermal protection prevents the IC from damage when the die temperature exceeds safe margins. This mainly occurs when

heavy-overload or short-circuit faults are present for extended periods of time. The KIC6981F/MF implements a thermal

sensing to monitor the operating junction temperature of the power distribution switch. Once the die temperature rises to

approximately 150

°C, the Thermal protection feature gets activated as follows: The internal thermal sense circuitry turns the

power switch off and the FLG output is asserted thus preventing the power switch from damage. Hysteresis in the thermal sense

circuit allows the device to cool down to approximately 25

°C before the output is turned back on. This built-in thermal

hysteresis feature is an excellent feature, as it avoids undesirable oscillations of the thermal protection circuit. The switch

continues to cycle in this manner until the load fault is removed, resulting in a pulsed output. The FLG open-drain output is

asserted when an over-current occurs with 7-ms deglitch.

3. Under-Voltage Lockout (UVLO)

Under-voltage lockout function (UVLO) guarantees that the internal power switch is initially off during start-up. The UVLO

functions only when the switch is enabled. Even if the switch is enabled, the switch is not turned ON until the power supply has

reached at least 2.2V. Whenever the input voltage falls below approximately 2.2V, the power switch is turned off. This

facilitates the design of hot-insertion systems where it is not possible to turn off the power switch before input power is

removed.

4. Reverse Current Protection

In a normal MOSFET switch, current can flow in reverse direction (from the output side to the input side) when the output side

voltage is higher than the input side, even when the switch is turned off. A reverse-current blocking feature is implemented in

the KIC6981F/MF to prevent such back currents. This circuit is activated by the difference between the output voltage and the

input voltage. When the switch is disabled, this feature blocks reverse current flow from the output back to the input.

5. Discharge Function

When enable is de-asserted, the discharge function is active. The output capacitor is discharged through an internal NMOS that

has a discharge resistance of 100

Ω. Hence, the output voltage drops down to zero. The time taken for discharge is dependent

on the RC time constant of the resistance and the output capacitor.

6. FLG Response

The FLG open-drain output goes active low for any of the two conditions: Over-Current or Over-Temperature. The time from

when a fault condition is encountered to when the FLG output goes low is 7-ms (TYP). The FLG output remains low until both

over-current and over-temperature conditions are removed. Connecting a heavy capacitive load to the output of the device can

cause a momentary Over-current condition, which does not trigger the FLG due to the 7-ms deglitch timeout. The

KIC6981F/MF is designed to eliminate erroneous Over-current reporting without the need for external components, such as an

RC delay network.