Datasheet

LM9061

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SNOS738F –APRIL 1995–REVISED APRIL 1995

MINIMUM DELAY TIME

A minimum delay time interval is required in all applications due to the nature of the protection circuitry. At the

instant the MOSFET is commanded ON, the voltage across the MOSFET, V

, is equal to the full load supply

voltage because the source is held at ground by the load. This condition will immediately trip the protection

comparator. Without a minimum delay time set, the timing comparator will trip and force the MOSFET to latch-

OFF thereby never allowing the load to be energized.

To prevent this situation a delay capacitor is required at pin 8. The selection of a minimum capacitor value to

ensure proper start-up depends primarily on the load characteristics and how much time is required for the

MOSFET to raise the load voltage to the point where the Sense input is more positive than the Threshold input

START-UP

). Some experimentation is required if a specific minimum delay time characteristic is desired.

Therefore:

(7)

In the absence of a specific delay time requirement, a value for C

DELAY

of 0.1 µF is recommended.

OVER VOLTAGE PROTECTION

The LM9061 will remain operational with up to +26V on V

. If V

increases to more than typically +30V the

LM9061 will turn off the MOSFET to protect the load from excessive voltage. When V

has returned to the

normal operating range the device will return to normal operation without requiring toggling the ON/OFF input.

This feature will allow MOSFET operation to continue in applications that are subject to periodic voltage

transients, such as automotive applications.

For circuits where the load is sensitive to high voltages, the circuit shown in Figure 19 can be used. The addition

of a zener on the Sense input (pin 1) will provide a maximum voltage reference for the Protection Comparator.

The Sense resistor is required in this application to limit the zener current. When the device is ON, and the load

supply attempts to rise higher than (V

ZENER

+ V

THRESHOLD

), the Protection comparator will trip, and the Delay

Timer will start. If the high supply voltage condition lasts long enough for the Delay Timer to time out, the

MOSFET will be latched off. The ON/OFF input will need to be toggled to restart the MOSFET.

Figure 19. Adding Over-Voltage Protection

Product Folder Links: LM9061