LM9061, LM9061-Q1

SNOS738H – APRIL 1995 – REVISED JANAURY 2015

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Feature Description (continued)

especially when driving inductive type loads. A minimum value of 1 k

Ω will protect the pin from transients ranging

from

current for the input stage transfers from the Sense pin to the Threshold pin, thereby changing the voltages

present at the inputs to the comparator. For consistent switching of the comparator right at the desired threshold

point, the voltage drop that occurs at the noninverting input (Threshold) should equal, or exceed, the rise in

voltage at the inverting input (Sense).

larger than 0.1 µF, and is not needed for most applications.

7.3.5 Delay Timer

To allow the MOSFET to conduct currents beyond the protection threshold for a brief period of time, a delay

timer function is provided. This timer delays the actual latching OFF of the MOSFET for a programmable interval.

This feature is important to drive loads which require a surge of current in excess of the normal ON current upon

start-up, or at any point in time, such as lamps and motors. Figure 15 details the delay timer circuitry. A capacitor

connected from the Delay pin 8, to ground sets the delay time interval. With the MOSFET turned ON and all

conditions normal, the output of the protection comparator is low and this keeps the discharge transistor ON. This

transistor keeps the delay capacitor discharged. If a surge of load current trips the protection comparator high,

the discharge transistor turns OFF and an internal 10-µA current source begins linearly charging the delay

capacitor.

comparator threshold of typically 5.5 V, the output of the comparator will go high to set a flip-flop and immediately

latch the MOSFET OFF. It will not restart until the ON/OFF Input is toggled low then high.

where

•

•

(6)

Charging of the delay capacitor is clamped at approximately 7.5 V which is the internal bias voltage for the 10 µA

current source.

Figure 15. Delay Timer

16

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