DS1236

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NON-MASKABLE INTERRUPT

microprocessor. A precision comparator monitors the voltage level at the IN pin relative to a reference

generated by the internal band gap. The IN pin is a high-impedance input allowing for a user-defined

sense point. An external resistor voltage divider network (Figure 6) is used to interface with high voltage

signals. This sense point may be derived from the regulated 5-volt supply or from a higher DC voltage

for R1 and R2 can be determined by the equation as shown in Figure 6. Proper operation of the DS1236

this equation is to select a value for R2 high enough to keep power consumption low, and solve for R1.

The flexibility of the IN input pin allows for detection of power loss at the earliest point in a power

RST

.

to the active state for a minimum of 200

domain hysteresis. That is, the monitored supply is sampled periodically at a rate determined by an

internal ring oscillator running at approximately 30 kHz (33

μs/cycle). Three consecutive samplings of

must be below the voltage sense point for approximately 100

μs or the comparator will reset. In this way,

power supply noise is removed from the monitoring function, preventing false trips. During a power-up,

μs minimum to 500 μs maximum, depending

is tied to ground during power-up, the internal time-out will result in a pulse of 200

μs minimum to 500

μs maximum. In contrast, if the IN pin is tied to V

power-up. This is of no consequence, however, since an RST will be active.