Pplication. refer to figure 3, R inverter. figure 3 shows th, An258 – Cirrus Logic AN258 User Manual

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AN258

AN258REV2

Figure 3. Oscilloscope View of the Red LED RC Circuit, R2 = 120 k

Ω

The second part of the circuit causes a simulated manual reset button press to occur. The RC on the MR
pin of the voltage monitor IC generates a pulse from the logic-zero level output of the Schmitt-trigger in-
verter. The generation of this pulse is very important. If the pulse is not present, the voltage monitor will
continuously drive the POR signal and keep the EP93xx in reset, which keeps the first RC circuit charging
and the red LED illuminated.

The operation of second part of the circuit relies on the fact that there is a pull-up resistor on the MR pin
inside the voltage monitor IC. Refer to Figure 4 for an oscilloscope view of the RC circuit at the MR pin.