Help with reading schematic

Thread Starter

Manish Chowdhary

Joined Jul 29, 2017
5
upload_2019-4-9_12-24-10.png

I am posting a part of schematics here, this refers to voltage monitor circuit , I know that this circuit monitors 1.2V , 1.6V and 3.3V
( not shown in the figure ) and only if all signals are up, it sends PGOOD indication.
I need some help to understand what the encircled circuits elements are doing here?
 

Alec_t

Joined Sep 17, 2013
11,504
1 is a low-pass filter circuit to smooth the voltage fed to pin 7 from the 3.3V supply being monitored. 3 is a comparator circuit. There will be a reference voltage (threshold) on pin 6. When the voltage on pin 7 is below the reference voltage the comparator output will be low. 2 is a feedback resistor which helps to keep the pin 7 voltage low. When the pin 7 voltage goes above the reference voltage the output (pin 1) of 3 goes high and the feedback resistor now helps to keep the pin 7 input high. This positive feedback arrangement ensures a snap action of the comparator so that minor voltage variations don't result in dithering.
The outputs of the three comparator circuits are 'wire-OR'ed', so that any one of the supplies being below threshold will be recognised as a 'power not good' signal.
 
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