LM393-N: Input Resistance of the IC

Raj Narnoli

Part Number: LM393-N
Other Parts Discussed in Thread: LM393

I want to make sure that the input impedance of the input pins is high enough that it won't be affected by the voltage divider circuit I have designed here in the attached snapshot.

over 3 years ago

0 kai klaas69 over 3 years ago

Guru 140200 points

Hi Raj,

the input bias current of 100nA of LM393N causes a voltage drop of 0.1V across R9. I guess that's not what you want?

I would remove R9 and R10 and split R8 suitedly :-)

Do you need help with this?

Kai

0 kai klaas69 over 3 years ago in reply to kai klaas69

Guru 140200 points

And add hysteresis :-)

Kai

0 Raj Narnoli over 3 years ago in reply to kai klaas69

Intellectual 320 points

Yes Sure..... I would like to install 0603 resistors hence I split the values accordingly. Please help me with suitable values. The powering points MC+ And MC- are at 530V maximum and I am controlling Precharge and Accumulator Isolation Relay with this circuit. LM393 should change logic levels at 90% of the Battery Voltage.

0 Joe Vanacore over 3 years ago in reply to Raj Narnoli

TI__Genius 11845 points

Hi Raj,

Depending on your desired resistor tolerance, I would suggest splitting R8 into resistances as close to a 2.45kOhm and a 24.54kOhm. (So maybe a 2.44kOhm and a 24.6kOhm?)

To maintain the 10/11 ratio of the voltage seen at the bottom of R7, the ~2.45kOhm should be placed on the top of the voltage divider and the ~24.54kOhm should be placed on the bottom of the divider and connected to GND.

The voltage across the ~24.54kOhm should feed the "NEG_A" input to the LM393.

Would you still like to implement external hysteresis?

Regards,

Joe

Amplifiers

Amplifiers forum

LM393-N: Input Resistance of the IC