LM393: TI LM393DR output oscillation waveform issue

Hi Gary, 

you mention hysteresis, but I don't see any feedback resistor on the schematic which may be why you're seeing the chatter.

Here's an example with some of the parameters as well as a hysteresis calculator for inverting config you can use.

5861.Comparator Hysteresis Tool.xlsx

Let me know if you have further questions.

Best,

Michael

Hello Michael,

We have used feedback resistor R3964 in the circuit and verified the hysteresis values VA1 and VA2, but oscillations occur regardless of the state transitions at VA1 or VA2

According to the calculated values, there shouldn't be any oscillation. There is no interference at the Iinput voltage of IN2- either. Could the cause of this issue be the IC itself?

Thanks

Hi Gary,

Try removing C28.

Adding a capacitor to the positive node when applying hysteresis creates a delay - which can cause "bursting" or outright cancellation of the hysteresis.

Hello Paul,

We tried removing C28, but oscillations still occur at the switching point.

Could the cause of this issue be the IC itself?

Do you have any other suggestions or a better P2P comparator recommendation?

Thanks

Hi Gary,

What is the comparator supply voltage??

Remember that the LM393 has a Vcc-2V input limit. If you are running it at 3.3V supply, the highest input voltage should be 1.3V. If the input voltages are floating around 2.3V, then you will get some funny behavior.

Please see the LM339 family appnote, section 5.4:

Application Design Guidelines for LM339, LM393, TL331 Family Comparators

If you want to try another device:

1. If your supply voltage is 5V and below, try the LM393LV.
2. If your supply voltage is above 5V, try the TLV1822.