LM393A: Do we need to add the feedback circuit on LM393A?

Ke-Hsu Chen

Prodigy 50 points

Part Number: LM393A
Other Parts Discussed in Thread: LM393LV, TLV7041, TLV3201

Tool/software:

We have some application problems and need your help to clarify.

According to the datasheet, it seems that we don't need to add the feedback circuit on LM393A.

Can we remove the 100Kohm resistor as shown below? Are there any impacts if we remove this resistor?

Thanks.

KeHsu

3 months ago

0 Clemens Ladisch 3 months ago

Guru 316960 points

The datasheet does not say this. And in general, you do want hysteresis, so you need the feedback resistor. Without hysteresis, slow input signals can lead to oscillations.

0 Ron Michallick 3 months ago

TI__Guru**** 164976 points

Hello KeHsu,

The common mode voltage should stay under VCC-2V, which is 1.3V, pin 3 voltage should be lowered.

Alternative device, LM393LV is rail to rail input , so it is easier to use.

0 Paul Grohe 3 months ago

TI__Guru 60476 points

Hi KeHsu,

If the input signal is slow moving (like temperature change or battery charging) or noisy, then hysteresis is recommended. Otherwise the output can "chatter" when right at the threshold when it slowly crosses. It just depends on how much "chatter" you can tolerate.

For more information, see the following appnotes:

Comparator with and without hysteresis circuit - SBOA219

Inverting comparator with hysteresis circuit - SNOA997

Non-Inverting Comparator With Hysteresis Circuit - SBOA313

0 Ke-Hsu Chen 3 months ago in reply to Paul Grohe

Prodigy 50 points

Hi Paul

Thanks for reply.

When I try to open the link of "Comparator with and without hysteresis circuit - SBOA219", it shows "We can't find this page" error message.

The other two links are OK, but I found that they are the design guide for TLV7041.

Could you help to provide the design guide for LM393A? Thank you.

0 Clemens Ladisch 3 months ago in reply to Ke-Hsu Chen

Guru 316960 points

Comparator with and without hysteresis circuit - SBOA219

Application Design Guidelines for LM339, LM393, TL331 Family Comparators

The LM393A and TLV7041 have open-collector/open-drain outputs; they behave the same. (The TLV3201 has a push/pull output and does not need a pull-up resistor.)

0 Paul Grohe 3 months ago in reply to Ke-Hsu Chen

TI__Guru 60476 points

Sorry...There was a typo in the link. It will be fixed in the next release.

Thank you for uncovering it!

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LM393A: Do we need to add the feedback circuit on LM393A?