TL081H: Cost effective voltage follower opamp

Francisco Fernandez

Part Number: TL081H
Other Parts Discussed in Thread: LM321LV, TLV9001

Tool/software:

Hello,

We are trying to find a simple 1 channel cost effective voltage follower opamp.

We intend to connect a voltage divider to the noninverting input and use the opamp output to read the voltage with the ADC of our MCU.

The output of the voltage divider witll range between 0,7V and 3,3V.

Could you make a recommendation? We need it to be cost effective and small size if possible.

Thanks

6 months ago

+1 Clemens Ladisch 6 months ago

Guru 289750 points

What are your supply voltages?

The TL081H will not be able to go as low as 0.7 V above its negative supply.
If you have a 5 V supply and if the SC-70 package is small enough, the LM321LV would be cheapest.
If you have only a 3.3 V supply or if you need a package as small as X2SON, use the TLV9001.

0 Francisco Fernandez 6 months ago in reply to Clemens Ladisch

Prodigy 130 points

Main voltage supply which we want to read ranges from 7VDC to 32VDC

We have 6VDC and 3.3VDC power rails within the PCB

0 Clemens Ladisch 6 months ago in reply to Francisco Fernandez

Guru 289750 points

All the cheap opamps that support 0.7 V signals do not go above 5 V, so you have to use the 3.3 V rail.

0 Francisco Fernandez 6 months ago in reply to Clemens Ladisch

Prodigy 130 points

Thanks Clemens for your prompt and accurate answers.

Why cant the LM321LV work with the 3.3VDC power rail? I can read within the datasheet that operational supply is from 2.7V to 5.5V

0 Clemens Ladisch 6 months ago in reply to Francisco Fernandez

Guru 289750 points

It does not have rail-to-rail inputs; its input common-mode voltage range ends 1 V below the positive supply.

0 Francisco Fernandez 6 months ago in reply to Clemens Ladisch

Prodigy 130 points

Thanks, you resolved our questions

Considering everything we talked about would you recommend using protection shottky diodes like BAT54 on INPUT+ or output/INPUT

Any other recommendation for protection porpose?

0 Clemens Ladisch 6 months ago in reply to Francisco Fernandez

Guru 289750 points

If transient voltages can happen on those traces, then clamping diodes stronger than the internal ones can make sense.

0 Francisco Fernandez 6 months ago in reply to Clemens Ladisch

Prodigy 130 points

Thank you Clemens,

I know, that is why we include the external diodes in our design. But my question was:

- Would you include the external diodes on the IMPUT+ of the opamp?

- Would you include the external diodes on the OUTPUT of the opamp?

Thanks.

+1 Ron Michallick 6 months ago in reply to Francisco Fernandez

TI__Guru**** 154986 points

Hello Francisco,

If the ADC uses 3.3V, then the op amp should also use this supply. If the ADC recommends an input capacitor, the add a RC output filter that works well with ADC and is stable with the op amp. If response time (speed) matters then check that RC filter is ready for next sampling

If the input divider resistors are relatively high resistance and a small capacitor is on non-inverting input to ground then that should be good enough protection unless ESD or EOS is likely to happen. Clamp diodes can be helpful but watch that their leakage doesn't affect the signal voltage. An op amp with IN to VCC diodes can be helpful to limit voltage, if divider resistance is high then the input current should be negligible.

TLV9001 is a good choice.

0 Francisco Fernandez 6 months ago in reply to Ron Michallick

Prodigy 130 points

Thanks for the detailed answer, it’s truly appreciated

Regards

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TL081H: Cost effective voltage follower opamp