1
\$\begingroup\$

I built a simple non inverting op amp amplifier with 2 resistors and a TS972IN powered between 0-5V but my output was always set to 5V. I tried several others Op Amp, others resitors and I also moved my circuit elsewhere (I'm working with a breadboard) and none of this changed anything. In order to solve my issue, I decided to build something even simpler, a voltage follower but I have the same behavior, the output stays to 5V...

My circuit with the pinout I use:

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$
2
  • \$\begingroup\$ that's an OPamp that's explicitly deprecated by its manufacturer; while certainly fine for learning and prototyping, be aware that it might not be possible to get any quantity of it in the future. \$\endgroup\$
    – Marcus Müller
    Dec 31, 2019 at 15:55
  • \$\begingroup\$ According to the datasheet pl.mouser.com/datasheet/2/389/ts971-957361.pdf, The allowed input voltage range lies between 1.35V...3.65V. \$\endgroup\$
    – G36
    Dec 31, 2019 at 15:59

1 Answer 1

Reset to default
4
\$\begingroup\$

Data sheet, page 5:

Vicm Common mode input voltage range VDD + 1.15 to VCC - 1.15 V

You're trying to make it work VDD + 0 to VCC - 0 V; that won't do. This is just what is known as Latch-up behaviour.

You have a rail-to-rail output opamp. What you'd need to have is a rail-to-rail input and output (RRIO) opamp for this to work.

\$\endgroup\$
4
  • \$\begingroup\$ Many thanks I thought I was going insane, I'll pay attention to this for future circuits ! You mentionned this part is deprecated ,can you advise me an RRIO opamp to play with ? (I'm trying to amplify a 162KHz signal received by a tuned ferite rod) \$\endgroup\$
    – Robert Dubois
    Dec 31, 2019 at 16:18
  • \$\begingroup\$ why would you need the full 0 to 5V input range for that? Just bias your input to say 2.5 V? \$\endgroup\$
    – Marcus Müller
    Dec 31, 2019 at 16:25
  • \$\begingroup\$ Ok I see I can keep the TS972 for experimenting by working around VCC/2, to respect VDD + 1.15 to VCC - 1.15 V range. \$\endgroup\$
    – Robert Dubois
    Dec 31, 2019 at 16:27
  • \$\begingroup\$ exactly! Just use a rather high-ohmic voltage dividers (maybe 2× 1 MΩ) to put your antenna-originating signal up to 2.5 V (voltage divider: VCC-1MΩ-(x)-1MΩ-GND, couple in the antenna via a capacitor to (x), connect your non-inverting opamp input to (x). \$\endgroup\$
    – Marcus Müller
    Dec 31, 2019 at 16:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.