• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 47 subscribers
  • Views 4275 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AMC1100: output of AMC 1100 according to app note SLAA552

Michael Zartarian
Prodigy 30 points
Part Number: AMC1100
Other Parts Discussed in Thread: AMC1200

hi everyone,

I am following this app note to use the AMC1100 for input voltage sensing off mains: http://www.ti.com/lit/an/slaa552/slaa552.pdf

Specifically, I have built up this circuit here and had it fabbed on a PCB (no breadboard) and am now testing it out:

When looking at the output at 'ACMAINSENSE' I am seeing a signal much smaller than what I would expect for the gain of 8x.  My questions are:

- is the app note correct to leave the VOUTN completely un terminated?

- i am using a 5V supply on the isolated side instead of 3.3V in the app note.  would this make any difference in the application?

- i am omitting the zero cross detector in favor of a buffer op-amp to then send the analog voltage to an single-ended ADC that is muxed with many other sensor signals.  would it be better to receive the output of the AMC1100 with an op-amp differentially?

This is my first use of an isolation op-amp, so I apologize for any oversights on my parts.

Thank You,

Mike

Thank You!

  • 0
    TI__Guru**** 181901 points
    Hi Mike,

    Welcome to the e2e Forum! Can you tell us what voltages are going into the AMC1100 and what you see at the output? Most applications using the AMC1100 or the AMC1200 would utilize the entire differential output range of the device. The authors of this application note decided to use only half the output span, so in that case leaving the VOUTN un-terminated is fine.

    The only real difference between using 3.3V or 5V on VDD2 is the output common mode voltage (see Figure 26). If you are driving into a single ended ADC, my suggestion would be that you take the full output swing of the AMC1100 and do a differential to single output conversion.
  • 0 in reply to Tom Hendrick
    Prodigy 30 points

    Hi Tom,

    Thank you for the reply and welcome!

    I had a strange build issue or bad chip cause my problem.  I remelted some of the connections and replaced the chip and all is well.  The block was marginally working before, but now it works perfectly as per the specs in the whitepaper.

    I'll revise my design to receive the output differentially into an op amp to convert to single ended - thank you for the advice.  Luckily I am not so cost constrained that it's an issue.   

    Sincerely,

    Mike

  • 0 in reply to Michael Zartarian
    Prodigy 30 points

    A note for those in the future reading this - I ended up needing to use the AMC1100 single ended since I don't have a split supply and therefore can't easily run a differential receiver.  This is fine for my application as I am using analog processing downstream to go from an AC waveform to RMS output expressed in DC.  

    Thanks again,

    Mike

  • 0 in reply to Michael Zartarian
    TI__Guru**** 181901 points
    Thanks for the note Mike! Feel free to let us know if you have any additional questions.