• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 46 subscribers
  • Views 397 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.

Correct way of connecting the LOG112 logarithmic amplifier to an ADC (like the ADS8505).

Jesus Vasquez
Prodigy 80 points
Other Parts Discussed in Thread: LOG112, ADS8505

Hello everybody. I’m designing a system for acquiring a current signal using the logarithmic amplifier LOG112. I would like to use a 16-bit ADC like the ADS8505. However, I’m not very sure how to interconnect these two devices: is enough to connect the output of the LOG112 to the input (resistance network as shown on fig. 21 on pag. 10 of its datasheet)? Or should I use an operational amplifier (voltage follower) in between both of the for impedance couple? I’m using the LOG112 internal operational  for scaling my current range to the desired output voltage (as shown on the figure on the first page of its datasheet). I haven’t found any information about this on the technical documentation.

 

Thank you very much for your help in advance.

  • 0
    TI__Genius 12335 points

    Hello Jesus,

    The output amplifier of the LOG112 (A3) is capable of driving the input of an ADC. The characteristics of this amplifier can be found in the datasheet specification tables on page 4 in the "OP AMP, A3" section. Notice that the minimum acquisition time of the ADS8505 is 1.8uS, however the output amplifier of the LOG112 requires 16uS for settling to .01% (approximately 12 bit settling) in the case of a step input. Therefore you would need to lengthen the acquisition time of the ADS8505 to allow for settling with transient input signals.

  • 0 in reply to John Caldwell
    Prodigy 80 points

    Hello John,

    Thank you very much for your answer and also for your indication on the acquisition timing. I will consider it on my design. Thanks!

    Jesus