1
\$\begingroup\$

I am putting the output of a current sensing IC (ACS70331) into an ADC (LTC2373). I am that a buffer on the input to an ADC is often required if the output of the source is high impedance. However, I am not sure how to find the cutoff where that becomes necessary for the ADC and I do not see the impedance on the current sensor data sheet.

I have some guesses that you could look at the source current (0.4mA) of the current sensor and calculate the dV/dt of the input capacitance of the ADC input. I am looking for confirmation if that is the proper approach for this type of problem.enter image description here

\$\endgroup\$
4
  • 1
    \$\begingroup\$ Generally the correct approach yes. \$\endgroup\$
    – Andy aka
    Oct 30, 2020 at 18:14
  • \$\begingroup\$ @Andyaka How would I know what is "fast enough" for the dV/dt? The ADC samples at 1MS/s, if I am expecting a 2V signal should I be able to hit that point in a single sample? So 2V/us? \$\endgroup\$
    – MaxwellEE
    Oct 30, 2020 at 18:44
  • 1
    \$\begingroup\$ The devil is in the detail for sure so try using a simulator. \$\endgroup\$
    – Andy aka
    Oct 30, 2020 at 18:47
  • 1
    \$\begingroup\$ I am looking for confirmation if that is the proper approach for this type of problem. - my comment is not a full answer because that is not what you asked for. \$\endgroup\$
    – Andy aka
    Oct 30, 2020 at 18:48

1 Answer 1

1
\$\begingroup\$

The datasheet for the ACS70331 says it can drive 100pF and maintain stability. But in order to maintain the 1Mhz bandwidth, the capacitive load can be no greater than 50pF. The sampling capacitor for the LTC2373 is 75pF.

You can run it without a voltage follower and be fine. But since you want to maintain the 1Mhz bandwidth, you will need to use a voltage follower.

\$\endgroup\$

Your Answer

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

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