1
\$\begingroup\$

I'm currently working on a project that will incorporate an AD7124-8 ADC, which as far as I understand can accept true bipolar inputs when provided a split supply. I tried to dig around for an app note or reference design from AD on this, but couldn't seem to find anything.

My questions are

  • What is the typical way to go about providing such a supply?
  • What parameters do I need to pay close attention to?
  • Will I also need to provide a separate split reference?

My current approach is to use a charge pump to convert 3.3V to -3.3v, then an LDO to get -1.8V;

  • If this is the right approach, can I use the same LDO on both positive and negative rails?
\$\endgroup\$
4
  • 1
    \$\begingroup\$ Are you sure those voltages are correct for that ADC? Linear regulators cannot reverse polarity. "separate split reference?" Read the datasheet. \$\endgroup\$
    – DKNguyen
    Aug 26, 2021 at 13:18
  • \$\begingroup\$ I've used a charge pump and (negative) LDO to digitize bipolar signals with only USB +5v. Pick LDOs with high PSRR at the charge pump switching frequency. \$\endgroup\$ Aug 26, 2021 at 13:52
  • \$\begingroup\$ @DKNguyen, I have read the datasheet, it's very unclear and there are no obvious reference designs/app notes for a split power supply at +/-1.8V. My question about the reference was: If I have +/-1.8V for AVDD and AVSS then do I need to find voltage references to supply REFIN1+ and REFIN1-? The datasheet is also painfully unclear on this. \$\endgroup\$
    – Sensors
    Aug 26, 2021 at 14:07
  • \$\begingroup\$ @Sensors It isn't unclear. You just check the reference voltage required to see if it is actually bipolar or not. \$\endgroup\$
    – DKNguyen
    Aug 26, 2021 at 14:16

1 Answer 1

1
\$\begingroup\$
  1. The IC supports single or bipolar supplies.
  2. You may also define ground as Vdd/2 on a single supply by buffering precision equal R's. Then use a Diff Voltage for 0V using Vbias Ref IN.
  3. LDO' are only followers so P and N type are necessary
  4. No you can't use the same LDO's and this complexity may be unnecessary, depending on tolerances for 0.00V
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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