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?
  • 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
    Commented 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\$ Commented 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
    Commented 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
    Commented Aug 26, 2021 at 14:16

1 Answer 1

  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

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