%XVBAT Accuracy

RE: %XVBAT Accuracy

Andreas — Fri, 15 Feb 2019 13:00:44 GMT

Hi,

Correction: Using the %XVBAT command, measuring battery voltage up to 5.5V is supported.

Max input on GPIOs is VDD_GPIO, meaning upper voltage is limited to this when using the SAADC. Currently the documentation is not correct with regards to this, and this is to be fixed. Note that for engineering revisions, errata 16 applies.

Best regards,

Andreas

RE: %XVBAT Accuracy

awneil — Thu, 14 Feb 2019 22:45:58 GMT

[quote userid="77324" url="~/f/nordic-q-a/43730/xvbat-accuracy/171235"]It doesn't quite answer my question.[/quote]

True.

The point is that the whole idea of using battery voltage to gauge remaining capacity is deeply flawed - so you may be better pursuing a better approach rather than messing about with trying to perfect the voltage reading ...

RE: %XVBAT Accuracy

ProfHindsight — Thu, 14 Feb 2019 20:13:22 GMT

Thank you for the quick response awneil!

It doesn't quite answer my question. The nRF91 is able to take an input voltage of 3.0 - 5.5 on the VDD pin. The LiPo battery will have a range of roughly 3.3 - 4.5V.

The AT command in question can be found under section 4.23 of nrf91_at_commands_v0.7

The full-scale resolution note of 3.6V is found in section 6.12.8 of nRF9160_OPS_v0.7.1

One question is whether VDD as referenced by the SAADC is VDD, VDD_GPIO, or some other internal regulator on the nRF91.

We currently have the STC3117 in the design but testing it has showed it to be not that accurate in current-voltage mode and the voltage mode seems to measure the voltage and compare against a lookup table. It's possible it does more calculations under the hood - we would include both methods in the design and run a comparison.

Thanks!

RE: %XVBAT Accuracy

awneil — Thu, 14 Feb 2019 19:54:32 GMT

[quote userid="77324" url="~/f/nordic-q-a/43730/xvbat-accuracy"]measure the LiPo battery voltage to determine battery health[/quote]

See: devzone.nordicsemi.com/.../171088