NRF52832 SAADC Intermittent Failure

RE: NRF52832 SAADC Intermittent Failure

Kenneth — Tue, 25 Apr 2023 21:02:17 GMT

[quote user=""]The data read by the SAADC almost looks like a capacitor charging up, which is not the signal it is receiving. [/quote]

I know I have seen something simliar when the source have been very high impedance, but I don't expect that is the case here.

A list of known issues are found here:
https://infocenter.nordicsemi.com/topic/errata_nRF52832_Rev3/ERR/nRF52832/Rev3/latest/err_832_new.html

This chip have been in production for quite some time, so I don't expect there are any unknown issues at this time.

Kenneth

RE: NRF52832 SAADC Intermittent Failure

_Scott_ — Tue, 25 Apr 2023 20:56:52 GMT

I don't think it's possible for the SAADC input voltage to have been exceeded. The channel in question is fed by a op-amp powered by VDD, so should not have exceeded VDD. VDD is provided as the output of a voltage regulator. The NRF52 is powered by a separate voltage regulator, but both output the same voltage, and were within 0.007v of each other when I checked.

The unit was in a plastic case, so the only other thing I could think of is a static shock during assembly. Not sure if a static shock could cause damage that presents itself as intermittent failure, but I'm just trying to make sure there isn't some other issue with the SAADC we need to be aware of.

RE: NRF52832 SAADC Intermittent Failure

Kenneth — Tue, 25 Apr 2023 18:49:51 GMT

Sounds to me that the input have been damaged somehow, considering only one chip and one input show the issue. Is it possible that the input at any time might have exceeded <GND-0.3V or >VDD+0.3V?

Kenneth

RE: NRF52832 SAADC Intermittent Failure

_Scott_ — Tue, 25 Apr 2023 16:17:50 GMT

There is no circuitry between where I connected an oscilloscope and the nrf52 chip. The SAADC is reading the value from an amplifier circuit, and the oscilloscope verified the amplifier circuit is working as expected. I scoped the output of the amplifier on the trace that connects directly to the nrf52 chip. This is what led me to believe something is going on with the SAADC channel. Ground should be connected properly, all other SAADC channels used read the correct values, which means ground and VDD are as expected. Yes we are currently only seeing it on a single device. The device was in use for some months. At some point the failure was highly intermittent, device could be used for days at a time without issue. Now the device is is seeing incorrect SAADC values ~90% of the time it is booted up, but still occasionally works as expected.

RE: NRF52832 SAADC Intermittent Failure

Kenneth — Wed, 19 Apr 2023 14:57:23 GMT

Hello,

I don't see any obvious reason for this no.Is there some circuitry between the input line and the physical pin on the chip thay may cause the pin to have a higher level than what is on the input level? Do you see this only one product in specific? I assume ground is connected properly?

Kenneth