RE: Can I really not use LPCOMP and ADC at the same time?

Anne van Rossum — Wed, 03 Dec 2014 12:28:41 GMT

Extremely useful! Thanks a lot!

RE: Can I really not use LPCOMP and ADC at the same time?

Anne van Rossum — Tue, 02 Dec 2014 15:42:20 GMT

Thanks! It might indeed be that the PSEL MUX is the only thing shared. That would be nice. I personally don't think the LPCOMP is implemented using ADC circuitry, but who knows... Awaiting your experiment! :-)

RE: Can I really not use LPCOMP and ADC at the same time?

Stefan Birnir Sverrisson — Tue, 02 Dec 2014 12:59:08 GMT

As far as I know, the PSEL MUX is shared. I learned this the hard way when I was trying to monitor voltage with LPCOMP on an AIN pin and sampling with the ADC on another AIN pin. I could enable both of them but the ADC output did not make sense and the LPCOMP did not trigger on the right voltage level.

If I am correct that only the PSEL MUX is shared, then you should be able to measure battery voltage with the ADC while monitoring voltage on AIN pin with the LPCOMP. I have not tried this yet.

I will seek confirmation on that only PSEL MUX is shared with ADC and LPCOMP, and update this thread otherwise.

There is a LPCOMP example available on this thread, ADC examples are available on Nordic's Github

Update 3.12.2014 I have done some testing, seems like the MUX is shared and nothing else. In my test code, I have monitored voltage level on AIN4 pin with LPCOMP and sampled on AIN6 with the ADC at the same time. The higher of the two input voltages will be input to both LPCOMP and ADC. For example if I have 0.6V on AIN6 and 1.5V on AIN4, 1.5V will be input to both LPCOMP and ADC. If I however use the ADC only to sample the supply voltage, i.e. not from AIN pin, then both LPCOMP and ADC work fine.

I include my test code below, which in current state seems to work fine with ADC sampling supply voltage and LPCOMP monitoring voltage on AIN4. I have tested it with nRF51 SDK v6.1.0 and the nRF51822 development kit.

ADC_and_LPCOMP_test.zip

Update 4.12.2014 The designer has confirmed that my findings are as expected. Only the PSEL MUX is shared, so it should be safe to use ADC for battery monitoring while using LPCOMP at the same time.