topic Re: RT1170 ADC reference voltages in i.MX RT Crossover MCUs

RT1170 ADC reference voltages

raddeh — Wed, 08 Jun 2022 13:51:13 GMT

The ADC on the RT1170 series processor is documented to have 3 selectable reference voltages. Those are 1.8V, 3.3V and an external V_REFH. A reference source can be selected via the REFSEL field in the CFG register of the ADC.

What I'm unable to find is which setting in this field corresponds to which reference voltage. The options for this field are documented as "See the chip configuration information on the voltage reference options specific to this packaged device.", but I can't find this information anywhere?

Which source is selected when setting the filed to 0b00, which when setting it to 0b01 and which when setting it to 0b10?

Best regards

Re: RT1170 ADC reference voltages

raddeh — Mon, 13 Jun 2022 09:33:45 GMT

Push-to-top. I haven't received any answer to this question yet.

Re: RT1170 ADC reference voltages

CarlosGarabito — Fri, 17 Jun 2022 02:58:52 GMT

Hi @raddeh , the ADC is documented in the reference manual,

The reference voltage is 1.8V, As shown below

So if we continue reading, the ADC Reference voltage design we find

So, if you have 1.8v, then ADC_VREFH = 1.8V *（64/30） = 3.84V

Re: RT1170 ADC reference voltages

gcary — Fri, 24 Jun 2022 18:31:20 GMT

Thank you Carlos for that answer. Is there an error associated with using the 30/64 scaling option? How is it implemented inside of the RT1170?

Edit: I thought the question I asked was related and short enough to add to this thread, but I've decided I have more questions that are related and it would be best to open a new one. Here is another thread on this topic that is worth reading:

https://community.nxp.com/t5/i-MX-RT/MIMXRT1176-LPADC-voltage-reference-scaling/m-p/1386125

I don't think 1.8V is best to use with CSCALE because the result exceeds the recommended supply voltage. VREFH should be limited to 1.54V.

Re: RT1170 ADC reference voltages

CarlosGarabito — Sat, 25 Jun 2022 15:02:38 GMT

Hi @gcary you need to open a new issue to see your case, because this is close now

Best regards

Re: RT1170 ADC reference voltages

gcary — Sat, 25 Jun 2022 17:20:01 GMT

Thanks Carlos. I already did. Here is the link:

https://community.nxp.com/t5/i-MX-RT/RT1170-ADC-Input-Voltage/m-p/1479993