ESP32 Forum

The Vref for ADC conversion is noted briefly in the docs as 1.8v but there seems to be little mention of how to get the Vref signal off of the chip or how to get an external Vref into the chip in order to set the driving voltage to external sources in order to get accurate analog measurements.

I've searched the Technical Reference Manual and there's very little info on handling or setting Vref.

Most chips with an ADC either make the Vref available externally or allow an external Vref to be supplied. I can't find this capability on the ESP32-S3.

Any hints? Is it hiding in the IO_MUX docs somewhere? I can use an external 1.8v reference to drive the sources, but it will NOT be exactly the same as the Vref being used by the SAR ADCs. I'd rather avoid the error if possible.

I can't complete the hardware design without this information obviously. I'm new to ESP32 but not MCU's and their peripherals in general.

Vref for the ADC is around 1.1V but differs per chip; we record how much it differs in the eFuses of each chip. If you use adc calibration, it'll automatically correct for this as well as other ADC non-linearities.

Actually i met with an same thing, here what i find even after you use the calibration it doesn't give you the proper voltage output, In microcontrollers max ADC offset count is 5 but in ESP32s3 it leads more counts, in my research i found out using ADC_Atteun_DB_0 is better in in terms of millivolt it differs 2mV otherwise not better once again u need to take five or 10 samples from it.

if any one found the option for ADC accurate results, update to me also....

Can the reference voltage be output to a pin somehow? Then I could buffer it and carry it to the points needed to get the full ADC measurement range and not have to attempt to match it externally ... which will always be off.

Generally it can (although it varies between chips wrt if the code for that is implemented), but as far as I understand it uses the ADC mux for this so you cannot both output the voltage as well as take an ADC reading.