Is possible to ADC read the VREFP in LPC824?

[tiagofernandes]

Hello,

Is possible the ADC read the value presented in the VREFP or the microcontroller know this value using a LPC824 microcontroller? If yes, is possible to add a example or an explanation, because I don't find nothing in the datasheet.

Best Regards,
Tiago

[sirurx]

Hi Tiago,

It is more fundamental question - you need reference what is not dependent on supply voltage.

Usually you would use brown-out mechanism or external zener diode or something similar to check if supply voltage is ok.

BR,

Ergo

[tiagofernandes]

Hello Ergo,

Thanks for the answer. Yes I know that usally external zener diode to verify the voltage is OK. This question has, if voltage has to low, but the micro can continue working, the difference from the initial voltage as change and then the values to the ADC conversion will change too. To the micro automatically adjust the values could have some mechanism to "read" the input/reference voltage.

Best Regards,

Tiago

[lpcxpert · Accepted solution]

The value of VREFP when it is read by the ADC is always 0x0FFF, which is the max value.

Regardless of the absolute value in Volt on the VREFP signal, VREFP is always the max value for all ADC conversions.

Bottom-line: You cannot read the absolute value of VREFP in Volt.

[tiagofernandes]

Hello,

Thanks for answering to my question. If the input voltage in VREFP is equal to VREFN, the value will be always 0x0FFF? I understood what you tell, but I'm trying to know if is possible to know the ADC is powered.

Best Regards,

Tiago

[lpcxpert]

Hi Tiago,

the ADC does not work if there is no voltage on VREFP. You have to test what the conversion result under this condition may be.

Regards,

Peter

[tiagofernandes]

Hello Peter,

Thanks for the answer. I know that the ADC not work if there is no power in the VREFP, but I made this question because, the LPC82x can work with voltages <3.3V and >1.8V. When is supply came from a battery, the battery voltage will down with the time, so I need to know the voltage in the VREFP (I have connect the VREFP to the VCC(3.3V)).

Best Regards,

Tiago