working temperature impact on ADC

[Ben]

Hello

I noticed that the ADC readout changed while working temperature is changed.

Anyone knows something about it?

Ben

[xiangjun_rong]

Hi, Ben,

Can you tell me the part number you are using? do you use Sar ADC(16 bits ADC) or Cyclic ADC(12 bits)? Do you use internal voltage reference or external voltage reference? how much is the temperature effect?

BR

Xiangjun rong

[Ben]

Hi, thank you for responding.

I needed an external bus in the project, so I didn't have many options. I used the 56F8367.

Normally, most indoor projects works in a stable temperature, but this is an outdoor application.

I am using 12bit A/D with a separate quiet analog voltage power supply .

Temperature change cause a readout drift of 3 bits, and I had to add an external temperature sensor with digital output and to add a compensation algorithm. This is very strange. ADC should be stable.

[xiangjun_rong]

Hi, Ben,

I have checked the data sheet of the 12 bits ADC of MC56F8367, we do not do the test for the temperature impact on the ADC result accuracy, i am sorry.

Regarding you case, if you connect the ananlog GND to ADC analog channel pad, what is the result?

If the temperature sensor has large output impedance, I suggest you connect a buffer with analog amplifier to  reduce the impedance(connect the temperature output signal to non-inverse pin of AMP, connect the inverse pin of AMP to output pin of AMP).

I suggest you use external voltage reference for the VREFH pin of ADC.

I suggest you use independent power supply for the VDDA pin.

Hope it can help you

BR

Xiangjun Rong

[Ben]

Hi

Thank you for the efforts. As I had to solve the customer needs fast, I think that the solution I did was the fastest and low cost one - adding digital temperature sensor to the circuit, and correlate the analog rearing according to the temperature.

It is very strange that temperature  has such influence  on ADC, usually ADC chips are more stable. Therefore I wondered if NXP / Freescale had any AN on this issue. From your answer I understand you don't have it. I will have to bring this issue in consideration on the next DSC project, and will check your suggestions.

Best regards,

Ben