Issue with Inaccurate ADC Values on S32K3

[NewbieNerd]

Dear S32K3 Team,

I am encountering an issue with inaccurate ADC readings. Here are the details:

• I am using ADC_0 configured with a 14-bit resolution, and the issue is occurring on Channels 40 and 44. Both channels exhibit the same abnormal behavior.
• Specifically, when the input voltage is below 4.7V, the ADC value reads approximately 132xx.
• However, when the input voltage exceeds 4.7V, the ADC value drops to approximately 118xx.
• The hardware correctly reads the voltage, so this appears to be a software configuration issue.

Could you please help identify the root cause of this issue and suggest potential solutions?

Best regards

[NewbieNerd]

You are correct.

When increasing the resistance value on the ADC input voltage, the ADC result decreases, and when lowering the resistance value, the ADC result increases. However, if the voltage exceeds 4.7V, the ADC result becomes lower than the value at 4.7V (showing a value around 3.xV instead).

[davidtosenovjan]

Would you please provide scheme of connection of external ADC circuits?

[davidtosenovjan]

You says, not only that converted value is saturated but even drops down. Is is so?

Please provide details about your measurement, connection and configuration.

[NewbieNerd]

Thank you for your reply!

And no worries about the delayed response due to the New Year's holiday.

I noticed an error in my previous explanation. PTC25's ADC value appears to be functioning normally, meaning that when the input voltage increases or decreases, the ADC value follows accordingly.

The issue lies with the ADC connected to PTD2.

• At 4.6xV, the ADC output is around 132xx.
• At 4.7xV, the ADC output drops to around 113xx.
• When the voltage remains stable, the ADC output does not fluctuate significantly and maintains a consistent trend.

I'll share the ADC circuit diagrams with you.

[davidtosenovjan · Accepted solution]

I don't understand too much what is purpose of D110. Usually current limiting resistor is used instead. It could be source of issues. Also filtering capacitor C105 seems to be too small and it should be placed towards ADC input.

Pay attention to PDF guide I have attached to following thread helping to understand how to choose external ADC components:
https://community.nxp.com/t5/S32K/Smoke-detector-interfacing-with-FS32K146HAT0MLLT/m-p/1773787?profi...

[NewbieNerd]

Thank you for your response.

First of all, I am conducting measurements using PTC25 (ADC_S20) and PTD2 (ADC_S16).
The ADC hardware in use is ADC 0.