RT1040 ADC issues

[Xiao_Liu]

Follow IMXRT1040RM  ， disable GPIO keeper for ADC input signal。

if ADC input gpio is NC，ADC read value is abnormal，the NC input pin is 0V measured by multimeter.

we have another ADC channel which is connected to an NTC thermal sensor. the ADC read value is ok.

When i set ADC GPIO pin config as default( 

IOMUXC_SetPinConfig(ADC_PIN, 0x10B0U)), this is set keeper enable as default, the ADC read value of input channel which is NC is nearly zero. it's work this time.

So, Should i disable Keeper function of GPIO for ADC input signal?

[Xiao_Liu]

Hi,May:

       The ADC is designed to be floated if module is not connected. the module is Optional. 

       Follow "ECKMIMXRT1040_ADC_12B1MSPS_SAR_POLLING" , the ADC input pin of GPIO_AD_B1_04 is set as keeper function  disable.

       the NC ADC input pin is measured as 0V,  but ADC read value is 0.6 or 0.7V if keeper disable.

       ADC read value is nearly 0V  if keeper enable as default. by this way we can use ADC read value as module detection

       So, what the side effect when keeper is enabled.

       What should i do to read ADC input pin which is NC as we need auto detect of the optional module?

[mayliu1]

Hi @Xiao_Liu ,

Thanks for your updated information.

Enabling the keeper on an ADC pin is not recommended. The keeper holds the last state, which can cause incorrect ADC readings and makes module detection unreliable.

For a stable and accurate result, we recommend adding an external resistor to set a clear default level when ADC  is not connected.

Best Regards

MayLiu

[Xiao_Liu]

Hi,May
got it. we will use external pull up when ADC is not connected.
thanks for your help.

[mayliu1]

Hi @Xiao_Liu ,

Thanks for your updated information.

If this post answers your question, please click the "Accept As Solution" button. Thank you!

Best Regards

MayLiu

[mayliu1]

Hi @Xiao_Liu ,

Thank you so much for your interest in our products and for using our community.

Regarding your question,

Yes. For ADC input pins, the keeper function should be disabled.

Please refer to NXP SDK demo PIN setting.

Please note that an ADC channel should not be left floating; if the pin is NC, the conversion result is undefined.
Enabling the keeper may make the reading look stable, but it is not a reliable or recommended solution.

Wish it helps you

Best Regards

MayLiu