How to test the ADC input is not connected

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How to test the ADC input is not connected

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zhaoyanling
Contributor III

Dear expert,

I use S32K144, The ADC result is gotten with DMA interrupt. There is a problem about ADC, Could you help me ?

I found, When I disconnected the ADC1_SE0, which means the ADC annalog input is nothing, but I still can get the DMA interrupt, and the Digital output is nearly 5V. By the way, Vref_h = 5V, Vref_L = grand.

1.How can I know the ADC input is open circuit?

2.When a pin is not used as GPIO, the pull down can not be set. 

Thank you very much!

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zhaoyanling
Contributor III

Hi, Daniel,

Do you mean, If the pin ADC1_Se0 is enabled pull-down, when the PTA2 pin (in ADC1_SE0 function) is not connected,then the digital output is  0 voltage?

Thank you very much for your reply!

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danielmartynek
NXP TechSupport
NXP TechSupport

Hi zhaoyanling@bhap.com.cn,

Yes, that's what I mean.

Or do you observe something else?

Regards,

Daniel

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danielmartynek
NXP TechSupport
NXP TechSupport

Hello zhaoyanling@bhap.com.cn,

1. When the PTA2 pin (in ADC1_SE0 function) is not connected to any circuit, the pin is floating, and the state of the pin cannot be defined.
2. But the internal pull-down can be enabled in every function of the PTA2 pin, including ADC1_SE0.

Regards,

Daniel

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