SDADC results are 50% of the actual value?

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SDADC results are 50% of the actual value?

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ignatiusmichael
Contributor II

Hi,

We are currently configuring SDADC to run in single ended mode, When we supply 5v from the pot on the evaluation board we are getting a value of around 32000(0x7E9C) which as we reduce the voltage from the pot the value decreases and at 0v give a value of 7(approx 0).

It is my understanding that since the SDADC is 16 bit the result at 5V should be 0xFFFF which is not happening 

In order to verify the working of my code i then flashed the Example project - Example MPC5777C-SDADC_simple GHS614.

In this project at 5v the value is 16396(0x4002) same as ours but then as we reduce the pot value the value first decreases to 0 at around 2.6V then rolls over to 65535 at 2.5v(approx) and at 0V shows a value of 49361(0xC0CA).

This behavior was not happening in my code.

Why is this happening and how do i fix it?

(Voltages on pot have been verified with a multi-meter)

We are using MPC5777C with the Evaluation Board pot is connected to PO15

Any help is appreciated

Regards,

Michael Jihan

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davidtosenovjan
NXP TechSupport
NXP TechSupport

Hi, it is because of negative input terminal is with the configuration used in the example biased at Vref/2. You can change the configuration according to your need.

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