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K22: Calibrating ADC with VDDA = 3.3V, VREFH = 2.5V?

Question asked by Troels Østeraa on Sep 8, 2017
Latest reply on Sep 11, 2017 by max Kessler

Hi there,

 

I have found one discussion regarding using dual 3.3V supplies for VDDA and VREFH and disussing whether or not this was a good idea. I have searched, but couldn't find anything on this subject.

 

My device: MK22FN256VLL12

 

I need to use a 2.5V external, high precision voltage reference for the ADC, so that is connected at the VREFH pin.

However, I also want to ensure the the performance/gain/offset of the ADC is as good as possible, so I am implementing the calibration procedure as also described in AN3949.

 

AN3949 states that VREFH and VDDA should be above 3V. The Reference manual for my device states that VREFH = VDDA. I meet neither of those requirements.

 

- What would your recommendation be in such a case?

- Can I just multiply the sum of CLP and CLM registers by 3.3/2.5 or something?

 

I'd rather not spend money on a DC switch that can be controlled by a GPIO, if this can be avoided.

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