ADC accuracy on first read

[GuillaumeAudirac]

Using i.MXRT1062, the first ADC value is slightly lower than the expectation.

Settings:

• Software Triggering
• 12 bits ADC resolution

The starting sequence (using fsl_adc):

1. ADC_Init()
2. ADC_EnableHardwareTrigger()
3. ADC_DoAutoCalibration()
4. In loop, at key press:
   1. ADC_SetChannelConfig()
   2. Wait for ADC_GetChannelStatusFlags
   3. ADC_GetChannelConversionValue() at key press

Outputs:

• First value read: ~3200
• Following value read: ~3400-3450

Do you have any idea why the first value is not accurate ?

Thanks.

(sample code attached)

[jeremyzhou]

Hi Guillaume Audirac,

Thank you for your interest in NXP Semiconductor products and for the opportunity to serve you.
I've not replicated this phenomenon that you described, during the testing, I run the ADC demo to sample the Gnd, DCDC_3V3, and DCDC_OUT respectively.

Have a great day,
TIC

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