CCS/TMS320F28035: TMS320F28035 ADC values can not reach to 4095

There is some amount of gain error that is listed in the DS, but I believe the max for an external reference is 40LSB, so this doesn't explain the error you observe(4095-3842 = 253).

Can you confirm the voltage on the VDDA supply?  If this is lower than your VREF/ADCIN this could cause conversion issues above that value.

Also can you comment on the VREFLO voltage as well.

Best,

Matthew

HI,

Matthew ,

pin20 = Vdda = 3.255V = pin19 = VREFH0,

VREFL0 = GND = 0V

ADCVIN = 3.255V,result = 3920, erro is (4095-3920 = 175).

ADCVIN = GND,result = 0~5

I set ：

AdcRegs.ADCCTL1.bit.ADCREFSEL = 1 or 0 is the same result,why?

thanks!

The internal reference is calibrated to give a full scale range of 0-3.3V; when you make ADCREFSEL = 1 the ADC should use the VREFHI pin voltage to set the high limit, to in this case it should re-range to 0-3.255V

Have you made sure to run the ADC calibration routine(either from the Scripts in CCS or in your code), this will load the ADC calibration fields with the correct values to achieve the DS specs.

You can check the ADCREFSEL and ADCOFFSETTRIM registers for non-zero values to confirm this.

Best,

Matthew