Part Number: TMS320F28069 Tool/software: Code Composer Studio I have been developing data acquisition hardware based on 28069 MCU and found some issues with 12bit ADC, wondering if someone can explain. My ADC configure: AdcRegs.ADCCTL2.bit.ADCNONOVERLAP = 1; // Enable non-overlap mode AdcRegs.ADCCTL1.bit.INTPULSEPOS = 1; // late interrupt pulse AdcRegs.INTSEL1N2.bit.INT1E = 1; // Enabled ADCINT1 AdcRegs.INTSEL1N2.bit.INT1CONT = 1; // Enable ADCINT1 Continuous mode AdcRegs.INTSEL1N2.bit.INT2E = 1; // Enabled ADCINT2 AdcRegs.INTSEL1N2.bit.INT2CONT = 1; // Enable ADCINT2 Continuous mode AdcRegs.INTSEL1N2.bit.INT1SEL = 0; // setup EOC0 to trigger ADCINT1 to fire AdcRegs.INTSEL1N2.bit.INT2SEL = 1; // setup EOC1 to trigger ADCINT2 to fire AdcRegs.ADCSOC0CTL.bit.CHSEL = 0; // set SOC0 channel select to ADCINA0 AdcRegs.ADCSOC1CTL.bit.CHSEL = 8; // set SOC1 channel select to ADCINB0 AdcRegs.ADCSOC0CTL.bit.TRIGSEL = 0; // set SOC0 start trigger on cputimer1,but initially off AdcRegs.ADCSOC1CTL.bit.TRIGSEL = 0; // set SOC1 start trigger on cputimer1,but initially off AdcRegs.ADCINTSOCSEL1.all = 0x0; AdcRegs.ADCINTSOCSEL2.all = 0x0; AdcRegs.ADCSOC0CTL.bit.ACQPS = 8; // set SOC0 S/H Window to 9 ADC Clock Cycles, AdcRegs.ADCSOC1CTL.bit.ACQPS = 8; 1. different SR gives slightly different ADC result. Giving input at about half Vref, I had a sweep of different SR (100KHz to 3MHz). Some SR gives 3-4 LSB difference against normal 12bit code. Not sure if it is normal? 2. At higher SR ( such as 1.5MHz), I have to use OVERLAP for both channel on, in this case, channel A and B will affect each other. e.g. If I turn on or off one of the channel, ADC result of the other channel can be noticeable higher or lower. So I have to use NONOVERLAP, and ACQPS >7 to eliminate this, resulting lower SR. 3. When I am measuring small signal, I can observe at least 3-4LSB of ADC result is not correct. for example, I supply ADCIN with 50mV 1KHz sine signal centering at 1024mV(Vref=2048mV), whenever the signal cross the mid-value which is about 1024mV, the result waveform is like oscillating a bit (at least 3-4 LSB) rather than smooth waveform and then becomes normal. 4. Setting ACQPS=6 or 7 is not working for SR = 2MHz, the result waveform becomes rather bad, huge distortion. but it is OK for other sample rate, even for higher SR=3MHz. So I set ACQPS=8, and it is fine. Are these known issues with the ADC? or is it caused by maybe bad layout? Or my ADC configure is not correct? Very appreciate if someone can give me some clue.
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