ADC missing values

Hi Mike,

AdcRegs.ADCSOC11CTL.bit.ACQPS = 025;

If I increase to

AdcRegs.ADCSOC11CTL.bit.ACQPS = 0x3f;

the jump is from 3487 to 3492. Why?

ACQPS is what determines the sample and hold window size. More the size better the results. But one should also consider the time taken :

About jumping values, such a phenomenon tends to happen and is normal.

Regards,

Gautam

About jumping values, such a phenomenon tends to happen and is normal.

I have used many other processor and expect 1-2 bit jumps but not suggest big jumps.

I have used many other processor and expect 1-2 bit jumps but not suggest big jumps.

What are you using as your ADC input? DC supply?

I am supplying the PCB with 5V from a bench supply. There is a 3V3 regulator on the PCB. The ADC input is generated by a potentiometer (10 turn pot) 

The ADC input is generated by a potentiometer (10 turn pot)

Is this a custom board or dev board?

Custom board

Custom board

Are you using any RC filters at ADC inputs? or directly feeding the signal?

Using RC filter R = 3k3, C = 4n7

I run a test with the same analogue input voltage for all 3 tests.

Test 1 ACQPS=63.CLKDIV2EN=1.CLKDIV4EN=1

Test 2 ACQPS=25.CLKDIV2EN=1.CLKDIV4EN=1

Test 3 ACQPS=25.CLKDIV2EN=0.CLKDIV4EN=0

So reducing the sample window size with CLKDIV2EN=1.CLKDIV4EN=1 causes the results to go up. Reducing the sample window size by changing CLKDIV2EN and CLKDIV4EN to 0 give very jump lower results.

This is a 90HMz processor. Is there a maximum limit the ADC section can be clocked at? 

Is there a maximum limit the ADC section can be clocked at?

Refer this link for more info:

http://e2e.ti.com/support/microcontrollers/c2000/f/171/t/96941.aspx

Regards,

Gautam