ADC single mode resolution

[LuBe_4654241]

Hi,

I am using theADC in single mode, but I noticed that is avaible the conversion in unsigned mode, why ?

All ADCs have the unsigned conversion.

Best Regards

LuBe

[LuBe_4654241]

Hi,

another problem that I am seeing is the VRef select in ADC (Demo board CY8CKIT-041-41XX):  If I use VDDA as VRef the conversion value is 2047 on channel 1 connected to 3V3, but If I use external VRef that I connected to 3V3 the value is about 1605. Do you know where is the problem ?

Best regards

Luca Bernabei

[Vasanth]

Hi Luca,

Regarding your first question, the SAR ADC in psoc by architecture is a differential ADC. But if you have connected the negative input of the ADC to VSS, the range of the ADC is half, as the other half of the ADC which is below VSS is not available for conversion. In such a case you have to change "Single Ended Negative input to Vref to achieve signed and unsigned results.

Regarding your second question, first I would request you to confirm whether both the voltages are equal using a multimeter(VDDA, external Vref and the input voltage). If all voltages are proper we will dig deep into this.

Best Regards,
Vasanth 

[LuBe_4654241]

Hi Vasanth,

for question 1 okay.

About the question 2, I have verified the voltage of VDDA, it is  1V9, whilst the external VRef is 3V3 and input is 3V3. 

Best regards

LuBe

[Vasanth]

Hi Lube,

That is the reason for the wrong results. Did you find the reason why the VDDA is 1.9V at your end ? Did you check whether the device is powered properly?

Best Regards,
Vasanth

[LuBe_4654241]

Hi Vasanth,

the voltage on VDDA is correct, because there are the deep switch on board:

The problem is when I use external Vref connected to 3V3 and channel 0 connected to 3V3, in this condition the value of ADC is about 1605. The correct value would be 2047.

Best regards

LuBe

[LuBe_4654241 · Accepted solution]

Hi Vasanth,

the problem was that the VDDD and VDDA were 1V9, whilst VRef 3V3.

Problem solved.

Thanks

LuBe