TMS320F28P650DK: ADC Fluctuation

Reza Rezaii

Part Number: TMS320F28P650DK
Other Parts Discussed in Thread: SYSCONFIG, TMDSCNCD28P65X

Hi,

I'm facing an issue while testing the ADCB module on TMS320f28p65. Here's my setup:

ADC Configuration: Set to 16-bit resolution using SysConfig
Trigger Source: EPWM18
Data Transfer: Using DMA
Input Signal: Constant DC voltage with no observable noise
REF Voltage: 2.5V external voltage

Despite the input voltage of ADC pin and REF voltage being stable, I'm seeing a fluctuation of about 300 counts in the ADC result. Would you please help me for this problem.

8 months ago

0 Reza Rezaii 8 months ago

Prodigy 90 points

This is a GIF for the ADC results.

0 Stevan Duraskovic 8 months ago in reply to Reza Rezaii

TI__Expert 7170 points

Hello Reza,

Could you please go to Sysconfig and show me your ASYSCTL configuration? You would need to select voltage reference in that tab.

0 Reza Rezaii 8 months ago in reply to Stevan Duraskovic

Prodigy 90 points

Hi Stevan,
I have selected as external.

0 Stevan Duraskovic 8 months ago in reply to Reza Rezaii

TI__Expert 7170 points

Reza,

Could you check generated files, board.c file and show me the generated lines of code?

0 Reza Rezaii 8 months ago in reply to Stevan Duraskovic

Prodigy 90 points

This is the generated code in board.c

0 Stevan Duraskovic 8 months ago in reply to Reza Rezaii

TI__Expert 7170 points

Reza,

Do you intend to use a single-channel ADC or differential ADC in your application? As it is now you have selected differential (16-bit mode).

0 Reza Rezaii 8 months ago in reply to Stevan Duraskovic

Prodigy 90 points

I am using a single-ended ADC. Where have I selected differential (16-bit mode) ADC channel?

0 Stevan Duraskovic 8 months ago in reply to Reza Rezaii

TI__Expert 7170 points

Reza,

In your Syscfg please select 12-bit instead of 16-bit at this place.

Hope this fixes the issue.

0 Reza Rezaii 8 months ago in reply to Stevan Duraskovic

Prodigy 90 points

Does this 16-bit work only for differential ADC?

I think we select the differential or single-ended is in the SOC setting:

0 Stevan Duraskovic 8 months ago in reply to Reza Rezaii

TI__Expert 7170 points

Hello,

You're correct, it seems that you have applied correct configuration for single-ended channel. Do you have the same issues when you use internal VREFHI?

0 Reza Rezaii 8 months ago in reply to Stevan Duraskovic

Prodigy 90 points

Yes, I have. Even with internal VREFHI we have this issue. Even with TI example, we have this issue.
I should mention that I am using TMDSCNCD28P65X Control card.

0 Stevan Duraskovic 7 months ago in reply to Reza Rezaii

TI__Expert 7170 points

Hello Reza,

I apologize for the delay in reply. Could you let me know which revision of TMDSCNCD28P65X Control card are you using, please? It should say on the silkscreen bottom right corner.

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TMS320F28P650DK: ADC Fluctuation