LAUNCHXL-CC26X2R1: The voltage value will drop when using DAC_setCode

Kevin Qiu

Intellectual 1530 points

Part Number: LAUNCHXL-CC26X2R1

Hi Team,

SDK:simplelink_cc13xx_cc26xx_sdk_5_30_00_56

The customer finds that the voltage drops by118mV when outputCode is set from 127 to 128 when using the DAC_setCode():

Then the customer tested the routine dacoutputbuffer and found that there was also a reverse jump in the sine wave:

Could you help to check it?

Regards,

Kevin

over 4 years ago

0 Clément over 4 years ago

TI__Guru** 101490 points

Hi Kevin,

Thank you for reporting this issue. Could you please provide the code used to produce this sinus? It will help us to reproduce.

I have asked an expert to comment.

Please bear with us.

Best regards,

0 Kevin Qiu over 4 years ago in reply to Clément

TI__Intellectual 1530 points

The sine wave codes are just the dacoutputbuffer example that isn't modified.

0 AndresM over 4 years ago in reply to Clément

TI__Expert 3886 points

Hi Kevin,

I'm guessing that the customer is using the example as it is (i.e., default configuration). Am I correct?

I'll check the settings for the example and see if there is anything that can be done to improve the output. Bu it's worth mentioning that the main use of the DAC peripheral is as a reference DAC. So the type of output that you see in the example is basically to show how far you can push the peripheral, and how the different APIs can be used depending on the application.

BR,
Andres

0 Kevin Qiu over 4 years ago in reply to AndresM

TI__Intellectual 1530 points

AndresM said:
I'm guessing that the customer is using the example as it is (i.e., default configuration). Am I correct?

yes.

The customer wants to know why there is a voltage jump phenomenon.

0 AndresM over 4 years ago in reply to Kevin Qiu

TI__Expert 3886 points

Hi Kevin,

I have reproduced the issue the customer is seeing. I need to determine whether or not there is an issue with the driver. I'll get back to you once I know more.

BR,
Andres

0 Kevin Qiu over 4 years ago in reply to AndresM

TI__Intellectual 1530 points

Thank you. If there are any new discoveries, please let me know.

+1 AndresM over 4 years ago in reply to Kevin Qiu

TI__Expert 3886 points

Hi Kevin,

After some testing and debugging I identified what is causing the issue, and how to fix it.

First, this is how it looks when the fix has not been applied:

The issue is caused when setting the sample clock base frequency in the DAC_enable() API. It can be solved by modifying line 265 in DACCC26X2.c.

Currently the line is:

AUXDACSetSampleClock(DAC_CLOCK_FREQ_24MHZ);

It should be modified to:

AUXDACSetSampleClock(0x01);

When this is done, the output will look like this:

In order to integrate these changes, it is important to follow these steps in the project:

Add the file C:\ti\simplelink_cc13xx_cc26xx_sdk_5_30_00_56\source\ti\drivers\dac\DACC26X2.c to the project. When asked about how the file should be imported, select “Copy files”.
Once the file is part of the project, open it and modify the line of code that I mentioned before.
Build the project.
Test.

I’ll make sure to file a ticket so that the bug is fixed for the next SDK version.

Let me know if you have any problems implementing these changes.

BR,
Andres

0 Kevin Qiu over 4 years ago in reply to AndresM

TI__Intellectual 1530 points

The customer also found that after the reference voltage was changed to ADCREF, the DAC could not output voltage.

Could you help to check this?

+1 AndresM over 4 years ago in reply to Kevin Qiu

TI__Expert 3886 points

Hi Kevin,

This is something that I do not see. When changing the reference to ADCREF, the only thing that I see different is that the output voltage range changes (which is expected).

BR,
Andres

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LAUNCHXL-CC26X2R1: The voltage value will drop when using DAC_setCode