TAS2781EVM: How to use TAS2781"PWM_CTRL" function work

Simon Yuh

Other Parts Discussed in Thread: TAS2781EVM

Hi Sir

We would like to use PWM_CTRL function to control external boost on EVB. After we initialized TAS2781EVM and typed in below command.

w 70 00 00 #Page 0x00
w 70 7A 20 #PWR CTRL

w 70 00 00 #Page 0x00
w 70 6A 05 #LVS_RTH

Then adjusted input from 0dB to -40dB.

But we didn't see the signal with a duty cycle on the PWM_CTRL pin as written in the datasheet.

Even though we remove R6 pull high 1K register.

Could you help to figure out the operation method?

-----------------------------------------------------------datasheet below-------------------------------------------------------------------------------------------

When enabled, the controller generates at PWM_CTRL pin a signal with a duty cycle proportional to the peak voltage on the speaker. Using an external RC filter the signal is converted to an analog voltage and can be used to control boost converters with feedback input.
The figure below shows how the PWM_CTRL pin can be connected to the external boost control RC network.

11 months ago

0 Arthur Brown 11 months ago

TI__Mastermind 18245 points

Hi Simon,

I recommend that you first use the PPC3 GUI to configure the Class-H boost.

there is an app note which describes the functionality and configuration of this feature. https://www.ti.com/lit/an/sloa326/sloa326.pdf

Regards,
Arthur

0 Simon Yuh 11 months ago in reply to Arthur Brown

Prodigy 100 points

Hi Sir

I followed the steps from the link you provided as shown in the picture below, but I don't see any variety at PVDDH, it always keeps 12V.

What else step did I ignore?

0 Arthur Brown 11 months ago in reply to Simon Yuh

TI__Mastermind 18245 points

Hi Simon,

Can you please share a clear image of the EVM? I would like to check that the jumpers are correctly configured.

Also, by default the PWM_CTRL pin is open drain so removing R6 could be the reason that PVDD is stuck at 12V.

Regards,
Arthur

0 Simon Yuh 11 months ago in reply to Arthur Brown

Prodigy 100 points

Hi Sir

Even if I stick R6 back to the EVM, I still don't see the PVDDH go high/low after input trim(-40dB to 0dB).

0 Simon Yuh 11 months ago in reply to Simon Yuh

Prodigy 100 points

Hi Sir

Do you have any suggestion?

0 Arthur Brown 11 months ago in reply to Simon Yuh

TI__Mastermind 18245 points

Hi Simon,

I believe that R6 is required since the output is open drain, have you tested with it inserted?

Regards,
Arthur

0 Simon Yuh 11 months ago in reply to Arthur Brown

Prodigy 100 points

Hi Sir

Yes, per previous discussion, I have installed R6 back to the EVM, I still don't see the PVDDH go high/low after input trim(-40dB to 0dB).

0 Arthur Brown 11 months ago in reply to Simon Yuh

TI__Mastermind 18245 points

Hi Simon,

I will need to set this up in the lab. I can share my ppc3 file and image of the board setup to you. I can test this tomorrow.

Regards,

Arthur

0 Simon Yuh 11 months ago in reply to Arthur Brown

Prodigy 100 points

Hi Sir

Thanks for your help, I appreciate it.

0 Arthur Brown 11 months ago in reply to Simon Yuh

TI__Mastermind 18245 points

Hi Simon,

Attached is the 2781 ppc3 file with the Class-H boost enabled, I verified it is working on my EVM.

Also including an image of my jumper settings

Class-H-enabled.ppc3

Regards,
Arthur

0 Arthur Brown 11 months ago in reply to Simon Yuh

TI__Mastermind 18245 points

Hi Simon.

I attempted to attach the image, but E2E is having some issue, I checked your image of the jumpers and they are the same. can you test the file and let me know if you have success?

Regards,
Arthur

0 Simon Yuh 11 months ago in reply to Arthur Brown

Prodigy 100 points

Hi Sir
I implement your file "Class-H-enabled.ppc3" into the PPC3, but didn't see the PVDDH go high/low after input trim(-40dB to 0dB).

The following is my step.
1. import "Class-H-enabled.ppc3" in to PPC3 interface as picture.
2. measured PVDDH at J10 & J7.
3. adjected input level from -40 dB to 0dB and watch the PVDDH voltage if it can change from 5V to 12V.
But the result I only saw PVDD= 11.61V / 12.56V change between input level -15dB and -14dB.
Can you show me the step your operation?

+1 Arthur Brown 11 months ago in reply to Simon Yuh

TI__Mastermind 18245 points

Hi Simon,

I just checked and it appears when the .ppc3 file is imported it is not retaining the "Device Control" settings which have the external Class-H settings.

Can you please go to the "Device Control" panel, then scroll down to "Class-H" and turn the feature on? this should enable the feature.

Regards,

Arthur

0 Simon Yuh 11 months ago in reply to Arthur Brown

Prodigy 100 points

Hi Sir

Thanks for your help, I can see the result.

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TAS2781EVM: How to use TAS2781"PWM_CTRL" function work