TPA6304-Q1: residual noise caused by power reverse noise

Hello, 

     Thanks for your reply, this help us a lot.

    Another question is the back_light IC, part name is LP8864QDCPRQ1, also from TI , so do there have any method to reduce residual noise from back_light side?

Zhiqiang,  I need to move this thread to LP8864QDCPRQ1's product forum.

Hello, Patrick

    As you see above topic, there have power reverse noise go through this red line back to amp when backlight pwm duty is not 100%, I want to know whether have some method to reduce noise in back_light side?

Thanks

Hi Zhiqiang,

I will assign the expert to give you suggestions.

BR

Patrick

Hi, Zhiqiang 

could you pls clarify the requirement from our LP8864 device? I find PVDD is together with an DC/DC then connect to the LP8864.

You want to reduce the input voltage ripple or any other spec?

sorry, I am late in relaying

    LP8864 is connected to DCDC. When the PWM duty cycle of the back_light input is not 100%, there will be a reverse noise transmitted to the audio channel through the DCDC and the VBATpin of the AMP, affecting the audio performance. Is there any way to reduce this reverse noise on the back_light side?

Thanks

Hi Zhiqiang,

Our expert will give you feedback later.

Hi, Zhiqiang

I am not familiar with the whole system, if you have the concern of PWM dimming. You can change the dimming mode to analog dimming by Mode resistor, pls check the details in datasheet.

Hi, Zhiqian，

    analog dimming mode we cannot use , because the analog dimming mode don't satisfied the minimum duty cycle, so do there have other method to reduce this reverse noise?

Hi, Zhiqiang

For PWM dimming, it is easy to see the dimming frequency ripple on the input supply side. Pls try to change the dimming frequency or add the input cap to change the ripple frequency or decrease input ripple level.

Hi, Zhiqian

    Sorry, changing the dimming frequency also doesn't satisfy the minimum duty cycle, so the dimming frequency we are currently use is 305Hz in our design, what is the appropriate capacitance should be added on the input supply side?

Hi, zhiqiang

I go through with your question, if the ripple is from the PVDD. Just try to reduce the ripple at that side, and it is the input of another boost, it is needed to check with that device. If you cannot change the dimming mode, then try to ensure a less impact on input voltage side.