TAS5828M: Hybrid Feedback PWM not working as described

Hi Verrill

You want to use Base/Pro 1.0/48K mode with Hybrid PWM feedback?

I am afraid that only Base/Pro 1.0/96K hybrid mode support the Hybrid PWM feedback.

Jesse

Hi Jesse,

I have reconfigured the PPC3 file for  Base/Pro Hybrid 1.0 96k and enabled the Hybrid-Pro feature and set it to GPIO1 using the SRT portion of the tool. I still hear clicking from my boost power stage which can only be eliminated if the connection between the TAS5828M's GPIO1 and the boost feedback terminal is broken,

Do you know what I am doing wrong here or what is mis-configured? It does look like the PVDD rail is influenced by the hybrid feedback pin and goes in the appropriate direction, but I am not able to eliminate the buzzing sound produced by the boost converter when hybrid-pwm is enabled.

The first scope trace shows the SPK_L signal in yellow, the hybrid PWM pin in blue and PVDD in purple while music is playing loudly. The second trace shows the same thing zoomed in. The third trace shows the same signals while music plays at 0 volume and the final trace is after the music has been paused. I have also included a display of the device registers while playing and my full PPC3 output file (was not able to upload the original .PPC3 file but can send via email if necessary).

Thanks and regards,

Craig

hybrid_pwm_pbtl_full.h

Hi Verrill

let me clear some thing for better understanding.

you mean the click sound comes from the power supply, not the connected speaker?

I draw a simple block diagram about your system, am i understanding right?

if you reduce the output power level, does the click sound become smaller or disappear?

if my understanding is not right, can you draw me a simple block of your system.

you can send me the ppc3 file by email. if you cannot solve the problem, i can use your configure with our EVM board to confirm the issue.

thanks.

Jesse

Hi Jesse, 

Your block diagram shows the connections between the input, amplifier and speaker as I have them, but the GPIO1 pin instead goes to the PVDD power supply feedback network. The clicking sound does come from the boost converter that powers PVDD, and it occurs even if no speaker is connected to the system and even if no Bluetooth audio source is connected to the Bluetooth audio sink (input block on the diagram).

Best regards,

Craig 

HI Craig

I am not sure what kind of PVDD power supply device you use.

Is there any instruction of power supply device, does it give any hint about what kind of situation will generate the click? current is too large or the load is too small?

thanks.

Jesse

Hi Jesse,

We are using the LM3478 with 7.2V battery as its input to drive the PVDD power supply. There is a PDF schematic attached to the initial question showing our schematics for the audio and power stages. 

I separated the audio amplifier hybrid PWM signal from the boost feedback and checked the boost and audio stages independently. I saw that the hybrid PWM signal looked as described and the boost converter was generally quiet but occasionally made an audible click sound. Next I looked at the compensation network on the boost stage and saw that it was generally steady and regulated (with hybrid PWM disconnected from FB still)  at 0.828V but would occasionally spike up to 1.4V and that coincided with the timing of the clicks I hear.

Based on that observation, I'm pretty sure the issue is in my boost compensation network on the LM3478. After reconnecting the hybrid PWM signal to the FB network, I looked at the compensation network voltage again and saw that it was all over the place, switching rapidly between around 0.8V and 1.4V.

Is there any special guidance on choosing the compensation components once the Hybrid PWM feature comes into play? Can you double-check the compensation with me and help determine if it should work or if its way off?

Thanks and regards,

Craig

Hi Craig

Can you provide me the circuit schematic by e-mail?

My e-mail is jesse-ji@ti.com.

myside is mainly focus on the amplifier related issue, if the problem is related to how to use LM3478, I am not sure whether need to transfer to other department to support you.

if possible, please let me confirm the circuit schematic including the power supply and audio amplifier part.

By the way, just for confirm, when the click happened, does the audio amplifier work normal or not？

is there any error been triggered?

thanks.

Jesse.