TAS2505: Adverse effects of output pin Overshoot

Ryotaro Fukui

Part Number: TAS2505

Hello team,

I would like to ask some questions about the overshoot in the output pin of TAS2505.

1. What are the absolute maximum rating of outputs SPK-P / M pins?

My customers are worried that the overshoot and undershoot may be too big to break the device. At present, a voltage of about 7.4V is generated at the peak. Please refer to the attached file for the waveform.

2. I also found a statement in the E2E forum that device will not break at this level of overshoots, but is that true on this case too?

https://e2e.ti.com/support/audio/f/6/t/915514

3. Does the slow rise caused by the capacitor have an adverse effect on operation?

They are also planning to add a capacitor to suppress overshoot, and it seems that they confirmed the improvement of the waveform by attaching 22000pF to GND.
However, since the rise is slow (about 40nS), they are worried that this may have an adverse effect. Looking at the EVM, the SPK-P and SPK-M signal lines have a 4KΩ + 0.022uF filter, but if there is a recommended external circuit, please let me know.

I am looking forward to hearing from you.

Best Regards,

Ryotaro Fukui

TAS2505WaveformDistortion.xlsx

over 4 years ago

0 Luis Fernando Rodriguez S. over 4 years ago

TI__Guru* 84915 points

Hi, Fukui-san,

Thank you for contacting us.

I will take a look at this and will provide a response as soon as possible.

Best regards,
Luis Fernando Rodríguez S.

0 Ryotaro Fukui over 4 years ago in reply to Luis Fernando Rodriguez S.

TI__Intellectual 2345 points

Hi, Luis-san,

Thank you very much. I am very grateful for your prompt reply.

Actually, the customer wants a early feedback, and we would appreciate it if you could give us any kind of brief feedback soon.

I am looking forward to hearing from you.

Best Regards,
Ryotaro Fukui

0 Luis Fernando Rodriguez S. over 4 years ago in reply to Ryotaro Fukui

TI__Guru* 84915 points

Hi, Fukui-san,

The maximum output level that the speaker driver outputs can reach is SPKVDD. As stated in the datasheet, the absolute maximum rating for SPKVDD is -0.3V and +6V. While the SPKVDD doesn't reach these levels, there won't be risk of damage due to an overshoot.

Regarding the question regarding the capacitor, we usually don't recommend to connect it directly at the speaker driver since it may result in an overcurrent event. If necessary, an LC filter can be used to mitigate overshoots and EMI issues. For more details, please take a look at the document and tool below:

https://www.ti.com/lit/an/slaa701a/slaa701a.pdf

https://www.ti.com/tool/LCFILTER-CALC-TOOL

Best regards,
Luis Fernando Rodríguez S.

0 Ryotaro Fukui over 4 years ago in reply to Luis Fernando Rodriguez S.

TI__Intellectual 2345 points

Hi, Luis-san,

Thank you for the advice. Let me confirm if my understandings are correct.

So, whether or not a device breaks depends only on the voltage of SPK VDD, and the output SPK-M / P has no effect no matter how much it overshoots, right?
However, overshoots cause overcurrent, so they should use an LC filter if possible.
Also in the schematic of TAS2505EVM (https://www.tij.co.jp/jp/lit/ug/slau498a/slau498a.pdf#page=7), at bottom left of the graph(near J6, J7), there are RC next to SPK-M/P. How should they handle this? Should they remove the RC and install the LC instead?

It may be a rudimentary question, but it would be helpful if you could confirm it.

Best Regards,
Ryotaro Fukui

0 Luis Fernando Rodriguez S. over 4 years ago in reply to Ryotaro Fukui

TI__Guru* 84915 points

Hi, Fukui-san,

Your understanding is all correct.

Regarding your question about the RC filter, this filter is actually used for measurement purposes. The RC filter removes the Class-D activity switching frequency so the output can be measured by the oscilloscope.

If the customer won't perform audio measurements, he can remove this RC filter. The LC filter will be used to mitigate EMI issues.

Best regards,
Luis Fernando Rodríguez S.

0 Ryotaro Fukui over 4 years ago in reply to Luis Fernando Rodriguez S.

TI__Intellectual 2345 points

Hi, Luis-san,

I'm glad to hear that.

They were trying to deal with the overshoot to avoid device failure, but since there is no risk about it, I think the customer's concern will be resolved.

I also understand they wouldn't need a RC filter too. I would just recommend the LC filter instead.

Thank you for all your advice.

Best Regards,
Ryotaro Fukui

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TAS2505: Adverse effects of output pin Overshoot