TPA3118D2: Why the output power is so high?

Went Cao

Part Number: TPA3118D2

Dear All

My speaker spec is 8Ω, but when the video input is high frequence, like 14KHz,the speaker load will change to 2Ω, the voltage of OUTNR with OUTNL will change to 100V, Why ? The normal voltage is 40V in 8Ω.

I had set the GAIN/SLV pin to 20W, the maximum output power is 20W,right?

over 7 years ago

0 Shawn Zheng over 7 years ago

TI__Mastermind 24835 points

Hi Went,
I think it could be caused by the resonance of the LC filter. You could adjust the Q value of LC filter to achieve a flat frequency response across audio band. We have a document and tool for the LC filter design. Please be noted that the speaker is considered as a pure ressistor in it and the real speaker could make a little difference. www.ti.com/.../slaa701a.pdf www.ti.com/.../slac729
GAIN/SLV pin is used to select the gain setting and slave/master mode, but not the output power. Please refer to the section 7.3.1 in the datasheet.
Best regards,
Shawn Zheng

0 Went Cao over 7 years ago in reply to Shawn Zheng

Genius 5550 points

Dear Shawn

The output power is U*U/R, right? So the output is up to 100V*100V/2Ω,right ?

Sorry, I set the PLIMT pin to limit output to 20W.

0 Shawn Zheng over 7 years ago in reply to Went Cao

TI__Mastermind 24835 points

Hi Vent,
Are you using a transformer？ How much is the PVCC voltage in this application? Please show your SCH if possible.
Best regards,
Shawn Zheng

0 Went Cao over 7 years ago in reply to Shawn Zheng

Genius 5550 points

Dear Shawn

Sorry for late.

What is the transformer? Below is my SCH,please check it. and the PVCC voltage is 24VDC.

0 Shawn Zheng over 7 years ago in reply to Went Cao

TI__Mastermind 24835 points

Hi Went,
I see that 1nF caps are used in the output filter, may I know inductors or ferrite beads are used on the output? If inductors are used, please use 10uH+0.69uF configuration or ferrite_bead + 1nF for the output filter.
Best regards,
Shawn Zheng

0 Went Cao over 7 years ago in reply to Shawn Zheng

Genius 5550 points

Dear Shawn

Thank you very much. I will try it.

And,could you answer to me the below question? Thanks.

0 Shawn Zheng over 7 years ago in reply to Went Cao

TI__Mastermind 24835 points

Hi Went,
The output power Po = Urms*Urms/R.
Best regards,
Shawn Zheng

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TPA3118D2: Why the output power is so high?