Forums - The question on audio block of PM8916

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The question on audio block of PM8916
mavillosangrae
Join Date: 9 Oct 17
Posts: 1
Posted: Mon, 2017-10-09 23:59

 

Hello, my name is Sang-Rae Lee.

My company name is WIZARDLAB in Korea and our company plans to deliver smartwatch for kids to LGU+(service provider) in Korea.

Manufacturer is BORQS in China and our product is including PM8916 of Qualcomm.

So our audio interfaces such as MIC and Speaker are connected to the audio block of PM8916.

Please, refer to below, for more detail informations, problems and questions.

 

   1) Product information related to AUDIO

       (1) Speaker Amplifier : Internal class D audio amplifier in PM8916

       (2) Power Supply for Audio Block in PM8916 : Battery(3.4V ~ 4.2V)

       (3) Speaker Rated Power : 700mW(0.7W)

       (4) The resistance of speaker is 8 ohm. 

   2) Current Problem

       (1) Because battery voltage level is varied from 4.2V to 3.4V, so the output power of amplifier is varied from 956mW to XXX mW(no information at 3.4V) according to datasheet.(3.6V/690mW, 3.8V/720mW, 4.2V/956mW)

       (2) The rated power of our speaker is 700mW.

       (3) So, there is problem related to mismatch between our speaker rated power and the ourput power of audio amplifier.

   3) Question

       (1) We think that the maximum voltage level to satisfy the rated power of our speaker is about 3.6V.

       (2) But as you know, if battery voltage level is more than 3.6V then our speakr may be damaged because the output power of amplifier is more high than speaker rated power.

       (3) We have tried to review datasheet of Qualcomm to discover good methods but we failed to discover due to poor information.

       (4) At current situation, are there any methods which is H/W approach or S/W control approach to solve this problem?

     

Thank you.

 

Best Regards.

Sang Rae Lee.

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jbhanu Moderator
Join Date: 6 Feb 17
Posts: 76
Posted: Wed, 2018-01-03 00:37

Hi Sang Rae Lee, 

This is the limitation of PM8916 audio PA as it’s powered by battery.

 

One possible solution for you is to add external 3.6V DCDC(instead of VPH_PWR) to as power for the VDD_EAR_SPKR.

So that there is fixed 3.6V for PA.

 

On the other side, have you  tried to limit the SPKR_DRV output power/gain so that the output power will not be higher than 700mw from software?

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c_mmudup
Join Date: 1 Jul 15
Posts: 1
Posted: Mon, 2018-01-08 22:59

Dear Sang-Rae Lee,

If PM8916 audio codec BOOST is not used in your HW design then speaker output power will vary according to the battery level.

To avoid this issue your Hardware must have support for codec BOOST in your design.

Thanks & Regards,

Mahender Reddy M

 

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