We have 0.5 Vrms full scale output voltage from headphone amplifier specified for 16 ohm load. Output resistance of the headphone amplifier is 0.3 ohms. We are trying to feed this output to TPA3110D2 for 15W + 15W output into 4 ohms speakers with supply voltage between 12-14V.
What should be the gain setting for TPA3110D2, if we give the above 0.5rms full scale output from the hp amp to the input of TPA3110D2 with 12-14V supply voltage? Output required is 15W into 4 ohms. Appreciate if the calculation is explained. The test data in the datasheet is mainly given for 8 ohms load and not for 4 ohms load.
Is there any benefit if we use a line driver or op-amp and scale up the 0.5Vrms to standard line level 1V or 2V rms?
I think this app note will answer your questions.
Audio Applications Engineering Manager
Dallas, TX USA
Thanks for the app note. It was really helpful. I got the following for my application based on this app note and TPA3110D2 datasheet.
Output Power = 15W
Load Impedance = 4 Ohms
Based on the above VoRMS = 7.75V which is 22vP-P.
Since my supply voltage is 12V, do we need to bring the VoP-P below the supply voltage? If yes, the maximum VoRMS I can have is 4V which is approx 12V P-P. Calculating with VoRMS of 4V and 4 ohms load the max power output is only 4W. Am I missing something?
I think you missed a factor of 2 for BTL operation.
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