Hi team,
My customer is using TPA3111D1 for their 10W output speaker.
They are also looking at controlling the output power at different level with the same input signal and speaker impedance
In one of the application, they want to limit the max output power to 2.5W. They already set the gain at the lowest gain of 20dB. With the same level of input signal, the output power will be around 9W. They are studying on what will be best way to limit the input signal so that could reduce the output power to 2.5W. PLimit is not an option as they will to maintain the THD, as well as no clipping.
They are looking at adding the resistive divider to divide the input signal to ~1/4 to get the 2.5W output, and to ~1/2 to get 5W output. The resistor value is in the range of 10K for R90/91 and 2.7K/9.1K for R at 2.5W/5W output.
what will be the impact on THD and SNR?
Or it will be better to place the resistor divider after the blocking cap, C32?
Or will it be better to add a series resistor after C32 to change the input impedance of the audio amp (at 20dB gain setting, the input resistance is 60K, and with 600K feedback resistor)? is there a max series resistor we can add? In section 7.3.1 in datasheet, it mentioned "at lower gain settings, the input impedance could increase as high as 72K". is this refer to internal impedance, or the external series resistor that I can add?
I'm thinking if we add a 120K series resistor, it could reduce the gain down to 5dB so it will limit the output power to around 2.5W.
