Hi,
I have created a small test PCB to evaluate the TPA3004D2. My application requires a single (mono) speaker with headphone outputs. I used a slightly modified version of the schematic in figure 36 (page 21) of the TPA3004D2 datasheet. http://www.ti.com/lit/ds/slos407e/slos407e.pdf The main modifications are that I am not using the left channel, so the left channel inputs are AC coupled to ground. The left channel Class D outputs are setup the same as the right channel outputs, execpt instead of driving a speaker, I inserted a dummy load (8 ohm resistor). The left channel VAROUT is terminated with a 10K ohm resistor. The right channel VAROUT output drives both channels of the TPA6110A2 headphone amplifier.
When testing the board with an audio input, the Class D outputs seem to work just fine. However there is no signal coming out of either of the VAROUT outputs. I have tried every possible combination of voltages (within the range of 0-VREF) on VARDIFF, VARMAX, and VOLUME pins, but the VAROUT pins remain constant with only a DC voltage of approximately 2.5V (same voltage as on the V2P5 pin). I used an oscilloscope to probe the VAROUT traces both before and after the DC blocking capacitors. I have also verified that the physical PCB traces were ok and not shorted to ground or any other pin/trace. I thought that maybe the the VAROUT circuit was somehow damaged in the IC, so I replaced the TPA3004D2 with a new chip and the new chip performs in the exact same way.
Do you know of any possible cause for the VAROUT outputs not working?
