I'm using the TPA6021A4 in an audio application. I'm feeding this from a I2S DAC chip. I've tried both CS4334 and MAX5555 with the same results. I seem to be getting clipping I'm using a sine wave to test the circuit. My TPA6021A4 is connected per Figure 19 in the datasheet, p. 11. The connection between it and the DAC is shown in the attached schematic.jpg. I've also attached two scope traces. Both have the yellow trace as the DAC output after the RC filter before the 0.47uF cap. The green trace is the output of the amplifier. "sine-gnd-bypass.jpg" occurs when "Lin -" is hooked per the TPA datasheet, bypassed to gnd with 0.47uF. "sine-floating.jpg" occurs when I unhook the Lin - capacitor and let the line float. The clipping disappears but full volume isn't achieved. If I reduce the volume enough the clipping goes away, but then the output is not very loud at all. Any recommendations to get this amp working without the clipping?
What is your supply voltage and gain setting? I assume you have configured the Amplifier in BTL mode? What speaker impedance are you using? I can't see the scaling on your scope capture very well, but it seems to be 2V/div?
Audio applications Engineer
Dallas, TX - USA
Thanks for the reply. My supply voltage is 5v. I am using BTL mode. Everything is just like it shows in the example schematic. I'm using 4ohm speakers. The scaling is 2V/div. The input signal is ~3.2Vpp and the output being clipped is ~5Vpp. I'm using maximium gain, eg. 5v on volume pin. I can reduce the clipping by lowering the volume pin voltage or by adding some resistors to lower voltage of the input signal. The problem is that then the resulting volume I end up with is way to quiet. Initially I've used this chip with another DAC (differential) and was able to get much more volume.
I suspect my problem has something to do with using a single ended DAC with a differential amplifier. I'm following the interface shown in the datasheet but it dosn't work correctly.
Yes, since you are applying a single-ended signal you will only get half of the output swing. Ideally you would want to lower the gain and apply the input signal differentially, or the amp will clip since you are driving only half of it. You can try lowering your speaker impedance but THD may be compromised.
Further to what Alfredo said... It looks like you are getting rail to rail swing on the output. I think the only way you're going to get more power is to use a higher voltage amplifier. I think if you look at the output differentially (ch1-ch2) and do the math, you'll see you're getting the rated output power, aren't you?
I don't know the exact signal swing (you can calc it based on the plots in the d/s for 4-ohm load), but I'd guess driving 4 ohms you ought to be able to get 4Vpp on each output, which, measured differentially, will result in 8Vpp in BTL mode. By my calculations, this will give you about 2W of output power.
Audio Applications Engineering Manager
Dallas, TX USA
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