I have designed my own board with the same schematic and layout as the EVM, but as a stereo pair with one chip being master and one being slave.
I tried bringing up my prototype board without any speaker connected, and the snubber resistors smoked and burned up (20 ohms, 1/4 watt, 1206).
I imagine this is because the output filter needs the speaker, but in this case the speaker was not connected.
How do I prevent this from happening when there is no speaker connected? Increase the value of the snubber resistor?
I could try to prove the same thing happens with an unloaded EVM, but I don't want to destroy my reference unit!
I investigated more and found my snubber caps were 100nF instead of 1nF.
I installed C = 1nF and R = 68R, and all is good.
What are good values for C and R at 40W and no speaker load connected?
The snubber values we use in our designs are R = 3.3 Ohm with 5% tolerance, and C = 0.01 uF rated for 100 V, X7R. We've used these values for both 30 W per channel and 50 W per channel designs. We haven't had any issues with these values while having no load. You can give them a try and report back your results here.
Home Audio Applications
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