I am using one of these chips to drive some small speakers in an FM audio receiver.
I notice a burst of oscillation at the zero crossing points when I drive the LM4875 with a sine wave. I can hear the bursts as a roughness in the audio. The real problem comes when the receiver is quietened, carrier up but with no modulation and the zero crossings from noise cause bursts of oscillations with a correspondingly poor SNR. When there is no audio input, I can see a 12 MHz waveform about 200mVpp across the speakers.
I have the vol control at max, 3.6V supply, 68u and 100n decouplers right up on the chip.
If I replace the speakers with an 8Ohm pot, same problem. Change the supply voltage, freq of oscillations change a bit (about 5 MHz).
Speakers are about 35 Ohms each. Happens at all drive levels but sounds worse at low volumes.
Data sheet does not suggest it but should I terminate the speaker output at HFs with a cap and low value resistor in parallel with the LS?
Help appreciated, this product is ramping up for production.