I have made a PCB with the sample circuit in the data sheet. I am using 9, 10, 11 or 12V for the power supply voltage. I am using 1uF film caps t block DC at the inputs. I am using 20dB gain so it has about a 60K input impedance. This makes an input filter that is a little higher than 1Hz but no so much that a 1 Hz signal would disappear. I am using either 10uH or 33uH inductors with caps as output filters. I have designed and built 2 different PCB's with the same amplifier circuit and the amp works as expected almost. Frequencies above say 10Hz get amplified and the chip delivers the appropriate PWM output. The DC offset on the input pins is close enough to 3V that I think it is fine with respect to the data sheet. When I lower the input frequency to 1 Hz without changing the amplitude of the input or the circuitry of the amp the input stage seems to die. I say die because the DC offset at the input pins goes to about 0 V. This is a permanent thing. Moving the frequency back up to 10Hz or above does not result in the DC at the inputs going back to normal and the output is no longer there. Has anyone seen this kind of behavior. This happened on the 2 different PCB's and 3 parts as I relaced 1 after it went bad.
Mark Allie
