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Disclaimer: I know you aren't supposed to ask about specific IC's as it is not helpful to the community in general, but I am at my wit's end here so I will try to make this as relevant as possible.

I would like to add audio to a good ol' Raspberry Pi Zero. Specifically I would like to take the audio generated by the PWM pins (GPIO 18 and 19) and feed them into a small 8 ohm speaker and a headphone jack. To do this with the raspberry pi an amplifier would need to be used. I would like to use one amplifier for both outputs so I can control the volume of both outputs with one potentiometer on the input to the amplifier.

I found one family of amplifiers that I thought could do the trick, namely the Diodes Inc. PAM8009. The PAM8019 would also work, but it has the same issues. The problem is that I don't know what to do for the Undervoltage Protection (UVP) pin. There is a small circuit connected to the pin with three resistors and it gives a couple of equations for desired UVP voltage and hysteresis. The problem is that I don't know enough about audio AMPs to know what my desired UVP voltage and hysteresis should be, much less the values of the three resistors. Sadly, Diodes does not provide an evaluation board for this chip and my attempts to contact them have gone unanswered for weeks. They have no public forums to seek help from other people. I really have no idea what their values should be and I don't want to apply a "try random values and see what happens" approach if it can be avoided.

If you know of another amplifier that can do the trick that does not use I2C control for amp volume (because I don't want to have to right a driver for that and the I2C buses already have a few devices on them) then please let me know. Otherwise any help with the PAM8009 would be greatly appreciated.

Again I know this may be against the posting rules, but this is the last place I can turn to for help. If you know somewhere better to ask then let me know.

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  • \$\begingroup\$ In the UVP pin description, it says 'floating or pull high to disable the protection'. Is that all you need? \$\endgroup\$ – Neil_UK Nov 18 '16 at 8:03
  • \$\begingroup\$ spec says pull UVP high to disable \$\endgroup\$ – Sunnyskyguy EE75 Nov 18 '16 at 8:09
  • \$\begingroup\$ That's true, but since it protects from the popping that occurs when you plug in headphones I would prefer to have it. \$\endgroup\$ – Nate Nov 18 '16 at 9:09
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The Undervoltage Protection (UVP) function is intended to avoid noises on the speakers during the power-up and power-down phases. If you provide a low voltage on the UVP pin, the amplifier will be muted, and noises will be avoided.

If these noises are not an issue for you, you simply can ignore this function, and disable it leaving the pin open, or connecting it to a logic high level.

If instead you have to avoid the noises, that can rise for instance from uncontrolled voltages on the PWM pins during power up, you must find a way to provide a control voltage on the UVP pin; the simple circuit with resistors and capacitor illustrated on the datasheet can do the job. You can start with 100k for R3 and 10k for R1 and R2, and then adjust the values experimentally.

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  • \$\begingroup\$ Call me stupid but I want to confirm, does this mean I need a regulated voltage < VCC for the UVP pin (1.2V is recommended I think)? If so then what is a rough estimate for "good" hysteresis? I have a vague understanding of hysteresis but don't really know what a good value for it is. \$\endgroup\$ – Nate Nov 18 '16 at 9:12
  • \$\begingroup\$ Hysteresis gives you the possibility to have different values of voltage to switch on and off. It is obtained via a small current (6 uA) on the series resistor R3. If your problem is simply to avoid pop noises, you can simply ignore this details. \$\endgroup\$ – CasaMich Nov 18 '16 at 9:24

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