I'm building a 6 channel circuit with the PAM8403 (Filterless 3W Class-D Stereo audio amplifier) and was wondering if I could make things more compact by using less components. Is it possible to combine some capacitors between the amplifiers? Which ones and how would the values change? My power supply is 5V 500mA lithium battery and I'm using a combination of 3x PAM8403. Below is my schematic:
I would not share the capacitors that are in the signal path (connected to IN1, IN2) as combining them means that the inputs of the amplifiers are not AC coupled anymore so a DC offset from one amplifier can influence another amplifier.
I would also not share the capacitor on the VREF pin. Note that you have used 1 uF on VREF while in the datasheet 0.1 uF is used.
You could share some of the supply decoupling capacitors between 5 V and ground. I would give each amplifier chip it's "own" 2x 1 uF capacitor at the PVDD and PVDD1 pins. These 1 uF caps need to be close to the PVVD and PVVD1 pins of the IC so that current loops are small, this reduces EMI emissions. Also the ground connection needs to be as short as possible. The best solution is to use a ground plane.
The other capacitors of 10 uF and 1000 uF can be shared I think. The datasheet lists that you need 470 uF per amplifier IC, you could do that but you probably can get away with using one 1000uF or two 470 uF shared between all three amplifier ICs.
Do note that class D amplifiers like this one can be critical (sensitive) to the PCB layout due to the switching at the output. If possible look at some layout examples of similar chips (unfortunately the PAM8403's datasheet does not show an example layout) to see how it is done. When the layout is wrong you risk all kinds of nasty behavior like oscillations and noise.