PAM8403 Schematic Help

[aSpoink]

Im currently designing a PCB that will utilize the PAM8403 for audio. Right now im just worried that my wiring may be incorrect. I would appreciate it if someone could tell me if everything is right and won't blow up when I wire it up.

Thanks!

[iamdarkyoshi]

A good place to start is the application note in the datasheet. I'd assume you've rebuilt that here?

[mariushm]

So you basically copied the schematic from here : https://www.sunrom.com/p/stereo-audio-amplifier-pam8403

 

In your picture, the VDD goes to GND and there's a resistor on it which shouldn't exist, that seems wrong to me. It goes to AVDD which can be the same as PVDD (though often someone uses a LDO to filter the 5v to 4.8v or something like that to reduce/filter noise coming from switching power supplies but this audio amp. chip is not high end in the first place.

 

Also look at the datasheet and the suggestions and notes : https://www.diodes.com/assets/Datasheets/PAM8403.pdf

They use 0.47 uF instead of 220nF on the inputs, which sounds more right to me, and the resistors may need to be slightly higher than 10k on the input channels, maybe 18-22k

 

[aSpoink]

22 hours ago, mariushm said:

So you basically copied the schematic from here : https://www.sunrom.com/p/stereo-audio-amplifier-pam8403

 

In your picture, the VDD goes to GND and there's a resistor on it which shouldn't exist, that seems wrong to me. It goes to AVDD which can be the same as PVDD (though often someone uses a LDO to filter the 5v to 4.8v or something like that to reduce/filter noise coming from switching power supplies but this audio amp. chip is not high end in the first place.

 

Also look at the datasheet and the suggestions and notes : https://www.diodes.com/assets/Datasheets/PAM8403.pdf

They use 0.47 uF instead of 220nF on the inputs, which sounds more right to me, and the resistors may need to be slightly higher than 10k on the input channels, maybe 18-22k

 

How does this look?

I changed the capacitors and resistors on the L and R inputs to what you suggested. I also re-did the VDD and I think its fine now.

[mariushm]

Why is there a capacitor in series on the VDD line ?  A capacitor placed like that blocks DC voltage, so your chip won't receive any voltage on the VDD pin.

 

The datasheet and the other schematic shows the VDD (or better AVDD single it's analogue voltage input) tied to the PVDD (power voltage input), like i said they pretty much only make it available separately in case you have a higher quality voltage (filtered by a linear regulator or something) to feed the internals separately from the big power amplifier part.

In your case, you can power both from same 5v source, so connect AVDD to PVDD and don't worry so much about it.  I don't know what  C35V means, hope you don't give the chip 35v through that pin, you'll blow it up.

 

You could add a 0.1uF ceramic capacitor between PGND and PVDD+AVDD pins, as close as possible to the pins, and very close to that 1uF C11 capacitor... for decoupling purposes, probably won't make any difference but also won't hurt it and such ceramic capacitors are super cheap, pennies.

 

[aSpoink]

18 hours ago, mariushm said:

Why is there a capacitor in series on the VDD line ?  A capacitor placed like that blocks DC voltage, so your chip won't receive any voltage on the VDD pin.

 

The datasheet and the other schematic shows the VDD (or better AVDD single it's analogue voltage input) tied to the PVDD (power voltage input), like i said they pretty much only make it available separately in case you have a higher quality voltage (filtered by a linear regulator or something) to feed the internals separately from the big power amplifier part.

In your case, you can power both from same 5v source, so connect AVDD to PVDD and don't worry so much about it.  I don't know what  C35V means, hope you don't give the chip 35v through that pin, you'll blow it up.

 

You could add a 0.1uF ceramic capacitor between PGND and PVDD+AVDD pins, as close as possible to the pins, and very close to that 1uF C11 capacitor... for decoupling purposes, probably won't make any difference but also won't hurt it and such ceramic capacitors are super cheap, pennies.

 

Hopefully this is correct? Should AVDD be connected to PVDD1 aswell?

[mariushm]

You added a trace that goes from VDD to a side of C11 which goes to ground, so basically you connected VDD to GND, shorting it.  There's no point to that trace

 

You also have the 10uF capacitors with the positive side connected to ground.  The positive goes to input voltage side.

Ideally, these capacitors should be of CERAMIC type (with a voltage rating of 25v or higher) in which case there's no polarity. You can go with electrolytic capacitors (rated for at least 10v or higher) but ceramic capacitors would be better at filtering noise from the power supply

 

I've corrected the schematic in paint :

 

 

 

much later edit : tiny mistake in the picture,  i flipped the text labels for ROUT- and ROUT+ in the picture by accident, rout- is the wire on the left and rout+ is the one on the right, it basically mirrors the left side of the chip.

 

Some further thoughts.

 

The circuit in the schematic and the one from the link above assume you're going to power the amplifier from batteries which are less noisy. If you're gonna power it from a USB charger or some 5v switching power supply) it would help to add an electrolytic capacitor between 5v and ground near the power connector, with the positive side at the 5v pin. Anything between let's say 100uF and 1000uF (and rated for 10v or higher) would be OK, but above around 470uF you won't get any noticeable improvements. Personally I would use 220uF or 470uF 25v rated since they should be very common and cheap, but you could take out a 1000uF 10v / 16v capacitor from some old or broken  computer power supply and it would still be OK to use

 

If you plan to power this with batteries, you would still get slightly longer battery life by adding a capacitor at the input but it should be smaller, maybe up to 100-220uF - the capacitor acts as a small buffer of energy and helps even out the amount of energy pulled from batteries, batteries can provide energy for longer time if the draw is more steady instead of lots of sudden bursts of power draw  (when you have some beats of drums on the sound for example)

 

The ground at the capacitor in series with the VREF pin should be connected with ground from pin 11 and the NC pin (9) to the audio ground (the ground of the line in cable) and then to the power ground (the ground of battery or power supply)

 

 

[Unimportant]

@aSpoink

Board layout is also important in this case. The bypass capacitors should be as close as possible to the actual pins they're connected to, using wide traces to lower parasitic inductance and resistance. The power grounds and supply (PVDD/PVDD1, PGND/PGND1) should be connected either in a star formation (single sided PCB) or large power planes (double layer/multilayer) with multiple via's in parallel where via's are required. Never connect such power pins with a single trace going from one pin to the next, as any voltage drops caused by parasitic inductance/resistance in the trace by whatever is on the end of the trace will affect all other devices along the trace.

 

You're also dealing with 2 key frequency ranges. The (low) audio frequencies and the (high) switching/carrier frequency. Different kinds of bypass capacitors should be used on the power pins in parallel. Electrolytic bulk capacitors for the low audio frequencies and ceramic caps to handle the high switching noise.

[mariushm]

@Unimportant it's a very good advice, but not so important in this particular case, as we're dealing with a simple 5v 2x 2-3w audio amplifier. It's not high end enough for the suggestions you make to really make any difference.

He can make it single layer or double layer, you can see it obviously works reasonably well with just ceramic capacitors as the model i linked to in my first post on sunrom.com shows.  For start, just keep it simple and make it, then you can improve on your design if you really think it's worth it.

 

My 2 cents... just go for a higher end audio amplifier chip if you want higher quality.

[Unimportant]

20 minutes ago, mariushm said:

@Unimportant it's a very good advice, but not so important in this particular case, as we're dealing with a simple 5v 2x 2-3w audio amplifier. It's not high end enough for the suggestions you make to really make any difference.

He can make it single layer or double layer, you can see it obviously works reasonably well with just ceramic capacitors as the model i linked to in my first post on sunrom.com shows.  For start, just keep it simple and make it, then you can improve on your design if you really think it's worth it.

 

My 2 cents... just go for a higher end audio amplifier chip if you want higher quality.

Indeed, it'll probably be OK, but it's still switching about 1A (both channels combined) at high frequency when running at full power. That's enough to cause SCR latchup if you manage to make a really bad PCB design. Why not learn that these things matter from the start ?