lm3886 single sided pcb

[ryan750]

hi guys,

please check my one sided LM3886 pcb layout, thanks



here is the schematic



note: input potentiometer is omitted on the pcb

[AndrewT]

Hi,
you pulled the schematic from the National datasheet.
But, you forgot to read the rest of the datasheet.
As a result you have omitted many components that are recommended by National.
Start again.

[ryan750]

thanks andrew

i've updated the schematics, hope this okay

[MJL21193]

Hi,
You might want to consider splitting the ground into signal ground and common ground. Separate the two with a low value resistor 10R - 22R.
Like this:

[ryan750]

@MJL21193
what would be the benefit of that??

btw: i've made a pcb layout, any comments??

[pacificblue]

Big, unconnected copper areas are an absolute no, no. Either connect them to ground or use that space to make some fixing holes.

Leave some room between the copper and the PCB's border. Remember that a PCB will be produced on a bigger piece of board, which will later be cut to size. Copper right at the cutting edge is likely to be damaged during that process.

Try to keep straight paths at right angles, and make turns at 2x45°. Looks also count. And put yourself into the place of an electron. You are travelling through the copper at nearly the speed of light, and then suddenly there is a 90° turn in front of you. Boy, will you hit your head.

click me

The resistor between signal and power ground can help you with hum issues. You may not need it, but your PCB should be prepared to refit it.

[TheSeekerr]

Just a friendly reminder, and I quote from wikipedia, because my physics textbooks are too far away from my desk:

http://en.wikipedia.org/wiki/Electric_current#The_drift_speed_of_electric_charg es

Electric currents in solids typically flow very slowly. For example, in a copper wire of cross-section 0.5 mm², carrying a current of 5 A, the drift velocity of the electrons is of the order of a millimetre per second

It is only when considering group velocity that electric current moves rapidly (think of toppling dominoes).

For High Frequency work, those layout guidelines matter. For audio, not so much - just look at the sample PCB's in the datasheets for some of the National chipamps. You're quoting from a guide to switchmode power supplies, which are indeed high frequency devices.

All that said, I hate it when components on a PCB don't sit straight, and I'd never make one up from random angles myself, but that's for purely aesthetic reasons. If it looks good, it'll work well, everything else being correct.

[ryan750]

thanks for the reply guys,

here is the updated pcb layout, anything wrong??

[AndrewT]

Pin 7 to power ground. The currents from this pin are not clean.

0u1F decoupling? On the back adjacent to the chips power pins?
Use the space just to the left of pin 2 to insert these small decoupling caps. Tie the junction of these caps to the power ground using a short link.

Zobel from output to power ground?

Remove the trace from power ground to signal ground. Insert a pair of holes for a link/resistor to tie these together.

There are sufficient pins to support this chip to the PCB. Break off the three unused pins and use the space freed up to ease your routing.

Q.)
Where should pin 8 go? Is it clean enough to tie into the signal ground or should it go to the power ground?

[ryan750]

hi,

i this ok??



0.1uf wil be soldered directly to the chip