LM3886 GND pin

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From the datasheet and internal schematic of the LM3886 it can be seen that the GND pin has several functions.

1 - its voltage vs. the V- pin is monitored, keeping the chip in mute mode when it is less than 9V.

2 - it defines the output potential in mute/startup mode. Note the 10k on the left side of the inner diff amplifier. This diff provides a closed feedback loop in mute mode with the right hand 10k and the clamping diodes. These diodes go to ground, thus in normal operation there is a current path from the output to GND, via the 10k, about 0.1mA per Volt of output voltage.

3 - it's the reference potential for the mute logic. When current is drawn from the mute pin (towards V-) in the ON mode, the startup diff's current source gets turned off by the grounded base transistor on the left. The GND pin provides the base current for it.

4 - there must be something missing here, because from the single-supply schematic I realize that the GND pin shall only sink current in normal operation. OTOH, that schem might be wrong/flawed.


Especially point #2 indicates that the current into/out of the GND pin should not be routed to signal GND, in theory, as this nonlinear current might contaminate the signal GND. In fact it's so small (well below 10mA) that this is not a problem in a proper design/layout. Likewise, if this GND pin carries some noise, it won't affect operation -- but avoid excessive HF noise, of course.

So, my 2 cts:
If you have the option, don't bond it to signal GND. But don't sacrfice a good layout just for that tidbit.

Regards, Klaus
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Non so a quale datasheet faccia riferimento, ma facciamo a fidarsi.