Wolfson WM8741 Mono ???

[davecandialex]

I have a question about using this dac in MONO mode. The chip has separate resistor divider mid supply references for left and right channel. A total of six pins used. For mono would it be correct to tie the left and right sets together?

While I am at it, does anybody cut the ground plane for analog and digital now? I don't see that done on their eval board.

[SoNic_real_one]

No, you don't "tie" them toghether! I don't see (in the pdf) any divider for the reference, just capacitors.
For the output you need to do the filter shown on page 62 of that pdf and, at the end of the "unballanced" left and right channels, add one more OpAmp to convert from the differential mono (presnt on the L and R unballanced) to unballanced mono - see the mono mode control register at page 48.

Why would you cut the ground planes? They are tied toghether inside the chip anyway!
Just separate the power supplies positive rails (or at least use an inductance between them, if power for digital comes from the analog side).

[davecandialex]

Originally Posted by SoNic_real_one

No, you don't "tie" them toghether! I don't see (in the pdf) any divider for the reference, just capacitors.
For the output you need to do the filter shown on page 62 of that pdf and, at the end of the "unballanced" left and right channels, add one more OpAmp to convert from the differential mono (presnt on the L and R unballanced) to unballanced mono - see the mono mode control register at page 48.

Why would you cut the ground planes? They are tied toghether inside the chip anyway!
Just separate the power supplies positive rails (or at least use an inductance between them, if power for digital comes from the analog side).

The resistors I refer to are shown in the block diagram, seems like two dividers are used for isolation which would not be needed for mono.


As a guy who design analog/mixed signal chips for a living I would agree that every node and component on a chip are connected at some level. The figure on pg 62 does suggest tying the analog and digital grounds together. Thanks for pointing that out. My last DAC was a PCM1704. It was common back then to split the ground planes and tie at single point.