[alsa-devel] USB asynchronous mode feedback format

Julian Scheel julian at jusst.de
Thu Oct 14 22:14:23 CEST 2010

Am Donnerstag, 14. Oktober 2010, 18:11:23 schrieb Daniel Mack:
> On Thu, Oct 14, 2010 at 05:54:35PM +0200, Julian Scheel wrote:
> > Am Donnerstag, 14. Oktober 2010, 17:39:13 schrieb Daniel Mack:
> > > What about the voltage levels? Are they within the specs? I had a quick
> > > look and it seems that Vdd on the codec has to be within 3.0 .. 3.6V,
> > > while the signals you provide rather seem to be in the range of 5V? The
> > > absolute maximum ratings say that Vdd must not be greater than 4.0V.
> > 
> > This might indeed be an issue. The clock signals have about 5V level...
> > The data coming from the uC still has 4.2V
> > This might be too much... Stays the question how to lower the voltage
> > properly there... Any suggestions?
> This get more and more off-topic for the ALSA community, but ...

Indeed sorry for that...
> For the signals, use a voltage shifter, something like the 74LVC2T45.
> For Vdd, if you have to provide that to the board, use a proper
> switching power regulator with low ripple, or an LDO, and care well for
> blocking.

Even found an easier way, at least for the clock signals. As they are 
generated from a 74HCT4060 right now they are 5V. Replacing it with a 74HC4060 
(or 4040) will allow me to reduce Vcc to 3V, so that the output will match.
Thanks anyway...
> Also check whether the voltages you applied all the time could have
> damaged the chip permanently.

Will check it... Have another board in backup for the worst case.

Thanks so far... (c:

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