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-   -   LM3886 Mute (http://www.diyaudio.com/forums/chip-amps/39575-lm3886-mute.html)

richie00boy 17th August 2004 04:32 PM

LM3886 Mute
 
I have been searching the forum on this subject and I have not found the answer. Why can I not just tie the mute pin directly to the -ve rail? If you just need to pass a minimum of 0.5mA why bother with the resistor?

cm961 17th August 2004 04:37 PM

If the pin isn't current limited it could draw a lot of current from -ve and blow up the chip would be my guess. Or it could unevenly load the power supply so that your + and - voltages weren't the same.

Pete

richie00boy 17th August 2004 06:05 PM

Yes. I should have woken up when I looked at the equivalent circuit on the datasheet. With a direct connection there will only be an internal 1k resistor limiting the current, probably resulting in a hot chip if not failure.

peranders 17th August 2004 08:15 PM

As I always nag about: Read the datasheet even though if you don't understand most of it. National's datasheets happen to be very good and this particular issue is clearly written about.

Notice also how this resistor have influence of the gain.

richie00boy 18th August 2004 09:36 AM

I too believe in reading the datasheets :)

The influence of the resistor on the gain was what prompted me to ask the question as I realised that to ensure no attenuation, enough current must flow out the pin. I saw the best way to achieve the absolute least possible attenuation was to just omit the resistor and tie directly to -ve.

jan.didden 18th August 2004 11:00 AM

There is also a graph in the DS for att versus mute current. It is clear that for currents higher than the indicated one, there is no furter change in gain.

jan Didden

richie00boy 18th August 2004 11:26 AM

Indeed. I was just on an elimination of parts mission.


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