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Old 17th August 2004, 04:32 PM   #1
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Default 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?
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Old 17th August 2004, 04:37 PM   #2
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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.

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Old 17th August 2004, 06:05 PM   #3
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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.
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Old 17th August 2004, 08:15 PM   #4
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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.
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Old 18th August 2004, 09:36 AM   #5
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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.
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Old 18th August 2004, 11:00 AM   #6
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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.

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Old 18th August 2004, 11:26 AM   #7
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Indeed. I was just on an elimination of parts mission.
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