LM3886 Mute

richie00boy · 17th August 2004, 04:32 PM

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.

janneman · 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.

17th August 2004, 04:32 PM	#1
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	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?

17th August 2004, 08:15 PM	#4
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	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. __________________ /Per-Anders (my first name) or P-A as my friends call me

18th August 2004, 11:00 AM	#6
janneman diyAudio Member Join Date: May 2002 Location: Where Germany, The Netherlands and Belgium meet Blog Entries: 6	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 __________________ /Another new issue: Linear Audio Volume 3!

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17th August 2004, 04:37 PM	#2
cm961 diyAudio Member Join Date: Jun 2001 Location: Peterborough, Ontario	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

17th August 2004, 06:05 PM	#3
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	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.

18th August 2004, 09:36 AM	#5
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	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.

18th August 2004, 11:26 AM	#7
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Indeed. I was just on an elimination of parts mission.

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