Can anyone help me with this: plss?
I took a look at LM3886 datasheet, and try to calculate the value of it’s Mute Resistor (Rm) but I am not sure if I done it right, so if it is ok with you, can you post here an example of calculation of the Mute Resistor of LM3886? Suppose you will use +28, 0,-28 volts power supply, because it is said in the datasheet that Rm is chosen with the reference with the negative supply voltage.
And say that I don’t want to use the mute function, so I have to connect the mute resistor directly to negative supply voltage? Or I don’t have to use a mute resistor and I will just connect Pin 8 directly to negative supply voltage? Tnx in advance!
I took a look at LM3886 datasheet, and try to calculate the value of it’s Mute Resistor (Rm) but I am not sure if I done it right, so if it is ok with you, can you post here an example of calculation of the Mute Resistor of LM3886? Suppose you will use +28, 0,-28 volts power supply, because it is said in the datasheet that Rm is chosen with the reference with the negative supply voltage.
And say that I don’t want to use the mute function, so I have to connect the mute resistor directly to negative supply voltage? Or I don’t have to use a mute resistor and I will just connect Pin 8 directly to negative supply voltage? Tnx in advance!
Can anyone help me with this: plss?
I took a look at LM3886 datasheet, and try to calculate the value of it’s Mute Resistor (Rm) but I am not sure if I done it right, so if it is ok with you, can you post here an example of calculation of the Mute Resistor of LM3886? Suppose you will use +28, 0,-28 volts power supply, because it is said in the datasheet that Rm is chosen with the reference with the negative supply voltage.
And say that I don’t want to use the mute function, so I have to connect the mute resistor directly to negative supply voltage? Or I don’t have to use a mute resistor and I will just connect Pin 8 directly to negative supply voltage? Tnx in advance!
I took a look at LM3886 datasheet, and try to calculate the value of it’s Mute Resistor (Rm) but I am not sure if I done it right, so if it is ok with you, can you post here an example of calculation of the Mute Resistor of LM3886? Suppose you will use +28, 0,-28 volts power supply, because it is said in the datasheet that Rm is chosen with the reference with the negative supply voltage.
And say that I don’t want to use the mute function, so I have to connect the mute resistor directly to negative supply voltage? Or I don’t have to use a mute resistor and I will just connect Pin 8 directly to negative supply voltage? Tnx in advance!
Data sheet says:
Mute resistance set up to allow 0.5 mA to be drawn from pin 8 to turn the muting function off.
If you take some margin and design for 1mA, with -28V, 28k from pin 8 to -28 should do it. So would a standard R of 33k.
Jan
Mute resistance set up to allow 0.5 mA to be drawn from pin 8 to turn the muting function off.
If you take some margin and design for 1mA, with -28V, 28k from pin 8 to -28 should do it. So would a standard R of 33k.
Jan
Setting the mute current value affects the way the 3886 switches off as well as the way it switches on.
Setting mute current high, holds the amplifier in the operating state when the supply rails have fallen low during the OFF period. The capacitor in the mute circuit extends this "on" period.
Aim to exceed the 0.2mA by a significant margin.
2x, or 3x, might be good enough to ensure the mute is fully unmuted, even when supply rails sag during high volume reproduction.
Setting to 5x, i.e. 1mA means that the 0.2mA mute current will still be flowing when the supply rails have fallen to 20% of their nominal value. This will usually result in the -9Vdc trigger for amplifier switch off occurring first. Is this a quiet shut down mode? Will the amplifier still be stable when the supply rails are at 50% of nominal, or at 30% of nominal. Will the treble speaker be affected by a short period of whistling during shut donw?
Setting mute current high, holds the amplifier in the operating state when the supply rails have fallen low during the OFF period. The capacitor in the mute circuit extends this "on" period.
Aim to exceed the 0.2mA by a significant margin.
2x, or 3x, might be good enough to ensure the mute is fully unmuted, even when supply rails sag during high volume reproduction.
Setting to 5x, i.e. 1mA means that the 0.2mA mute current will still be flowing when the supply rails have fallen to 20% of their nominal value. This will usually result in the -9Vdc trigger for amplifier switch off occurring first. Is this a quiet shut down mode? Will the amplifier still be stable when the supply rails are at 50% of nominal, or at 30% of nominal. Will the treble speaker be affected by a short period of whistling during shut donw?
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Now, to answer your question...
The specs in the data sheet are measured with Imute = 500 uA, where Imute is the current from the MUTE pin to V-. I recommend designing for Imute = 500 uA at about 2/3 the nominal supply voltage. I use 2/3 because it gives 1/3 of the nominal supply voltage to account for droop, ripple, low mains supply, etc.
I describe how the mute circuit works on my Taming the LM3886, Grounding Page. There's a 3 V drop across the internal circuitry in the LM3886. Hence, the mute resistor can be calculated as:
Rmute = ((2/3)*VCC - 3)/Imute
For a +/-28 V supply and Imute = 500 uA, the math is:
Rmute = ((2/3)*28 - 3)/0.0005 = 31333 ohm
I'd use 30 kohm (5 % standard value) or 27 kohm (10 % standard value).
The second part of your question: Yes. You have to use a mute resistor. Otherwise, you'll very likely blow the internal mute circuitry as a rather large current will be drawn through the mute pin and associated internal devices.
Tom
The specs in the data sheet are measured with Imute = 500 uA, where Imute is the current from the MUTE pin to V-. I recommend designing for Imute = 500 uA at about 2/3 the nominal supply voltage. I use 2/3 because it gives 1/3 of the nominal supply voltage to account for droop, ripple, low mains supply, etc.
I describe how the mute circuit works on my Taming the LM3886, Grounding Page. There's a 3 V drop across the internal circuitry in the LM3886. Hence, the mute resistor can be calculated as:
Rmute = ((2/3)*VCC - 3)/Imute
For a +/-28 V supply and Imute = 500 uA, the math is:
Rmute = ((2/3)*28 - 3)/0.0005 = 31333 ohm
I'd use 30 kohm (5 % standard value) or 27 kohm (10 % standard value).
The second part of your question: Yes. You have to use a mute resistor. Otherwise, you'll very likely blow the internal mute circuitry as a rather large current will be drawn through the mute pin and associated internal devices.
Tom
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