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Chip Amps Amplifiers based on integrated circuits

Yet another LM3886 Layout. Single-supply
Yet another LM3886 Layout. Single-supply
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Old 7th April 2019, 10:05 AM   #1
kipphebel3 is offline kipphebel3  Aland Islands
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Default Yet another LM3886 Layout. Single-supply

They will sit underneath a small side speaker with a Visaton B80 element. Powered by a small 36V SMPS. This is what I tried to do with this layout.

Using the LM3886 ground pin as a star ground for input, Ri, Ci, Rsn, Csn.

Using SMD components alowing me to put Rf1, Rf2 etc very close to the LM3886 pins.

Cs is a 220u low ESR with a 0.1u MLCC very close to the pins.

C and Ci are polyester caps.

The output cap will be mounted parallell to the board, not standing up to fit the case.

Comments? I can upload the KiCAD files in case anyone is interested.

Edit: The MMBT3904 had the wrong footprint. Will correct
Attached Files
File Type: pdf LM3886-F_SilkS.pdf (22.0 KB, 118 views)
File Type: pdf LM3886-B_Cu.pdf (18.1 KB, 74 views)
File Type: pdf LM3886-F_Cu.pdf (23.7 KB, 58 views)
File Type: pdf LM3886.pdf (23.7 KB, 155 views)

Last edited by kipphebel3; 7th April 2019 at 12:31 PM.
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Old 8th April 2019, 03:49 AM   #2
Tibouchina is offline Tibouchina  Australia
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Originally Posted by kipphebel3 View Post
Comments? I can upload the KiCAD files in case anyone is interested.

Interesting. Have you built it? How does it sound?
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Old 8th April 2019, 05:12 AM   #3
kipphebel3 is offline kipphebel3  Aland Islands
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Have not built it yet Wanted to see if I made any obvious mistakes in the layout before ordering PCBs. I intend to measure it after building though.

Last edited by kipphebel3; 8th April 2019 at 05:34 AM.
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Old 8th April 2019, 07:26 AM   #4
blueskynis is offline blueskynis  Serbia
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Yet another LM3886 Layout. Single-supply
Hello, the circuitry around mute seems that it is not properly implemented (particularly I am talking about capacitor C11 position). Even in the datasheet it seems wrong. The best way to see this is if you have a look at internal schematic and symmetrical power supply schematic. The capacitor in that schematic is tied between GND and MUTE pin. They say that you need to draw equal to or more than 0.5mA to turn it on and on symmetrical power supply schematic the capacitor is there to slow down the slope of the current. On single supply schematic the capacitor does exactly the opposite.

In my opinion the capacitor should be tied between Q1 emiter and MUTE pin. In that case, you also must ensure that Q1 Vbe does not get reversed during shutdown because MUTE capacitor may dump the stored energy into this junction.
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Old 8th April 2019, 07:31 AM   #5
kipphebel3 is offline kipphebel3  Aland Islands
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Yes. I thought about that as well, but the schematic in the datasheet says so. Let me try relocating the cap on the prototype and see what happens.
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Old 8th April 2019, 10:21 AM   #6
kipphebel3 is offline kipphebel3  Aland Islands
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Come to think of it.. would it not be better for the cap to be between V+ and mute. Initially it is discharged and no current flows out of the mute pin, but it is slowly charged through Rm and when voltage passes vcc/2 and the diode drops, current starts to flow?
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Old 11th April 2019, 02:35 PM   #7
kipphebel3 is offline kipphebel3  Aland Islands
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Yes. The way it is connected in the datasheet leads to a large current rushing in on powerup, whereas connecting it to the vcc/2 reference does what it is supposed to do:
Attached Images
File Type: jpg lm3886_mute_2019-04-11_17-32-55.jpg (259.6 KB, 495 views)
Attached Files
File Type: asc LM3886_Mute.asc (1.8 KB, 6 views)
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Old 15th April 2019, 05:18 AM   #8
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by kipphebel3 View Post
Comments? I can upload the KiCAD files in case anyone is interested.
Arrgh KICAD !
Excellent for number of library components but full of bugs.
They even admit it on the website especially concerning latest versions.
They seem to let stuff out without properly debugging it.
What do you expect for free though ?
You pay your money and you take your choice.....
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Old 15th April 2019, 05:45 AM   #9
kipphebel3 is offline kipphebel3  Aland Islands
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FWIW, KiCAD is absolutely worth the money
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Old 16th April 2019, 01:45 AM   #10
ICG is offline ICG  Germany
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Location: I had a Déjà Moo - I've seen that BS before!
Quote:
Originally Posted by kipphebel3 View Post
FWIW, KiCAD is absolutely worth the money
Worth the money? It's free, isn't it?
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