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Old 11th July 2011, 06:10 PM   #1
BlaSe is offline BlaSe  Austria
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Default 8 Channel Class D Project TPA3122

Hi,

I'm working on a Board that should hold 4 of the TPA3122's in Stereo mode to power a speaker array. (multible boards are used to get a 4x4 or even bigger array)
I have finished the layout in eagle and I have some questions.

1. Is it allowed to sum the voltage stabilization caps to one or two bigger ones when having 4 of the amps on a small board?

2. Because of the limitations of the free Eagle version i am limited in space, so the GND that connects the components farthest from the supply have only a thin connection. Is that bad? ( I thouth about using a wire to strengthen the connection)

3. The board will actually be produced by a PCB manufacturer.
Can anybody see obvious errors on the board.
DRC only gives ma some stop mask errors.

Thanks for the help.
regards
Sebastian
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Old 12th July 2011, 03:47 AM   #2
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You're going to run into problems with heterodyning of the carrier frequencies through the rails with 4 chips. Even completely decoupling the power supply won't get you interference free output. You would need to have 4 separate power supplies and each amp isolated.

A better solution is to use 8x TPA3106D1 which can be used in a master/slave configuration for the oscillators. If you are limited in space, I'd go with one chip per board, jumpers for the master/slave oscillator links through twisted pair wires, use a single smaller local power supply cap, wide power traces, and a single PS board with big reservoir caps.
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Old 12th July 2011, 04:47 AM   #3
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Two large supply caps is a bad idea IMO. You need two per IC as close to the supply pins as possible. 4x 3122 on the same board is probably a bad idea as well.

I recently finished making a layout for 4x TPA3106D1 (synced) for use in my car. Just need to find time to make the board.
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Old 12th July 2011, 04:01 PM   #4
BlaSe is offline BlaSe  Austria
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Quote:
Originally Posted by killerbobjr View Post
Even completely decoupling the power supply won't get you interference free output.
how strong would that interferences be?
i'm not planing on getting the maximum power/volume out of the amps and i'm using very small speakers.
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Old 13th July 2011, 05:03 AM   #5
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If the frequency was in the audible range, you would constantly hear a tone or tones that won't go away. Do a search in this forum. There was another member who ran into this problem with two TPA3xxx parts on a board where he describes what he encountered.
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Old 17th September 2011, 11:33 AM   #6
BlaSe is offline BlaSe  Austria
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Update:
Despite your warnings i built the thing....and see there. No Problems at all.
Works quite well with a simple switching power supply from a external harddrive.
Click the image to open in full size.
So don't fear putting more than one Amp of this kind on one board.
Regards
S
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