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Old 15th November 2012, 07:11 AM   #1
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Default Battery powered audio amp

Hi everyone.

I am looking for a simple (small external component count) class D audio amplifier which will run off a 9.6V NIMH battery pack. I chose the class D technology because of its high efficiency. It just needs to have one channel and the output power should be around 15W to 20W into 4Ohms at 9.6V supply voltage. Also it would be nice if the chip was easy to solder, i.e. no pads underneath the package.

Does anyone of you know a suitable amplifier for me? I have already searched several silicon manufacturers, but none of them seems to have what I am looking for, so I am counting on you now

Best regards,
Sven
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Old 15th November 2012, 08:03 AM   #2
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The TI design tool points to the TPA3112D1.
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Old 15th November 2012, 08:53 AM   #3
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Unfortunately that package does have a thermal pad underneath. Additionally I am not sure for how long that system would work, since the specified minimal voltage is 8V.
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Old 15th November 2012, 09:17 AM   #4
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1a. Use some PCB copper as heatsink.
1b. Memory tells me the NiMH discharge is fairly flat, with a steeper drop when capacity is exhausted.
2. Reduce your output requirements so you can use a ~6-12V rated chip.

edit: Panasonic's NiMH docs show the flat-ish discharge.
You don't want to discharge your battery below 8V (1V/cell) in any case.
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Last edited by sofaspud; 15th November 2012 at 09:39 AM.
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Old 15th November 2012, 09:59 AM   #5
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re: 1a
You can leave plenty of copper under the chip. Drill a few holes large enough for your soldering iron tip. To attach the chip, spot solder two corners of the chip to align it with the topside pads. Turn the board over (and possibly applying a bit of pressure to meet the board to the thermal pad) and apply solder through the holes you drilled earlier. The solder will flow well across the pad. Remember, you will be running the chip at the lower end of its power rating, so there's no need to go "all out" on the thermal pad.
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