# Options for class D amp using Power over Ethernet

I'm putting together a design for a small amplifier that utilises power over Ethernet (PoE). The design specifications are:

• 10w to 30w (as long as >10w power isn't critical)

• 56v asymmetrical power (0v, +56v)

• Stereo in 1 package

• current available only 0.6a (due to PoE specs 802.3at)

• high efficiency (hence class-D)

• Audio quality not that critical (does not need to be audiophile)

• small package with low BoM count

• $5 -$8 per chip in medium volume

• I2S input ideally but will take analogue instead

Spending time searching the usual suspects (TI, NXP etc.) seems its difficult to find higher voltage class D chips as they are typically meant for high power amps and also are higher cost or complex (eg. the TI TAS56xx range) with fairly low efficiency at lower power for class D. The simpler chips more suited to my application are all lower voltage, typically 24 - 36v. I'm also obviously constrained with current although a decent electro on the power supply with provide much higher 'peak music power'.

My questions:

1) Anyone know of any chip that may be suitable that I may have missed?

2) There are a couple of chips that are in this voltage range but require symmetrical power (+- 28v) however I'm not sure if they can be tricked into running on symmetrical power 0v, +56v) without running in bridge mode which turns them into mono amps. Any tips on how to do this (eg. TDA8922 is a candidate)

3) the Ti TAS56xx chips would be somewhat suitable (price and efficiency not great) if they could use a slightly higher voltage. 56v is within the absolute maximum voltage specification but obviously I'm nervous running them a little bit outside their recommended maximum voltage.

I'm considering using a buck regulator to drop the voltage however this adds complexity, size and lowers efficiency.

Any ideas greatly appreciated.

• 30W is easily reachable at lower voltages using a bridged configuration; using full voltage can give you over 100W into a speaker. Nov 20 '14 at 22:28
• Yes, but my problem is locating a suitable class D IC that can use 56v with reasonable efficiency / cost that will run typically at 5w - 15w (due to current restrictions) Nov 20 '14 at 22:31
• Tip: Using a buck regulator will drop the voltage, but also increase the current. Halve the voltage, and you can almost double the current. Nov 20 '14 at 22:45
• Yes, I know, but typically lose 20% efficiency + the extra complexity, cost and size is a constraint. I have a strict power budget at 20W and need to power a processor and other peripherals for the rest of the design. Nov 20 '14 at 22:48
• What if you create a suitable virtual ground so that you can pretend to have +-30V? Does it really have to be class D? Oct 19 '15 at 12:26