Class D amplifier has been very popular recently. They are smaller, lighter and very efficient which is very well suited for battery operation. They also require smaller heatsinks than their class A and AB counter parts. This enables you to fit it in a smaller chassis. It also gives more power because the output is normally configured like bridge tied. The only disadvantage of Class D amplifier is that it has higher THD(Total Harmonic Distortion) than its class A and AB counter parts. This is not a problem if you will not operate it on the maximum power.
Circuit
The circuit is simple but for higher power, it will require an inductor at the output which is not easy to find on your local electronic parts store. Unlike the other class A and AB amplifiers, setting the gain is not as easy as changing the feedback resistor. But it is not hard to do, you will just need to set a particular pin to high or low. This will give you very limited gain combination, but it is not an issue because audio amplifiers need no high gain.
Bridge option
You have the option to bridge the 2 channel to get more power for a single channel application such as sub-woofer.
Also Read: 200W class D amplifier