Adafruit Stereo 3.7W Class D Audio Amplifier

A small but surprisingly powerful stereo amplifier with selectable gain:

• Delivers 2 x 3.7W channels in to 3 ohm impedance speakers
• Class D controller able to run from 2.7V-5.5V DC
• Incredibly efficient - over 90% efficient when driving an 8 ohm speaker at over a Watt
• Output Power: 3.7W at 3?, 10% THD, 1.7W at 8?, 10% THD, with 5V Supply
• Passes EMI limit unfiltered with up to 12 inches (30 cm) of speaker cable
• High 83dB PSRR at 217Hz
• Spread-Spectrum Modulation and Active Emissions Limiting
• Five pin-selectable gains: 6dB, 9dB, 12dB, 15dB and 18dB. Select with a jumper or by setting the G and G' breakout pins (see the schematic for breakout board showing gain pin settings for details)
• Excellent click-and-pop suppression
• Thermal and short-circuit/over-current protection
• Low current draw: 2mA quiescent and 10uA in shutdown mode
• Dimensions - 23.28mm (l) x 24.15mm (w) x 3.03mm (h)

The inputs of the amplifier go through 1.0uF capacitors, so they are fully 'differential' - if you don't have differential outputs, simply tie the R- and L- to ground. The outputs are "Bridge Tied" - that means they connect directly to the outputs, no connection to ground. The output is a 360KHz square wave PWM that is then 'averaged out' by the speaker coil - the high frequencies are not heard. All the above means that you can't connect the output into another amplifier, it should drive the speakers directly.