The MAX98357A is an I2S amplifier - it does not use analog inputs, it only has digital audio input support! Don't confuse I2S with I2C, I2S is a sound protocol whereas I2C is for small amounts of data.

Power Pins

• Vin - This is the power for the amplifier and logic of the amplifier. You can provide 2.5V to 5.5V. Note that at 5V you can end up putting up to 2.8W into your speaker, so make sure your power supply can easily handle up to 650mA. We recommend a power supply spec'd for at least 800mA to give yourself some 'room'. If you have a 3.3V logic device, you can still power the amp from 5V, and that's recommended to get the most power output!
• GND - common ground for power and logic

I2S Pins

Three pins are used to receive audio data. These can be 3.3-5V logic

• BCLK (Bit Clock) - This is the pin that tells the amplifier when to read data on the data pin.
• LRC (Left/Right Clock) - this is the pin that tells the amplifier when the data is for the left channel and when its for the right channel
• DIN (Data In) - This is the pin that has the actual data coming in, both left and right data are sent on this pin, the LRC pin indicates when left or right is being transmitted

Note that this amplifier does not require an MCLK pin, if you have an MCLK output, you can leave it disconnected!

Speaker Outputs

• RIGHT +/- and LEFT +/- - At the top edge of the board are two sets of terminal block speaker outputs. Each terminal block (LEFT and RIGHT) are each connected to their own MAX98357A. The LEFT output outputs the left channel and the RIGHT output outputs the right channel.

These amplifiers are designed to drive moving coil loudspeakers only. Speaker impedance must be 4Ω or more. The output signal is a 330KHz PWM square wave with a duty cycle proportional to the audio signal. The inductance of the speaker coil serves as a low-pass filter to average out the high-frequency components. Do not try to use this as a pre-amplifier.

The outputs of each channel are "Bridge-Tied" with no connection to ground. This means that for each channel, the + and - alternate polarity to create a single channel amplifier with twice the available power. 

Connect your speakers using the 3.5mm screw-terminal blocks.

• 5V into 4Ω @ 10% THD - 3W max
• 5V into 4Ω @ 1% THD - 2.5W max
• 3.3V into 4Ω @ 10% THD - 1.3W max
• 3.3V into 4Ω @ 1% THD - 1.0W max

• 5V into 8Ω @ 10% THD - 1.8W max
• 5V into 8Ω @ 1% THD - 1.4W max
• 3.3V into 8Ω @ 10% THD - 0.8W max
• 3.3V into 8Ω @ 1% THD - 0.6W max

Close for 3V Jumper

On the back of the board is a jumper labeled Close for 3V. This jumper is connected to the SD_MODE pin on the right speaker's MAX98357A. If you are powering the board with 3V, you'll want to solder this jumper closed to continue having that MAX98357A output the right channel audio. Otherwise the voltage drops too low and both left and right channels will output through that MAX98357A.

Gain Pin and Gain Jumpers

The default gain is 9dB, but you can easily change it by tweaking the connection to the GAIN pin or soldering the jumpers on the front of the board. Note you may need to perform a power reset to adjust the gain.

• GAIN - gain setting pin. You can have a gain of 3dB, 6dB, 9dB, 12dB or 15dB.
  • 15dB if a 100K resistor is connected between GAIN and GND
  • 12dB if GAIN is connected directly to GND
  • 9dB if GAIN is not connected to anything (this is the default)
  • 6dB if GAIN is connected directly to Vin
  • 3dB if a 100K resistor is connected between GAIN and Vin
• Gain jumpers - on the front of the board are three jumper pads labeled 3, 9 and 15. If solder 3 and 9 closed, it sets the gain to 3dB. If you solder 15 and 9 closed, it sets the gain to 15dB.