Stereo 3.7W Class D Audio Amplifier Datasheet by Adafruit Industries LLC

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Stereo 3.7W Class D Audio Amplifier
Created by Bill Earl
Last updated on 2018-08-22 03:33:32 PM UTC
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Guide Contents
Guide Contents
Overview
Specifications:
What is a Class D Amplifier?
Other Audio amps available at Adafruit
Assembly
Solder the header:
For breadboard use:
For use with connectors:
And Solder!
Add Gain Selection and Speaker Terminals
Connections and Settings
Inputs:
Outputs:
Gain:
Power:
Build a Portable Sound System
Materials:
Mount The Speakers
Mount the Controls
Wire it up!
Mount the Amplifier
Add some stuffing
Plug And Play!
Downloads
Files
Schematic
PCB Fabrication Print
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 2 of 15
Overview
This incredibly small stereo amplifier is surprisingly powerful - able to deliver 2 x 3.7W channels into 3 ohm impedance
speakers. Inside the miniature chip is a class D controller, able to run from 2.7V-5.5VDC. Since the amp is a class D, its
incredibly efficient (over 90% efficient when driving an 8Ω speaker at over a Watt).
This amplifier is perfect for portable and battery-powered projects. It has built in thermal and over-current protection,
but you really have to drive it hard before it even gets warm! This board is a welcome upgrade to basic "LM386" amps!
Specifications:
Output Power: 3.7W at 3Ω, 10% THD, 1.7W at 8Ω, 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
Differential Inputs
Five pin-selectable gains: 6dB, 9dB, 12dB, 15dB and 18dB. Select with a jumper or by setting the G and G'
breakout pins (see schematic for breakout board showing gain pin settings (https://adafru.it/aWT) for details)
Excellent click-and-pop suppression
Thermal and short-circuit/over-current protection
Low current draw: 2mA quiescent and 10uA in shutdown mode
What is a Class D Amplifier?
A Class D Amplifier uses PWM to generate high-frequency square waves with a duty-cycle proportional to the voltage
level of the input audio signal. By minimizing the transition time between fully on and fully off, the MOSFET drivers are
able to operate at a very high efficiency. Class D amplifiers such as this one typically operate at over 90% efficiency,
compared to efficiencies of 50% or less for typical class AB amplifiers.
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 3 of 15
The high frequency squarerwave component of the output signal is filtered by the inductance ofthe speaker voice coii.
The high frequency square-wave component of the output signal is filtered by the inductance of the speaker voice coil,
leaving only the amplified audio signal.
Other Audio amps available at Adafruit
We have a few choices of audio amplifiers, here's how you can compare them
MAX98306 (http://adafru.it/987) - This class D audio amplifier has selectable gains of 6dB, 9dB, 12dB, 15dB and
18dB that you can choose with a jumper. It can do up to 3.7W into 3Ω, 2.8W into 4Ω and 1.7W into 8Ω. However,
you cannot shut down each speaker separately. Its a good choice where you don't mind setting the gain with a
jumper and if you do not need to ever turn off only one audio channel and you do not need more than 18dB. Its
an excellent amplifier that can driver down to 3Ω speakers
Like the TS2012, it has differential inputs, bridge tied outputs, and can run from 2.7V to 5.5V
TS2012 (http://adafru.it/1552) - This class D audio amplifier has selectable gains of 6dB, 12dB, 18dB and 24dB that
you can choose with a jumper (the MAX98306 goes up to 18dB only). It can do up to 2.8W into 4Ω and 1.7W into
8Ω. It cannot drive 3Ω. You can shut down each channel separately. Setting the gain is easy on the onboard DIP
switches. Its a good choice where you don't need to drive 3Ω speakers or if you ever want to turn off only one
audio channel. If you need 24dB gain this amp can do it.
Like the MAX98306, it has differential inputs, bridge tied outputs, and can run from 2.7V to 5.5V
Available from Adafruit! (http://adafru.it/987)
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 4 of 15
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Assembly
The amplifier breakout board is fully assembled and tested. To easily integrate the amplifier into your project, we
include the following:
A 9-pin header for use with breadboard or connectors
3.5mm screw-terminal blocks for your speakers
A 2x4 header + jumper for setting the gain
Solder the header:
Cut the header to size (9 pins) and insert it into a
breadboard (long pins down!) to hold it steady.
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 5 of 15
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For breadboard use:
Place the amplifier module face-up over the headers.
Prop the back-edge up with the leftover header strip to
align it.
For use with connectors:
If you are going to build this into a project and want to
connect from the front side, place the amplifier module
face down for soldering.
And Solder!
For tips on soldering, see our Adafruit Guide to Excellent
Soldering. (https://adafru.it/aTk)
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 6 of 15
Add Gain Selection and Speaker Terminals
Solder the 2x4 pin header for gain selection to the top
of the board as shown. Also solder in the 3.5mm screw
terminals for the speakers.
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 7 of 15
Connections and Settings
Inputs:
The amplifier inputs are coupled via 1.0uF capacitors so
they can handle single ended or differential signals.
For Single Ended signals (shown on left), connect:
R+ to R+
GND to R-
L+ to L+
GND to L-
For differential signals, connect:
R+ to R+
R- to R-
L+ to L+
L- to L-
For volume control, a dual 50K audio taper pot can be
wired in series with the inputs as shown.
Outputs:
This amplifier is designed to drive moving coil
loudpeakers only. Speaker impedence must be 3ohms
or more. The output signal is a 360KHz 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 of the
two channels, the + and - alternate polarity to create a
single channel amplifier with twice the available power.
However, that means you cannot bridge R and L
together, so don't try to connect ROUT to LOUT, it will
damage the amp! If you only need one speaker, just
connect to either ROUT
or
LOUT and leave the other
output set alone
Connect your speakers using the 3.5mm screw-terminal
blocks.
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 8 of 15
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Gain:
Gain is configurable for 9, 12, 15 or 18 dB. For higher
level outputs such as from a WaveShield, you will want
to select a lower gain. For low-level outputs such as
from an iPod or MP3 player, a higher gain setting works
best. To set the gain, install the jumper in one of the 4
marked positions on the 4x2 header.
Power:
The amplifier can be powered by 2.7 to 5.5v DC. Good
power sources are:
5v 2A power supply (http://adafru.it/276)
3xAA (4.5v) battery holder (http://adafru.it/771)
Connect the negative wire to GND and the positive wire
to VDD.
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 9 of 15
Build a Portable Sound System
Materials:
To build a portable sound system, you will need:
1 Adafruit Stereo Class-D Amplifier (http://adafru.it/987)
2 speakers (3 ohm minimum. 3" to 4" is a good size)
1 3xAA Battery Pack (http://adafru.it/771)
1 Power Switch (http://adafru.it/482)
1 Phono Jack (We used a 1/4" here)
1 50kOhm Stereo Audio-taper pot
1 knob
Jumper wires (http://adafru.it/266)
1 Box (We used the case from a power tool. But any lunch-box sized enclosure will work as well)
2 Speaker Grilles (We used some 4" fan grilles here)
Screws & nuts to mount the speakers.
Polyester batting or pillow stuffing
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 10 of 15
Mount The Speakers
Cut holes in the box to fit your speakers and mount
them in the box with screws. Here we used 4" speakers
with 4" fan grilles and mounted them with 3/4" 6-32
machine screws and nuts.
Mount the Controls
Drill holes to fit your power switch, volume pot and
phono jack in a convenient location and mount the
controls.
Here we used a 1/4" phono jack. Smaller plugs can be
accomodated via adapters. Our volume pot has a Spinal-
Tap compliant volume scale that "goes to eleven".
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 11 of 15
Wire it up!
Make all connections as shown on the diagram to the
left. We used these pre-terminated jumper
wires (http://adafru.it/266) to simplify connections to the
amplifier.
Mount the Amplifier
Some double-sided foam tape will hold it securely inside
the box.
Add some stuffing
Loosely stuff the back of the box with some polyester
batting or pillow stuffing for a less 'hollow' sound.
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 12 of 15
Plug And Play!
For an iPod or similar player, you will want to use the
highest gain setting.
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 13 of 15
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Downloads
Files
MAX98306 Datasheet (https://adafru.it/e7o)
Fritzing object in Adafruit Fritzing library (https://adafru.it/aP3)
EagleCAD PCB files on GitHub (https://adafru.it/rJc)
Schematic
PCB Fabrication Print
Dimensions in inches
© Adafruit Industries https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier Page 14 of 15
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© Adafruit Industries Last Updated: 2018-08-22 03:33:27 PM UTC Page 15 of 15

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