Output Power
We measured the output power of the two amplifiers with 4Ω resistors connected to the outputs. The ADAU1701 created a 1 kHz sine-wave with different amplitudes. We also used a thermal camera to check the thermal characteristics. Unfortunately, we implemented a fuse (F1) with a too low hold current, so it turned the whole board off as soon as we reached a certain input power. This bug is fixed in the version you can download.
The output power is lower than the input power due to the power consumption of all the components on the board and power losses.
| Input Voltage /V | Input Power /W | Output Power RMS /W |
|---|---|---|
| 12 | 1.8 | 0.3 |
| 12 | 5.5 | 3.1 |
In the following thermal images you can see that at first the ADAU is the hottest part, but as soon as you draw more power out of the two amps, they quickly become the hot spots on the board.
Thermal distribution at 0.3W output:
Thermal distribution at 3.1W output:
After removing the fuse, we only used the output of Speaker 2 A with a 4Ω resistor as load. As stated before, it is better to use a higher supply voltage to drive the speakers or in this case the resistor, so we changed the voltage to 20V.
| Input Voltage /V | Input Power /W | Output Power RMS /W |
|---|---|---|
| 20 | 11.6 | 7.5 |
| 20 | 16.9 | 11.6 |
| 20 | 21.0 | 14.7 |
| 20 | 23.8 | 16.5 |
The amplifier IC handled the high power really well. Thanks to our thermal design, the heat is distributed over a larger area and the bottom of the PCB is also used as a heat spreader.
Thermal distribution at 11.6W:
Thermal distribution at 11.6W, bottom:
After several minutes at 14,7W, the amp had a temperature of 117°C. This is very hot, but the IC managed to keep a constant output power. We then pushed the amplifier to its limits and forced a thermal shutdown, which happened at around 140°C. As you can see, all other components stayed at an acceptable operating temperature. After the thermal shutdown, the amplifier quickly recovered, did not take any damage and worked as before. It is not recommended to force this situation on your board, but if it happens, you will have to unplug it from any power supply and then restart it.
Thermal distribution at 16.5W:
