The TPA311 Audio Power Amplifier Evaluation Module
3.2.3SIngle-Ended Operation
For single-ended operation, the module SE/BTL control input pin must be held high. The speaker (or headphone) load is connected to the module OUT+ output pin through a coupling capacitor, and to platform/system ground. A 470 -∝F electrolytic coupling capacitor is provided on the platform in the signal path to the headphone output jack for this purpose and a control signal from the platform headphone jack can be routed to the module control input pin to switch the TPA311 IC to the single-ended mode.
In the single-ended mode, the amplifier inside the TPA311 IC that drives the OUT± line does not operate and does not dissipate any power. The OUT± pin goes into a high-impedance state and can be left connected or allowed to float.
3.2.4Module Gain
The TPA311 evaluation module can be set for an overall gain of between 2 and 22 by adjustment of the the on-board gain control, R4. The TPA311 amplifier IC, as most other amplifiers, exhibits its best distortion and noise performance at lower gain levels (see the TPA311 data sheet). Even so, the TPA311 at its highest gain setting has significantly less distortion than most low-cost speakers.
Gain versus total harmonic distortion (THD) should be considered in each application. Both the module input signal level and the TPA311 module gain should be adjusted to obtain the lowest overall distortion level for a particular overall gain. A quick rule of thumb (everything else being equal): the module input signal level should be as high as possible without clipping or overloading the TPA311 input, and the TPA311 gain kept as low as possible.
3.2.5Shutdown
When the shutdown terminal of the TPA311 amplifier IC is taken high, the IC ceases operation and enters an ultra-low power state. This is accomplished by applying a control signal to the module Shutdown pin or by pressing the Shutdown switch, S1, on the module. When the control signal goes low or is removed (or the switch is released), amplifier operation resumes.
The Plug-N-Play platform can generate the shutdown (mute) signal for the module either when a plug is inserted into the platform headphone output jack or when the plug is removed, as selected by a platform jumper (JP8).
