Texas Instruments SLOU025 manual 3.2.2Module Gain, 3.2.3Shutdown, Details

The TPA122 MSOP Audio Power Amplifier Evaluation Module

3.2.2Module Gain

The TPA122 MSOP evaluation module has a set gain of 4 (inverting) for each channel. However, the gain can be adjusted to a maximum of approximately 10 (inverting) by changing the value of feedback resistors (R2 and R4, Figure 3±3). Use the following equation to determine the value of RF:

Gain +± RF

RI

The TPA122 amplifier IC, like most other amplifiers, exhibits its best distortion and noise performance at lower gain levels. In addition, higher gain levels require a small compensation capacitor to ensure stability (see the TPA122 data sheet).

Gain versus total harmonic distortion (THD) and gain versus signal-to-noise ratio (SNR) should be considered in each application. Both the module input signal level and the TPA122 MSOP 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 TPA122 input, and the TPA122 gain should be kept as low as possible.

3.2.3Shutdown

When the shutdown terminal of the TPA122 amplifier IC is taken high, the IC ceases operation and enters a very low power state (65 μA at VDD = 5 V and 10 μA at VDD = 3.3 V Typ). This is accomplished by applying a control signal to the module SD 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 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 (JP7).

Details 3-5