SLAA719 August   2016 TPA3221 , TPA3244 , TPA3245 , TPA3250 , TPA3251 , TPA3255 , TPA3255-Q1

 

  1.   TPA32xx Analog Input Grounding for Single Ended Inputs
    1.     Trademarks
    2. 1 Single Ended to Differential Input Stage
    3. 2 Input Stage with Ground Plane
      1. 2.1 Testing Ground Plane Configuration
      2. 2.2 Ground Plane Results
    4. 3 Input Stage with Star Ground
      1. 3.1 Testing Star Ground Configuration
    5. 4 TPA32xx Ground Pin Reference

1 Single Ended to Differential Input Stage

Figure 1 shows the basic setup for a Single-Ended (SE) to Differential (Diff) input stage used with the TPA32xx amplifier. In this use case, the amplifier is configured for BTL output and requires “Input_A” and “Input_B” to be driven differentially. A pair of inverting Op-amps is used where the Op-amp gain is set to
–1. By cascading the operational-amplifiers as shown, the analog signal from the RCA jack labeled “SE Input” appears on both “Input_A” and “Input_B” of the TPA32xx amplifier out of phase with each other.

These operational-amplifiers also run from a single 12 V supply rail to reduce cost. In order to pass analog signals that swing below ground, the operational-amplifiers are biased to the mid rail (6 V) using a resistor divider and filter. Then DC blocking capacitors are used to isolate the Op-amp bias voltage from a ground referenced analog input.

This cost effective SE to Diff converter works quite well; however, since this design is not using a truly differential operational-amplifier stage, there will always be some imbalance between “Input_A” and “Input_B” with this configuration and less than ideal common mode (CM) rejection.

figure1_slaa719.gif
Note: Only one channel of TPA32xx Class-D Amplifier is shown
Figure 1. Cost Effective SE to Diff Input Stage