TPA6120A2_15 Datasheet, PDF (15/31 Pages) Texas Instruments – TPA6120A2 High Fidelity Headphone Amplifier

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TPA6120A2
SLOS431B – MARCH 2004 – REVISED FEBRUARY 2015
10.2.2.1 Design Requirements
• ±5V Operation from an over system power supply of 3.3V
• Stereo differential inputs (DAC is differential)
• Be transparent to the user. (DAC SNR and THD+N performance all the way to the headphone)
10.2.2.2 Detailed Design Procedure
For optimal performance, the TPA6120A2 is configured for use with differential inputs, stereo use, and a gain of
1V/V.
The TPA6120A2 requires a bipolar power supply to drive a ground centered output. The application employs a
TPS65135 DC-DC converter that generates ±5V from a single 3.3V supply.
The PCM5242 DAC is configured for a 1VRMS output so that clipping is avoided should the 3.3V power supply
sag. The PCM5242 offers a ground centered output, so that no DC blocking capacitors are required between it
and the TPA6120A2.
Resistor values around the TPA6120A2 of 806Ω and a 39.2Ω were found to offer the optimal conditions of SNR
and THD. Starting with 1KΩ resistors for input and feedback, and 10Ω output resistance, the feedback resistance
was lowered to increase the amount of current in the feedback network. The output resistance was increased to
ease the load on the headphone amplifier when low impedance headphones are connected. Both of these
additions contribute to the excellent SNR and THD of the TPA6120A2 in such a low voltage application.
Note that the 0.1-uF X7R capacitors are placed at every supply pin of the TPA6120A2.
Using such a solution makes the TPA6120A2 transparent in the circuit, even into a low impedance 32Ohm load.
The remaining steps are the same as those described in Resistor Values.
10.2.2.3 Application Performance Plots
1.20
1.10
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
0
Vcc = +/- 5 V; RL = 32
Vcc = +/- 5 V; RL = 64
Vcc = +/- 15 V; RL = 32
Vcc = +/- 15 V; RL = 64
5 10 15 20 25 30 35 40 45 50
Po - Total Output Power - mW
C009
Figure 20. Power Dissipation versus Power Output - 50mW Scale
In this particular application, the TPA6120A2's performance is transparent and the performance of the system is
dictated by the PCM5242 DAC.
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