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TPA3122D2 Datasheet(PDF) 10 Page - Texas Instruments |
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TPA3122D2 Datasheet(HTML) 10 Page - Texas Instruments |
10 / 22 page www.ti.com APPLICATION INFORMATION CLASS-D OPERATION Traditional Class-D Modulation Scheme 0V 0V -12V -12V +12V +12V Current OUTP DifferentialVoltage AcrossLoad OUTN 0V Supply Pumping Gain setting via GAIN0 and GAIN1 inputs TPA3122D2 SLOS527A – DECEMBER 2007 – REVISED DECEMBER 2007 This section focuses on the class-D operation of the TPA3122D2. The TPA3122D2 operates in AD mode. There are two main configurations that may be used. For stereo operation, the TPA3122D2 should be configured in a single-ended (SE) half bridge amplifier. For mono applications, TPA3122D2 may be used as a bridge tied load (BTL) amplifier. The traditional class-D modulation scheme, which is used in the TPA3122D2 BTL configuration, has a differential output where each output is 180 degrees out of phase and changes from ground to the supply voltage, VCC. Therefore, the differential pre-filtered output varies between positive and negative VCC, where filtered 50% duty cycle yields 0 V across the load. The traditional class-D modulation scheme with voltage and current waveforms is shown in Figure 25. Figure 25. Traditional Class-D Modulation Scheme's Output Voltage and Current Waveforms into an Inductive Load With No Input One issue encountered in single-ended (SE) class-D amplifier designs is supply pumping. Power-supply pumping is a rise in the local supply voltage due to energy being driven back to the supply by operation of the class-D amplifier. This phenomenon is most evident at low audio frequencies and when both channels are operating at the same frequency and phase. At low levels, power-supply pumping results in distortion in the audio output due to fluctuations in supply voltage. At higher levels, pumping can cause the overvoltage protection to operate, which temporarily shuts down the audio output. Several things can be done to relieve power-supply pumping. The lowest impact is to operate the two inputs out of phase 180 ° and reverse the speaker connections. Because most audio is highly correlated, this causes the supply pumping to be out of phase and not as severe. If this is not enough, the amount of bulk capacitance on the supply must be increased. Also, improvement is realized by hooking other supplies to this node, thereby, sinking some of the excess current. Power-supply pumping should be tested by operating the amplifier at low frequencies and high output levels. The gain of the TPA3122D2 is set by two input terminals, GAIN0 and GAIN1. The gains listed in Table 1 are realized by changing the taps on the input resistors and feedback resistors inside the amplifier. This causes the input impedance (ZI) to be dependent on the gain setting. The actual gain settings are controlled by ratios of resistors, so the gain variation from part-to-part is small. However, the input impedance from part-to-part at the same gain may shift by ±20% due to shifts in the actual resistance of the input resistors. 10 Submit Documentation Feedback Copyright © 2007, Texas Instruments Incorporated Product Folder Link(s) :TPA3122D2 |
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