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TPA0212 Datasheet(PDF) 24 Page - Texas Instruments |
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TPA0212 Datasheet(HTML) 24 Page - Texas Instruments |
24 / 35 page www.ti.com RL C(C) VO(PP) VO(PP) VDD –3 dB fc SINGLE-ENDED OPERATION BTL AMPLIFIER EFFICIENCY V(LRMS) VO IDD IDD(avg) TPA0212 SLOS284B – NOVEMBER 1999 – REVISED NOVEMBER 2004 Figure 45. Single-Ended Configuration and Frequency Response Increasing power to the load does carry a penalty of increased internal power dissipation. The increased dissipation is understandable considering that the BTL configuration produces 4 × the output power of the SE configuration. Internal dissipation versus output power is discussed further in the Crest Factor and Thermal Considerations Section. In SE mode (see Figure 44 and Figure 45), the load is driven from the primary amplifier output for each channel (OUT+, terminals 21 and 4). The amplifier switches single-ended operation when the SE/BTL terminal is held high. This puts the negative outputs in a high-impedance state, and reduces the amplifier's gain to 1 V/V. Class-AB amplifiers are notoriously inefficient. The primary cause of these inefficiencies is voltage drop across the output stage transistors. There are two components of the internal voltage drop. One is the headroom or dc voltage drop that varies inversely to output power. The second component is due to the sine-wave nature of the output. The total voltage drop can be calculated by subtracting the RMS value of the output voltage from VDD. The internal voltage drop multiplied by the RMS value of the supply current, IDDrms, determines the internal power dissipation of the amplifier. An easy-to-use equation to calculate efficiency starts out as being equal to the ratio of power from the power supply to the power delivered to the load. To accurately calculate the RMS and average values of power in the load and in the amplifier, the current and voltage waveform shapes must first be understood (see Figure 46). Figure 46. Voltage and Current Waveforms for BTL Amplifiers Although the voltages and currents for SE and BTL are sinusoidal in the load, currents from the supply are different between SE and BTL configurations. In an SE application the current waveform is a half-wave rectified shape, whereas in BTL it is a full-wave rectified waveform. This means RMS conversion factors are different. Keep in mind that for most of the waveform both the push and pull transistors are not on at the same time, which supports the fact that each amplifier in the BTL device only draws current from the supply for half the waveform. The following equations are the basis for calculating amplifier efficiency. 24 |
Similar Part No. - TPA0212_07 |
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Similar Description - TPA0212_07 |
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