TPA741_15 Datasheet, PDF(12/28 Page) Texas Instruments – 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS

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TPA741_15 Datasheet, PDF (12/28 Pages) Texas Instruments – 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS

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TPA741

SLOS316C â JUNE 2000 â REVISED JUNE 2004

APPLICATION INFORMATION (continued)

VDD

VO(PP)

â3 dB

www.ti.com

Figure 24. 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 4Ã the output power of a SE

configuration. Internal dissipation versus output power is discussed further in the thermal considerations section.

BTL AMPLIFIER EFFICIENCY

Linear 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 being equal to the ratio of power from the power supply

to the power delivered to the load. To accurately calculate the RMS values of power in the load and in the

amplifier, the current and voltage waveform shapes must first be understood (see Figure 25).

IDD

VL(RMS)

IDD(RMS)

Figure 25. 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.

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