參數(shù)資料
型號: TPA0222PWP
廠商: Texas Instruments, Inc.
元件分類: 音頻放大器
英文描述: STEREO 2-W AUDIO POWER AMPLIFIER WITH FOUR SELECTABLE GAIN SETTINGS AND MUX CONTROL
中文描述: 立體聲2 - W音頻功率放大器,具有四種可選增益設(shè)置和MUX控制
文件頁數(shù): 26/33頁
文件大?。?/td> 522K
代理商: TPA0222PWP
TPA0222
STEREO 2-W AUDIO POWER AMPLIFIER
WITH FOUR SELECTABLE GAIN SETTINGS AND MUX CONTROL
SLOS285 – NOVEMBER 1999
26
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
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
considerationssection.
single-ended operation
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.
input MUX operation
The input MUX allows two separate inputs to be applied to the amplifier. This allows the designer to choose
which input is active independent of the state of the SE/BTL terminal. When the HP/LINE terminal is held high,
the headphone inputs are active. When the HP/LINE terminal is held low, the line BTL inputs are active.
BTL amplifier efficiency
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 sinewave nature of
the output. The total voltage drop can be calculated by subtracting the RMS value of the output voltage from
V
DD
. The internal voltage drop multiplied by the RMS value of the supply current, I
DD
rms, 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).
V(LRMS)
VO
IDD
IDD(avg)
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 very
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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