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TAS5704 20-W Stereo Digital Audio Power Amplifier With Feedback TI
Texas Instruments TI
TAS5704 Datasheet PDF : 34 Pages
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TAS5704
SLOS563 – MARCH 2008
www.ti.com
DIFFERENTIAL INPUT AND BTL OUTPUT (TAS5704 Mono Configuration)
Many of the class-D APAs and many class-AB APAs have differential inputs and bridge-tied-load (BTL) outputs.
Differential inputs have two input pins per channel and amplify the difference in voltage between the pins.
Differential inputs reduce the common-mode noise and distortion of the input circuit. BTL is a term commonly
used in audio to describe differential outputs. BTL outputs have two output pins providing voltages that are 180°
out of phase. The load is connected between these pins. This has the added benefits of quadrupling the output
power to the load and eliminating a dc-blocking capacitor.
A block diagram of the measurement circuit is shown in Figure 33. The differential input is a balanced input,
meaning the positive (+) and negative (–) pins have the same impedance to ground. Similarly, the SE output
equates to a balanced output.
Generator
VGEN
RGEN
RGEN
Evaluation Module
Audio Power
Amplifier
CIN
RIN
CIN
RIN
Lfilt
Cfilt
Lfilt
RL
Cfilt
Analyzer
RANA
RANA
CANA
CANA
Twisted-Pair Wire
Twisted-Pair Wire
Figure 33. Differential Input, BTL Output Measurement Circuit
The generator should have balanced outputs, and the signal should be balanced for best results. An unbalanced
output can be used, but it may create a ground loop that affects the measurement accuracy. The analyzer must
also have balanced inputs for the system to be fully balanced, thereby cancelling out any common-mode noise in
the circuit and providing the most accurate measurement.
The following general rules should be followed when connecting to APAs with differential inputs and BTL outputs:
Use a balanced source to supply the input signal.
Use an analyzer with balanced inputs.
Use twisted-pair wire for all connections.
Use shielding when the system environment is noisy.
Ensure that the cables from the power supply to the APA, and from the APA to the load, can handle the large
currents (see Table 6).
Table 6 shows the recommended wire size for the power supply and load cables of the APA system. The real
concern is the dc or ac power loss that occurs as the current flows through the cable. These recommendations
are based on 12-inch (30.5-cm)-long wire with a 20-kHz sine-wave signal at 25°C.
Table 6. Recommended Minimum Wire Size for Power Cables
POUT (W)
10
2
1
< 0.75
RL()
4
4
8
8
AWG Size
18
22
18
22
22
28
22
28
DC POWER LOSS
(mW)
16
40
3.2
8
2
8
1.5
6.1
AC POWER LOSS
(mW)
18
42
3.7
8.5
2.1
8.1
1.6
6.2
28
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