Texas Instruments TPA3008D2 DIFFERENTIAL INPUT AND BTL OUTPUT

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Analyzer

20 Hz − 20 kHz

(a) Basic Class−AB

APA

Signal

Generator

Power Supply

Analyzer

20 Hz − 20 kHz

RL

(b) Filter-Free and Traditional Class-D

Class-D APA

Signal

Generator

Power Supply

RL

Low-Pass RC

Filter

Low-Pass RC

Filter

(A)

(A) For ef ficiency measurements with filter-free class-D, RL should be an inductive load like a speaker.

DIFFERENTIAL INPUT AND BTL OUTPUT

TPA3008D2

SLOS435A – MAY 2004 – REVISED JULY 2004

Figure 21. Audio Measurement Systems

The TPA3008D2 uses a modulation scheme that does not require an output filter for operation, but they dosometimes require an RC low-pass filter when making measurements. This is because some analyzer inputscannot accurately process the rapidly changing square-wave output and therefore record an extremely high levelof distortion. The RC low-pass measurement filter is used to remove the modulated waveforms so the analyzercan measure the output sine wave.

All 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 commonlyused in audio to describe differential outputs. BTL outputs have two output pins providing voltages that are 180degrees out of phase. The load is connected between these pins. This has the added benefits of quadrupling theoutput power to the load and eliminating a dc blocking capacitor.

A block diagram of the measurement circuit is shown in Figure 22 . The differential input is a balanced input,meaning the positive (+) and negative (-) pins have the same impedance to ground. Similarly, the BTL outputequates to a balanced output.

21

Contents

Main www.ti.com FEATURES DESCRIPTION Copyright 2004, Texas Instruments Incorporated 10-W STEREO CLASS-D AUDIO POWER AMPLIFIER PRODUCTION DATA information is current as of publication date. ABSOLUTE MAXIMUM RATINGS DISSIPATION RATING TABLE RECOMMENDED OPERATING CONDITIONS TPA3008D2 over operating free-air temperature range (unless otherwise noted) = 25C (unless otherwise noted) AVAILABLE OPTIONS DC ELECTRICAL CHARACTERISTICS TPA3008D2 = 25C, V = 12 V, R = 8 (unless otherwise noted) = 25C, V FUNCTIONAL BLOCK DIAGRAM TPA3008D2 TERMINAL FUNCTIONS TYPICAL CHARACTERISTICS TABLE OF GRAPHS TPA3008D2 TOTAL HARMONIC DISTORTION + NOISE TOTAL HARMONIC DISTORTION + NOISEvs vsFREQUENCY FREQUENCY Figure 5. Figure 6. OUTPUT POWER vsCLOSED-LOOP RESPONSE SUPPLY VOLTAGE Figure 7. Figure 8. OUTPUT POWER EFFICIENCYvs vsSUPPLY VOLTAGE OUTPUT POWER Figure 9. Figure 10. EFFICIENCY SUPPLY CURRENTvs vsTOTAL OUTPUT POWER TOTAL OUTPUT POWER Figure 11. Figure 12. CROSSTALK SUPPLY RIPPLE REJECTION RATIOvs vsFREQUENCY FREQUENCY Figure 13. Figure 14. COMMON-MODE REJECTION RATIOvsFREQUENCY Figure 15. APPLICATION INFORMATION Figure 16. Stereo Class-D With Differential Inputs CLASS-D OPERATION Traditional Class-D Modulation Scheme TPA3008D2 Modulation Scheme Efficiency: LC Filter Required With the Traditional Class-D Modulation Scheme Effects of Applying a Square Wave Into a Speaker When to Use an Output Filter for EMI Suppression RLrds(on)100% 8 Gain setting via GAIN0 and GAIN1 inputs INPUT RESISTANCE Figure 19. Typical LC Output Filter, Cutoff Frequency of 27 kHz, Speaker Impedance = 8 INPUT CAPACITOR, C SHUTDOWN OPERATION USING LOW-ESR CAPACITORS SHORT-CIRCUIT PROTECTION AND AUTOMATIC RECOVERY FEATURE THERMAL PROTECTION PRINTED-CIRCUIT BOARD (PCB) LAYOUT BASIC MEASUREMENT SYSTEM DIFFERENTIAL INPUT AND BTL OUTPUT CLASS-D RC LOW-PASS FILTER Page Page PACKAGING INFORMATION PACKAGE OPTION ADDENDUM TAPE AND REEL BOX INFORMATION PACKAGE MATERIALS INFORMATION Page Page Page Page IMPORTANT NOTICE