ST AN4015 APPLICATION NOTE

AN4015

Application note

Dual-BTL class-D audio amplifier demonstration board

based on the TDA7498E

Introduction

The purpose of this application note is to describe:

■ how to connect the TDA7498 demonstration board

■ how to evaluate the performance of the demonstration board using the electrical curves

■ how to avoid critical issues in the PCB schematic and layout of the TDA7498E

The TDA7498E represents a new generation of analog input class-D devices from STMicroelectronics and is housed in a PSSO36 package. It is able to deliver 160 W +160 W in stereo configuration with V

Figure 1. TDA7498E demonstration board

= 36 V and a 4 Ω load

(a)

a. All of the results and graphs included in this document are measured using Audio Precision equipment.

January 2012 Doc ID 022507 Rev 1 1/22

www.st.com

Contents AN4015

Contents

1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Test conditions and connections of the demonstration board . . . . . . . 5

2.1 Power supply and interface connection . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2 Output configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.3 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3 Schematic diagram and PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5 Test curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

6 Design guidelines for PCB schematic and layout . . . . . . . . . . . . . . . . 14

6.1 Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.1.1 Main driver for the selection of components . . . . . . . . . . . . . . . . . . . . . 14

6.1.2 Decoupling capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.1.3 Output filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.2 Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

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AN4015 List of figures

List of figures

Figure 1. TDA7498E demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. TDA7498E demonstration board connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 3. TDA7498E schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 4. PCB layout - top side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 5. PCB layout - bottom side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 6. PCB layout - top and bottom sides plus components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 7. THD+N vs. power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 8. THD+N vs. frequency (ref = 1 W at 1 kHz) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 9. DNR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 10. FFT (0 dBr at 1 W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 11. Crosstalk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 12. Linearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 13. Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 14. Pout vs. V

Figure 15. Snubber filter - solution 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 16. Snubber filter - solution 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 17. Dumping network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 18. Frequency shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 19. Decoupling capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 20. Snubber network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 21. V

Figure 22. ROSC - component placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 23. Filter capacitors for SVR, VREF, SVCC, VSS and VDDPW. . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 24. Input signal routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 25. Signal ground and power ground routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

decoupling electrolytic capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

and THD level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Doc ID 022507 Rev 1 3/22

Overview AN4015

1 Overview

The following terms used in this application note are defined as follows:

● THD+N vs. Pout: Total Harmonic Distortion (THD) plus noise versus output power

● THD+N vs. Freq: Total Harmonic Distortion plus noise versus frequency curve

● S/N Ratio: Signal-to-noise ratio

● DNR: Dynamic range

● FFT: Fast Fourier Transform Algorithm (method)

● XTalk: Channel separation L to R, or R to L channel crosstalk

The equipment used includes the following:

● Audio Precision 2722A + AES-17 filter + DCX+ AUX-0025 filter

● DC power supply

● Digital oscilloscope (Tektronix TDS5054B)

● Differential voltage probe (LeCroy AP031)

● Current probe (Tektronix TCP300)

Reference documents include:

● TDA7498E datasheet

● Schematic diagram

● PCB layout

● Te s t c u r ves

4/22 Doc ID 022507 Rev 1

AN4015 Test conditions and connections of the demonstration board

2 Test conditions and connections of the

demonstration board

2.1 Power supply and interface connection

1. Connect PSU to the VCC terminal block

2. Connect the analog input cable to the RCA connectors on the demonstration board, the other side must be connected to a signal source such as the Audio Precision analog outputs or a DVD player

2.2 Output configuration

The TDA7498E demonstration board has been configured in 2-channel BTL output.

2.3 Connections

The board terminals (top view of demonstration board) are visible in Figure 2.

Figure 2. TDA7498E demonstration board connections

Left Load Right Load

Gain selection

Single-ended input/differential input mode selection

Doc ID 022507 Rev 1 5/22

Analog input

Standby and mute

controls

Schematic diagram and PCB layout AN4015

3 Schematic diagram and PCB layout

Figure 3. TDA7498E schematic

6/22 Doc ID 022507 Rev 1

AN4015 Schematic diagram and PCB layout

Figure 4. PCB layout - top side

Figure 5. PCB layout - bottom side

Doc ID 022507 Rev 1 7/22

+ 15 hidden pages