AN10327

AN10327 TDA856x and TDA8571J power amplifiers Rev. 01.00 — 15 October 2004 Application note Document information Info Keywords Abstract Content Automotive, audio, power amplifier, Stereo, Quad, BTL, class AB, bipolar This document contains application information for the power amplifier TDA856x series and the TDA8571J Philips Semiconductors AN10327 TDA856x ,TDA8571J Revision history Rev 1.0 Date 20041015 Description First version Contact information For additional information, please visit: http://www.semiconductors.philips.com For sales office addresses, please send an email to: sales.addresses@www.semiconductors.philips.com © Koninklijke Philips Electronics N.V. 2004. All rights reserved. Application note Rev. 01.00 — 15 October 2004 2 of 19 Philips Semiconductors AN10327 TDA856x ,TDA8571J 1. Introduction 1.1 Amplifier overview This document describes the application specific subjects of the following audio power amplifiers : TDA856x family and TDA8571J. These amplifiers, which are made in a bipolar process, are mainly used in automotive applications such as car radios, boosters and multimedia applications. The differences between the types are mainly the number of output channels, different load values and output power. The following matrix shows an overview of the mentioned amplifiers and their properties. Table 1: Amplifier Overview * DDD = Dynamic Distortion Detection Channels Gain [dB] TDA8560Q TDA8562Q TDA8563Q TDA8563AQ TDA8566Q TDA8566TH TDA8567Q TDA8568Q TDA8569Q TDA8571J 2 x BTL 4 x SE 2 x BTL 2 x BTL 2 x BTL 2 x BTL 4 x BTL 4 x BTL 4 x BTL 4 x BTL 40 20 20 20 26 26 26 40 26 34 Load [Ohm] 2 4 2 2 2 2 4 4 2 4 2 x SE 4 x SE 2 x SE 2 x SE 2 x diff. 2 x diff. 4 x SE 4 x SE 4 X SE 4 x SE Inputs Output power [W] 2 X 40 4 x 12 2 x 40 2 x 40 2 x 40 2 x 40 4 x 25 4 x 25 4 x 40 4 x 26 DDD* [%] 10 10 10 2.2 7.5 10 10 10 10 10 DBS13P DBS17P DBS13P DBS13P DBS17P HSOP20 DBS23P DBS23P DBS23P DBS23P Package © Koninklijke Philips Electronics N.V. 2004. All rights reserved. Application note Rev. 01.00 — 15 October 2004 3 of 19 Philips Semiconductors AN10327 TDA856x ,TDA8571J 2. Application Information 2.1 Input capacitors The amplifiers need capacitors on the inputs to get a DC decoupling of the input source (pre-amplifier stage). The impedance of the input stage together with the input capacitors, create a low frequency roll-off point. A larger input capacitor means a lower frequency roll-off point. The values that should be used are mentioned in the datasheet of the amplifier type. The following figure shows the influence of the input capacitors on the frequency roll-off point for the TDA8566TH. (A) Input capacitor 470nF (B) Input capacitor 220nF (C) Input capacitor 100nF Fig 1. Roll-off frequency at different input capacitor values The low frequency roll-off point can easily be calculated : 1 2 ⋅ π ⋅ Z in ⋅ Cin _ tot © Koninklijke Philips Electronics N.V. 2004. All rights reserved. f low _ −3dB = Application note Rev. 01.00 — 15 October 2004 4 of 19 Philips Semiconductors AN10327 TDA856x ,TDA8571J For example the low frequency roll-off point for the TDA8566TH, when using 220nF input capacitors, equals : 1 2 ⋅ π ⋅ 120 ⋅ 10 3 ⋅ 110 ⋅ 10 −9 f low _ −3dB = = 12 Hz In this case the total input capacitance is halved since the input source is “seeing” the input capacitors in series. This is due to the differential input configuration which is drawn in the next figure. Fig 2. Differential input stage TDA8566TH Furthermore it is recommended to use input capacitors with a low DC leakage (film capacitors), since any DC leakage at the inputs will result in a DC offset at the outputs. Electrolytic capacitors usually have a relatively high DC leakage and should therefore not be used. 2.2 Differential inputs The TDA8566 is provided with differential input circuits. This has the advantage that disturbances on the inputs, with relation to ground, are greatly eliminated. However, if there’s a mismatch of the input capacitors, the common mode rejection ratio (CMRR) decreases for low frequencies, since the impedance of the input capacitors will increase then. © Koninklijke Philips Electronics N.V. 2004. All rights reserved. Application note Rev. 01.00 — 15 October 2004 5 of 19 Philips Semiconductors AN10327 TDA856x ,TDA8571J The next figure shows the CMRR of the different input capacitor configurations : (A) 100nF input capacitors, unmatched (