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Integrated Mixed-Signal Solutions
STAC9766 and STAC9750 Motherboard Implementation for AC'97 Codecs with Integrated Headphone Amplifiers
SigmaTel Application Note
Version 1.0
2-AN011-1.0-0701
Copyright (c) 2001 SigmaTel, Inc. All rights reserved. All contents of this document are protected by copyright law and may not be reproduced without the express written consent of SigmaTel, Inc. SigmaTel, the SigmaTel logo, and combinations thereof are trademarks of SigmaTel, Inc. Other product names used in this publication are for identification purposes only and may be trademarks or registered trademarks of their respective companies. The contents of this document are provided in connection with SigmaTel, Inc. products. SigmaTel, Inc. has made best efforts to ensure that the information contained herein is accurate and reliable. However, SigmaTel, Inc. makes no warranties, express or implied, as to the accuracy or completeness of the contents of this publication and is providing this publication "AS IS". SigmaTel, Inc. reserves the right to make changes to specifications and product descriptions at any time without notice, and to discontinue or make changes to its products at any time without notice. SigmaTel, Inc. does not assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential, or incidential damages.
STAC9766 and STAC9750 Motherboard Implementation for AC'97 Codecs with Integrated Headphone Amplifiers
The AC'97 audio codec specification provides for a standard LINE_OUT 1Vrms analog output, as well as an optional output on pins 39 and 41, that may be either a headphone amplifier output, or a True Line Output. Earlier codecs did not support the headphone amplifier driver capability, and the main LINE_OUT output was usually routed to the output connector through a simple AC-coupling circuit. Several codecs have been released to the market that support an internal headphone drive amplifier, including the STAC9766 and the STAC9750 audio codecs. To best take advantage of the new codecs with headphone support as well as the older designs with very high quality output amplifiers driving the LINE_OUT pins, the configuration in the figure below is suggested. Both outputs are routed to the primary output connector through the ac-coupling capacitors, but only one set of accoupling capacitors is installed. For traditional codecs that do not support the internal headphone amplifier, the standard LINE_OUT outputs should be connected with the primary set of ac-coupling capacitors. For Modern codecs that provide an internal headphone driver the secondary output should be connected to the output connector as indicated in the AC'97 specification through the alternate set of accoupling capacitors. For proper adherence to the WHQL testing requirements for frequency response, headphone amplifier ac-coupling capacitors should be 220uF for 32-ohm headphone drive, while the typical LINE_OUT output can be connected with 3.3uF capacitors to drive 2k ohm and larger loads. The optional EMI suppression circuit is recommended, but not required.
Standard LINE_OUT Configuration Primary ac-coupling Capacitors Alternate ac-coupling Capacitors C1 and C2 Installed Do Not Install Capacitor Installation Table Internal Headphone Amplifier Configuration Do not Install C3 and C4 Installed
Alternate AC - Coupling Capacitors ***
C3 +220uF/6.3V
C4 +220uF/6.3V
HP R 41
HP L 39
+
(Headphone)
+
EMI Suppression Circuit (Optional)
C5 1000pF C1 +3.3uF/16V Line_Out R Line_Out L 36 35 +
R1 47K
L1 HZ0805E601R-00 2 3 4 5 1
LINE OUT
AC'97 Audio Codec
C2 +3.3uF/16V
+
Primary AC - Coupling Capacitors ***
C6 1000pF
R2 47K
L2 HZ0805E601R-00
J1
CUI SJ-3535N
*** Note: 220uF ac-coupling capacitors will drive loads of 32 ohms and greater and still meet the bandwidth requirements of PC2001. 3.3uF ac-coupling capacitors will drive loads of 10K ohms and greater and still meet the bandwidth requirements of PC2001.
The STAC9766/67datasheet, product brief and additional information is available at www.sigmatel.com.
2
2-AN011-1.0-0701

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