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AN153
Compatibility Between CS4299 and AD1881
INTRODUCTION
This application note will discuss the problems and possible solutions that are associated with populating a CS4299 into a socket designed for the AD1881. Although the AC '97 spec recommends a standard pinout for all AC '97 compliant codecs, there are subtle differences in the value and hookup of external components that can cause non-interoperability between AC '97 codecs from different manufacturers. The following concerns are of particular interest for customers considering using a CS4299 instead of an AD1881. Vrefout on a CS4299 will drain the internal reference and prevent the reference from charging to its nominal level. Consequently, the REF bit in register 26h will not be set which in turn will signal an error condition to the controller. Any external loading on Vrefout must be buffered on the CS4299. There's no easy workaround for designs that load Vrefout.
3. AFLT Capacitors
The AFLT caps are spec'ed at 270 pF/NPO for the AD1881 and at 1000 pF/NPO for the CS4299. Running the CS4299 with the 270 pF/NPO caps on AFLT will result in somewhat higher distortion and lower dynamic range on the ADC's, but probably still be acceptable. These caps are easily interchangable since the larger cap is available in the same footprint as the smaller one and a replacement is recommended. If a surface mount ceramic cap (any manufacturer, size code 0805) was used originally, replace with KEMET(R) C0805C102J5GAC.
1. Reference Capacitors
AD1881 requires 10 F + 0.1 F caps on pin 27 (called Vref) while the CS4299 requires 1 F + 0.1 F caps on pin 27 (called REFFLT). If a CS4299 is populated into an AD1881 socket, the Crystal part's reference would charge ten times slower than intended and the part might fail calibration or finish calibration with considerable offsets remaining in the analog path and converters. Depending on layout it may be possible to exchange the 10 F cap for a 1 F cap with similar footprint. In particular, if the original design uses a 10 F surface mount tantalum cap (Panasonic(R) TE series, size code Y) it is easily replaced with a 1206 surface mount ceramic cap (PHILIPS(R) 12062F105M8BB0 or KEMET C1206C105M8VAC).
4. 3D Capacitors
To complete the 3D circuitry, the AD1881 requires a 100 nF cap between pins 33 (called CX3D) and 34 (called RX3D). In addition, the AD1881 requires a 47 nF cap between pin 34 and AGND. Furthermore, the AD1881 requires 1 F/ELEC caps from pins 32 (called FILT_L) and 31 (called FILT_R) to AGND. The CS4299 on the other hand requires a 1000 pF cap between pins 33 (called FLTI) and 34 (called FLTO), as well as a 0.01 F cap from pin 32 (called FLT3D) to AGND. Because of the vastly different cap values and connectivity, dropping a CS4299 into an AD1881 socket will almost certainly render the 3D feature on the
2. Vrefout Buffering
The AD1881 is designed to source up to 5 mA from Vrefout. Some systems use this feature to supply the microphone bias directly from Vrefout. The CS4299 on the other hand can only source about 100 nA from Vrefout. This is sufficient to bias external op-amps, but running the mic bias off of
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Copyright (c) Cirrus Logic, Inc. 1999 (All Rights Reserved)
JUN `99 AN153REV1 1
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CS4299 useless. It should however be possible to change an existing socket to accept a CS4299 by: * replacing the 100 nF cap between pins 33 and 34 with a 1000 pF cap, if a surface mount ceramic cap (any manufacturer, size code 0805) was used originally, replace with KEMET C0805C102J5GAC removing the 47 nF cap between pin 34 and AGND, replacing the 1 F cap between pin 32 and AGND with a 0.01 F cap, if a surface mount tantalum cap (Panasonic TE series, size code Y) was used originally, replace with KEMET C1206C103K5RAC removing the 1 F cap between pin 31 and AGND.
5. Output Filtering Capacitors
Finally, the AD1881 doesn't require external filter caps on the analog outputs. The CS4299 spec's 680 pF to 1000 pF caps from all used analog outputs to AGND. Since the corresponding pads do not exist on an AD1881 socket it will be hard to add these caps after the fact. The CS4299 will still function properly without these caps, but out of band energy from the DAC modulators will increase on the analog outputs. This could cause distortion on the amplifiers of the following stage if they cannot slew fast enough to keep up with the high frequency components in the analog output. This may or may not be acceptable and requires tests on the part of the vendor.
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ADDENDUM
A schematic as well as gerber drawings have been included that show how to accommodate both devices in a single layout. They may be used as a guideline for designs that wish to be compatible with both, the CS4299 and the AD1881.
Contacting Cirrus Logic Support
For a complete listing of Direct Sales, Distributor, and Sales Representative contacts, visit the Cirrus Logic web site at: http://www.cirrus.com/corporate/contacts/
PANASONIC is a registered trademark of Matsushita Electric Industrial Company, Ltd. PHILIPS is a registered trademark of Philips Electronics KEMET is a registered trademark KEMET Electronics Corporation Preliminary product information describes products which are in production, but for which full characterization data is not yet available. Advance product information describes products which are in development and subject to development changes. Cirrus Logic, Inc. has made best efforts to ensure that the information contained in this document is accurate and reliable. However, the information is subject to change without notice and is provided "AS IS" without warranty of any kind (express or implied). No responsibility is assumed by Cirrus Logic, Inc. for the use of this information, nor for infringements of patents or other rights of third parties. This document is the property of Cirrus Logic, Inc. and implies no license under patents, copyrights, trademarks, or trade secrets. No part of this publication may be copied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photographic, or otherwise) without the prior written consent of Cirrus Logic, Inc. Items from any Cirrus Logic website or disk may be printed for use by the user. However, no part of the printout or electronic files may be copied, reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photographic, or otherwise) without the prior written consent of Cirrus Logic, Inc.Furthermore, no part of this publication may be used as a basis for manufacture or sale of any items without the prior written consent of Cirrus Logic, Inc. The names of products of Cirrus Logic, Inc. or other vendors and suppliers appearing in this document may be trademarks or service marks of their respective owners which may be registered in some jurisdictions. A list of Cirrus Logic, Inc. trademarks and service marks can be found at http://www.cirrus.com.
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U1 +5VA +3.3VD DVdd1 DVdd2 1 9 DVdd1 DVdd2 DVss1 DVss2 R1 R2 47 BIT_CLK SDATA_OUT SDATA_IN SYNC RESET# LINE_OUT_L LINE_OUT_R ALT_LINE_OUT_L ALT_LINE_OUT_R MONO_OUT S/PDIF_OUT EAPD ID0# ID1# 45 46 FILT_R nc1 nc5 nc6 nc7 31 40 43 44 48 47 37 39 41 35 36 LINE_OUT_L LINE_OUT_R ALT_LINE_OUT_L ALT_LINE_OUT_R MONO_OU T CHAIN_CLK EAPD +3.3VD 6 5 8 10 11 DGND 47 4 7 AGND ABITCLK ASDOUT ASDIN ASYNC ARST# LINE_OUT_L LINE_OUT_R AVdd1 AVdd2 25 38 AVdd1 AVdd2 AVss1 AVss2 26 42
RX3D
FILT_L
ALT_LINE _OUT_L
ALT_LINE_OUT_R
LINE_OUT_L
LINE_OUT_R
MO NO_OUT
C11 680pF NPO DGND
C12 680pF NPO
C13 680pF NPO
C14 680pF NPO
C15 680pF NPO
DGND
+ C16 1uF ELEC
FILT_R
+ C17 1uF ELEC
+ C19 C18 0.047uF 10uF X7R ELEC
AD1881 only
AGND
CS4299 only
AGND
for CS4299 use values as shown for AD1881 * replace C5/6 with 270pF/NPO * replace C8 with 100nF/X7R
+VA
+VD
DVdd1
AVdd1
4
+ C20 10uF ELEC C22 0.1uF Z5U pin pin 7 C24 0.1uF Z5U C25 0.1uF Z5U
C21 0.1uF Z5U
AVdd2
+ C23 10uF ELEC
pin 26
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AGND
pin 42
DGND
DVdd2
Vref
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CS4299
AD1881: Vrefout sources 5 mA current C S4299: Vrefout must be buffered
CS4299 only
Vrefout
PC_BEEP PHONE AUX_L AUX_R VIDEO_L VIDEO_R CD_L CD_GND CD_R MIC1 MIC2 LINE_IN_L LINE_IN_R PC_BEEP PHONE AUX_L AUX_R VIDEO_L VIDEO_R CD_L CD_GND CD_R MIC1 MIC2 LINE_IN_L LINE_IN_R
12 13 14 15 16 17 18 19 20 21 22 23 24
ALT_LINE_OUT_L ALT_LINE_OUT_R MONO_OU T S/PDIF_OUT
CS4299 only
EAPD
28 27 29 30 32 33 34 Vrefout REFFLT AFLT1 AFLT2 FLT3D FLTI FLTO XTL_IN XTL_OUT 2 3
AD1881 only
C1 1uF Y5V
C2 0.1uF X7R
C3 1uF Y5V
C4 0.1uF X7R
C5 1000pF NPO
C6 1000pF NPO
C7 0.01uF X7R
Vrefout Vref AFLT1 AFLT2 FILT_L RX3D CX3D C8 1000pF NPO
Y1 AGND C9 24.576 MHz 22pF NPO C10 22pF NPO
Figure 1. Schematics
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Figure 2. Assembly
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Figure 3. Top Layer
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Figure 4. Bottom Layer
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* Notes *

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