ST AN585 Application note handbook
Contents
1. AN585 ky APPLICATION NOTE ISDN INTERFACE PROTECTION INTRODUCTION The choice of a suitable protection device for an ISDN line interface requires consideration of a parameter which is not critical in analogue line applications the parasitic capacitance that the device introduces Be cause of the high data rates used parasitic capacitances must be minimized in order to ensure correct signal transmission In particular attention must be paid to the capacitance imbalance in the line which can cause considerable signal degradation Such imbalance most frequently results from the presence of common mode protection in which the capacitance introduced between each line and earth is frequently unequal STMicroelectronics has developed a complete range of specific protection devices for ISDN applications the TRIBALANCED PROTECTION TPIxx series These devices introduce only a minimum of capacitance imbalance 30pF which does not affect the transmission performance of the line TRIBALANCED PROTECTION TPIXX SERIES The use of TRIBALANCED protection is mandatory under the following conditions The bias voltage on line A and line B is different line A GND Line B Vbat The protection is realized in common mode as illustrated in Figure 1 b In this case two conditions must be satisfied 1 Low capacitance from line to ground gt No signal attenuation 2 Good capacitance balance between line a and line b Good longitudinal bal2. ance on the line Figure 1 ISDN interface protection o o o U INTERFACE U INTERFACE OR AH TPIxx OR S INTERFACE S INTERFACE o o o a FLOATING GROUND b ABSOLUTE GROUND REFERENCE REV D2A 3597 April 2004 1 5 AN585 APPLICATION NOTE ISDN PROTECTION PRODUCT RANGE STMicroelectronics offers specific protection devices for ISDN interface protection The product range is given in Table 1 which shows that this function is available with different package versions Discrete and monolithic versions are available in order to provide a wide choice of cost performance com promises Depending on the solution chosen different recommendations apply with regard to the optimum configu ration to use Figure 2 illustrates the typical application schematic for TRIBALANCED PROTECTION When the discrete solution is used three components per line are necessary Table 1 Tribalanced protection product range DISCRETE SOLUTION MONOLITHIC DEVICES 3 devices per line SOD15 CB429 S08 DIL8 HIGH SURGE CAPABILITY MEDIUM SURGE CAPABILITY 75A 10 1000 msec 30A 10 1000 msec SMTHDT58 TPU58 TP18011P TPI8012P SMTHDT80 TPU80 TP112011P TP112012P SMTHDT120 TPU120 Figure 2 Tribalanced protection functional schematic DISCRETE MONOLITHIC SOLUTION SOLUTION 3 x SMTHDTXX 3 x TPUxx TPIxx o o o o o o A
3. gt i g a AF AF Y LOW CAPACITANCE LINE GND gt NO SIGNAL ATTENUATION GOOD CAPACITANCE BALANCE A LINE B GOOD LONGITUDINAL BALANCE ON THE LINE APPLICATION SCHEMATICS Figure 3 and 4 illustrate the use of tribalanced protection in a u interface and an s interface respectively In each case there is the choice of a discrete solution SMTHDTxx or TPUxx where a high surge capability is required or a single chip solution for low cost TPIxx Thus cost a nd performance can be traded ina variety of combinations All of these components are innovative and ideal for use in high speed transmis sion lines 2 5 ky AN585 APPLICATION NOTE Figure 3 Central office PABX U Interface protection TPUxx Zs TPIxx V w 5 DI SMTHDTxx LINE U I PTC ABSOLUTE GND REFERENCE Figure 4 NT1 S Interface protection U INTERFACE S INTERFACE BAT42 gt i 1 TPixx i D SMTHDTxx BATA2 i TPU iy l x Lact it Ei E TE 56 mn 3 E e 5 d l TPIxx i ours oo SMPs oe CONCLUSION Due to the sensitivity of ISDN to capacitance imbalance on the lines tribalanced protection has to be used where common mode protection of lines wi
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5. th different bias voltages is required ST offers a wide range of devices designed specifically for ISDN protection enabling this requirement to be satisfied ky 35 AN585 APPLICATION NOTE REVISION HISTORY Table 2 Revision History Date Revision Description of Changes March 1993 1 16 Apr 2004 2 First Issue Stylesheet update No content change 4 5 4 AN585 APPLICATION NOTE Information furnished is believed to be accurate and reliable However STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics Specifications mentioned in this publication are subject to change without notice This publication supersedes and replaces all information previously supplied STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics The ST logo is a registered trademark of STMicroelectronics All other names are the property of their respective owners 2004 STMicroelectronics All rights reserved STMicroelectronics GROUP OF COMPANIES Australia Belgium Brazil Canada China Czech Republic Finland France Germany Hong Kong India Israel Italy Ja
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ST AN585 Application note handbook