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(R)
RCD16-47B
RCD NETWORK FOR BUS TERMINATION
Application Specific Discretes A.S.D.TM
MAIN APPLICATIONS In any electronic equipment where a suitable bus termination is requiredto avoid signal reflectionsand distortions : PC and workstation computer Data-line analyzers DESCRIPTION With the increasing speed of data transmission, line reflections provide signal distorsions and the overshoots or undershootsproduced on the signal edges can cause the malfunction of the whole system. To avoid these negative effects from leading to problems, a suitable termination is required. Dedicated to bus termination, the RCD16-47B provides by far the best method to minimise stray emissions from PCB tracks. FEATURES NETWORK OF 16R-C-D LINETERMINATIONS RESISTANCE : R = 47 , TOLERANCE +/- 10% CAPACITANCE: C = 33 pF, TOLERANCE +/- 10% SCHOTTKY DIODE : (D) BENEFITS Provides impedance matching, thus increasing noise immunity and minimizing distortion. Lowers EMI / RFI radiation. No DC power dissipation. Eliminates negative voltages : no current will change the bias of the protected device. Uses the best of all termination schemes.
SO20
SSOP20 FUNCTIONAL DIAGRAM
1 2
20 19
3 4 5 6
18 17
16 15
7 8
14 13
9 10
12
11
COMPLIESWITH THE FOLLOWING STANDARDS: MIL STD 883C - Method 3015-6 C= 100 pF R = 1500 - VPP = 2 kV - 3 positive strikes and 3 negativestrikes (F= 1Hz)
October 1998 - Ed : 2A
R = 47 , tolerance +/- 10 % C = 33 pF, tolerance +/- 10 % D = Schottky diode
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RCD16-47B
APPLICATION NOTE : BUS TERMINATION With the increasing speed of data transmission (PC, TV, ...), engineersare naturally confrontedwith effects that were of less significance with slower circuits. Among these are the effects described in transmission line theory : line reflections provide signal distortions and the overshoots or undershoots produced on the signal edges can finally cause the malfunction of the whole system.
1. Reflection at a non terminated line The figure below shows the circuit of a transmission system in which a memory device (input impedance of 100 k) is connected at the end of a line with line impedance Zo.
10
100 k
If this line is not properly terminated, a certain amount of the energy is reflected back, inducing a reflection phenomena that can distort the signal. This can result in improper operation of the system. The simulation shown on the above figure illustrates the signal distortion producedby line reflection at the end of the line which is not well terminated. Even if the signal at the start of the line has the correct form (upper curve), considerable distortion arises at the end of the line (lower curve). On the positive edge, the overshoot can exceed the maximum operating voltage of the used circuit technology which will then be destroyed. Also, the following negativeundershoot may reach a level low enough to change the value of the logic state. If it affects of an address line, a wrong memory cell will be addressed, and in the case of a data line, the data can be corrupted. This phenomena also occurs on the falling edge.
To avoid these negative effects from leading to problems in a system, a suitable termination is required.
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RCD16-47B
2. The RCD termination The traditional solution to properly match each line of the bus consists of the use of several discrete resistances, capacitors and small schottky diodes. For a 16-bit bus, this requires 48 discrete components. SGS-THOMSON offers an innovating solution with a monolithic structure using ASDTM technology(*). The ASDTM technologyenables to integrate monolithically 16 of these RCD "basic cells" onto a single chip device. The RCD16-47B reduces component cost and assembly cost, saves board space and improves reliability.
The simulation illustrates the signal distortion produced by line reflection at the end of the line when such a termination is used. The resistor provides the path termination for PCB track, thus resulting in low reflection phenomena. The capacitor of 33 pF blocks DC currents while acting as a short circuit during signal transitions, and holds the bus at the last logic level. It reduces power consumption and avoids excessive current. The small Schottky diode clamps the negative remaining undershoots which can result from impedance mismatch. This damps negative voltages and prevents the logic signal from rising above the logic level '0' threshold after a falling edge.
The RCD termination provides optimal solution compared to all other termination techniques.
(*) ASDTM = Apllicaion Specific Discretes.
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RCD16-47B
ABSOLUTE MAXIMUM RATINGS (0C Tamb 70C) Symbol P IF VRRM VPP Tstg Tj Parameter Total power dissipation per package Continuous forward current per Schottky diode Repetitive peak reverse voltage Maximum electrostatic discharge MIL STD 883C - METHOD 3015-6 Storage temperature range Maximum junction temperature Value 500 50 7.5 2 - 55 to + 150 150 Unit mW mA V kV C C
THERMAL RESISTANCE Symbol Rth(j-a) Parameter Junction to ambient Package SO20 SSOP20 Value 100 140 Unit C/W
ELECTRICAL CHARACTERISTICS Symbol RC Ct IR VF Parameter and test conditions Connection resistance (note1) Total capacitance Leakage current Forward voltage Tamb = 25C 45 1 10 0.5 1 Typ. Max. 0.25 Unit pF A V
F = 1 MHz, VR = 0V, VRMS = 30 mV VR = VRRM IF = 1 mA IF = 16 mA Tj = 25 C Tj = 70 C Tj = 25 C Tj = 25 C
Note 1 : Rc is the resistance between pin 1 and pin 11 or between pin 10 and pin 20
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RCD16-47B
PSPICE MODEL per RCD CELL
L 3 nH SO20 1.75 nH SSOP20 R1 3 R3 9
R2 47
Cvar C1 33pF Cvar
Dschot
Dschot parameters
Cvar parameters
t
SO20 Package Z magnitude versus frequency
Phase versus frequency
SSOP 20 Package Z magnitude versus frequency
Phase versus frequency
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RCD16-47B
ORDER CODE
RCD
Product 16 cells
16
-
47
B
RL
Packaging: : tube RL : tape & reel package : B = SO20 B6 = SSOP20
R = 47
Product RCD16-47B RCD16-47B6
Package Tube SO20 SSOP20 40 66
Base Qty Tape & reel 1000 2000
MARKING Type RCD16-47B RCD1647B6 Package SO20 SSOP20 Marking RCD1647B RCD1647B6
Packging : Preferred packaging is tape and reel.
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RCD16-47B
PACKAGE MECHANICAL DATA SO20 (Plastic)
DIMENSIONS REF.
D hx45 A B e A1
K L
Millimeters Inches Min. Typ. Max. Min. Typ. Max. 2.35 0.10 0.33 0.23 12.6 7.40 1.27 10.0 0.25 0.50 10.65 0.394 0.75 0.010 1.27 0.020 8 (max) 2.65 0.20 0.51 0.32 13.0 7.60 0.092 0.004 0.013 0.009 0.484 0.291 0.050 0.419 0.029 0.050 0.104 0.008 0.020 0.013 0.512 0.299
C
E
H
A A1 B C D E e H h L K
SSOP20 (Plastic) DIMENSIONS
L
REF. A A1 A2 b c D E E1 e k L
Millimeters Inches Min. Typ. Max. Min. Typ. Max. 2.00 0.25 2.00 0.35 0.35 8.05 8.70 6.22 0.079 0.010 0.059 0.079 0.010 0.012 0.014 0.004 0.014 0.278 0.317 0.299 0.343 0.198 0.240 0.245 0.026 10 0 10 0.80 0.010 0.020 0.031
A2 A
b D e k E
A1
c
20
11
E1
1 10
1.51 0.25 0.10 7.05 7.60 5.02 0 0.25
0.30
6.10 0.65 0.50
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 infringementof 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 (c) 1998 STMicroelectronics - Printed in Italy - All rights reserved. STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Mexico - Morocco The Netherlands - Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A. http://www.st.com 7/7

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