RCD16-47B

October 1998 - Ed : 2A

NETWORK OF 16R-C-D LINETERMINATIONS
RESISTANCE : R = 47

, TOLERANCE +/- 10%

CAPACITANCE: C = 33 pF, TOLERANCE +/- 10%
SCHOTTKY DIODE : (D)

FEATURES

In any electronic equipment where a suitable bus
termination is requiredto avoid signal reflectionsand
distortions :

PC and workstation computer
Data-line analyzers

MAIN APPLICATIONS

FUNCTIONAL DIAGRAM

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.

RCD NETWORK

FOR BUS TERMINATION

Application Specific Discretes

A.S.D.

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.

BENEFITS

MIL STD 883C - Method 3015-6

- V

= 2 kV

C= 100 pF

R = 1500

- 3 positive strikes and 3 negativestrikes (F= 1Hz)

COMPLIESWITH THE FOLLOWING STANDARDS:

SO20

SSOP20

R = 47

tolerance

+/- 10 %

C = 33 pF, tolerance +/- 10 %

D = Schottky diode

1/7

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.

APPLICATION NOTE : BUS TERMINATION

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 produced by 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.

RCD16-47B

2/7

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 ASD

technology(*).

The ASD

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.

(*) ASD

= Apllicaion Specific Discretes.

RCD16-47B

3/7

Symbol

Parameter and test conditions

Typ.

Max.

Unit

Connection resistance (note1)

amb

= 25

0.25

Total capacitance

F = 1 MHz, V

= 0V, V

RMS

= 30 mV

Leakage current

= V

RRM

= 25

= 70

Forward voltage

= 1 mA

= 16 mA

= 25

0.5

Note 1 : Rc is the resistance between pin 1 and pin 11 or between pin 10 and pin 20

ELECTRICAL CHARACTERISTICS

Symbol

Parameter

Value

Unit

Total power dissipation per package

500

Continuous forward current per Schottky diode

RRM

Repetitive peak reverse voltage

7.5

Maximum electrostatic discharge
MIL STD 883C - METHOD 3015-6

stg

Storage temperature range
Maximum junction temperature

- 55 to + 150

150

ABSOLUTE MAXIMUM RATINGS (0

amb

Symbol

Parameter

Package

Value

Unit

th(j-a)

Junction to ambient

SO20

SSOP20

100
140

C/W

THERMAL RESISTANCE

RCD16-47B

4/7

Part Number RCD16-47B