AN-550 Datasheet, PDF (1/11 Pages) Holt Integrated Circuits – This application note provides recommendations

August 2008
AN-550
Hardware Design Considerations
For MIL-STD-1553 Terminals
Introduction
This application note provides recommendations for
hardware design for bus interface circuitry within MIL-
STD-1553 terminals. This document describes interface of
terminal logic to the transceiver, transceiver connection to
the bus isolation transformer, and transformer
interconnect to the MIL-STD-1553 bus. Methods are
described to achieve proper terminal operation that
complies with the MIL-STD-1553B standard.
Comprised of both digital and analog circuitry, terminal
design includes several important factors to consider
related to device selection and placement, circuit routing,
grounding, and the use of decoupling capacitors. In
addition, designers should be mindful of several physical
factors affecting MIL-STD-1553 terminal performance;
these factors are discussed.
Figure 1 shows typical terminal interconnect to a MIL-STD-
1553 bus. The standard defines two types of bus coupling.
Direct-coupled terminals are connected to the bus by a
stub cable not more than 1 foot (30cm) long. Although the
application should use the shortest cable that meets
physical interconnect needs, transformer-coupled
terminals may use a stub cable up to 20 ft (6m) long. Most
VDD
GND
VDD
Transmit
Receive
VSS
MIL-STD-1553
Protocol Logic
VDD
TX
BUS
TX
RCV
RCV ^BUS
VSS
Bus
Transceiver
MIL-STD-1553
Terminal Boundary
Isolation
Transformer
CT
*CT
55 Ohm
Isolation
Resistors
* This center tap is
often not connected
Termination
Resistor
R = Z_O
L
Shielded
Twisted Pair
Stub Cable
L = 1 ft (30 cm) max.
VDD
GND
Direct-Coupled MIL-STD-1553 Terminal
VDD
Transmit
Receive
VSS
MIL-STD-1553
Protocol Logic
VDD
TX
BUS
TX
RCV
RCV ^BUS
VSS
Bus
Transceiver
MIL-STD-1553
Terminal Boundary
Isolation
Transformer
CT
*CT
* This center tap
is often not
connected
Transformer-Coupled MIL-STD-1553 Terminal
Shielded Twisted Pair
MIL-STD-1553 Data Bus
( Z_O = 70 to 85 Ohms,
commonly 78 Ohms)
Bus Coupler
L
Coupling
Transformer
Isolation
Resistors
R = 0.75 Z_O
N = 1:1.41
Shielded
Twisted Pair
Stub Cable
L = 20 ft (6 m) max.
Termination
Resistor
R = Z_O
Figure 1. TRANSFORMER-COUPLED AND DIRECT-COUPLED TERMINALS
HOLT INTEGRATED CIRCUITS
(AN-550 Rev. NEW)
www.holtic.com
8/08