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Data Device Corporation
www.ddc-web.com
BU-64703
D-03/06-0
+3.3V INTERFACE TO MIL-STD-1553 BUS
The SSRT Mark3 is the world's first MIL-STD-1553 terminal
powered entirely by 3.3 volts. Unique isolation transformer turns
ratios, single output winding transformers and new interconnec-
tion methods are required in order to meet mandated MIL-STD-
1553 differential voltage levels.
FIGURE 15 illustrates the two possible interface methods
between the SSRT Mark3 series and a MIL-STD-1553 bus.
Connections for both direct (short stub, 1:3.75) and transformer
(long stub, 1:2.7) coupling, as well as nominal peak-to-peak volt-
age levels at various points (when transmitting), are indicated in
the diagram.
The new isolation transformers for the SSRT Mark3 series now
contain only one set of output windings. Different isolation trans-
formers are now required for a direct or transformer coupled,
MIL-STD-1553 Bus implementation.
The center tap of the primary winding (the side of the trans-
former that connects to the SSRT Mark3) must be directly con-
nected to the +3.3 volt plane. Additionally a 10f, low inductance
tantalum capacitor and a 0.01f ceramic capacitor must be
mounted as close as possible and with the shortest leads to the
center tap of the transformer(s) and the ground plane.
SSRT Mark3
BU-64703X8/9
DATA
BUS
Z
0
55
55
(1:3.75)
(7.4 Vpp)
28 Vpp
1 FT MAX
Z
0
(1:2.7)
20 Vpp
(1:1.41)
COUPLING
TRANSFORMER
0.75 Z
0
0.75 Z
0
LONG STUB
(TRANSFORMER
COUPLED)
20 FT MAX
28 Vpp
SHORT STUB
(DIRECT COUPLED)
OR
DIRECT-COUPLED
ISOLATION TRANSFORMER
BETA LVB-4103
NOTES:
1. Transformer center tap capacitors: use a 10F tantalum for low inductance, and a 0.01F ceramic.
Both must be mounted as close as possible, and with the shortest leads to the center tap of the
transformer(s) and ground.
2. Connect the SSRT Mark3 hybrid grounds as directly as possible to the 3.3V ground plane.
3. Z0 = 70 to 85 Ohms.
SSRT Mark3
BU-64703X8/9
(7.4 Vpp)
TRANSFORMER-COUPLED
ISOLATION TRANSFORMER
BETA LVB-4203
7 Vpp
10F
.01F
+
3.3V
10F
.01F
+
3.3V
TX/RX
FIGURE 15. SSRT Mark3 +3.3V INTERFACE TO MIL-STD-1553 BUS