MA28139 Datasheet, PDF (22/34 Pages) Dynex Semiconductor – OBDH Bus Terminal

MA28139
CONNECTIONS TO THE OBDH I, R AND BT BUSSES (SUGGESTED SCHEMES ONLY)
TRANSMITTER
XR4
XR2
XR3n
XR1n
XR4
XR2
XR3n
XR1n
Two OBDH bus driver schemes based on complementary and N-channel enhancement-mode FETs are shown.
Current-limiting and protection resistors may be employed to prevent damage under short-circuit.
Latching and/or non-latching relays may be used to provide isolation from the bus when a redundant circuit is unused or unpowered.
NPN and/or PNP bipolar junction transistors may also be employed in place of FETs.
Redundancy can be handled in channels (as shown) or by applying cross-strapping between the transformers and the drivers.
This implementation generates ‘active ground’ pulses where the transformer is shorted out (by conduction of the two lower FETs)
while the bus driver is enabled to reduce ringing, bus echoes, etc.
Using XR2 in place of XR3n and XR4 in place of XR1n will not cause ‘active zeros’ to be driven.
Figure 19: Conceptual OBDH Bus Driver Scheme
22/34