SLLA556 June 2021 ISOS141-SEP , SN65C1168E-SEP
Parameter | Design Requirement |
---|---|
Bit rate | 100kbps to 10Mbps |
Bus length | 12M to 1500M |
Maximum Total Ionizing Dose | 30krad(Si) |
Maximum SEL to LET | 43MeV × cm2/mg |
Isolation voltage | 3000VRMS per UL1577 |
In spacecraft applications RS-422 might be used as a bus and payload telecommand and control interfaces. RS-422 was designed as serial communication methods to convey information between equipment by using balanced and differential twisted-pair cable. RS-422 is specified for multi-drop applications where only one driver connects up to 10 receivers through a single differential twisted bus. The following figure shows a typical half-duplex isolated RS-422 interface circuit.
The following circuit uses the ISOS141-SEP digital isolator and SN65C1168E-SEP transceiver devices to achieve a space-grade isolated RS-422 driver.
The previous circuit uses the SN65C1168E-SEP driver to create an isolated RS-422 driver to isolate the primary device from the secondary devices. SN65C1168E-SEP consists of two receivers and can be used as secondary devices.
RS-422 system can transmit up to 10Mbps, or over a 1500-m cable at a lower signaling rate. The signal rate is reciprocal to the cable length. Hence, it is important to figure out the maximum signal rate for a given cable length or vice versa. The following figure shows the RS-422 recommended signal rate over the cable length in its annex.
This system design uses a 1500-m cable. From the previous figure, the maximum recommended signal rate is 90kbps.
Parameter | Conditions | Typ (ns) | MAX (ns) |
---|---|---|---|
Propagation delay of ISOS-141-SEP | With RL = 50Ω, CL = 15pF | 10.7 | 16 |
Propagation delay of TX to bus | With RL = 50Ω, CL = 40pF | 8 | 16 |
Propagation delay of 1500-m wire | Approximate delay is 5ns/m (Typ), 5.3ns/m (Max) | 7500 | 7950 |
Propagation delay of bus to RX | With RL = 50Ω, CL = 50pF | 15 | 27 |
Note: If the path delay is greater than the bit time, the following options apply:
ISOS141-SEP | |
---|---|
VCC1, VCC2 | 2.25 V to 5.5 V |
Data-rate | 10Mbps |
Propagation delay | 10.7ns to 16ns |
TID Characterized (ELDRS-Free) | 30krad(Si) |
TID RLAT, RHA | 30krad(Si) |
CMTI | ±100kV/µs |
VISO | 3000 VRMS |
http://www.ti.com/product/ISOS141-SEP |
SN65C1168E-SEP | |
---|---|
VCC1 | 4.5 V to 5.5 V |
Data-rate | 1MHz |
TID Characterized (ELDRS-Free) | 30krad(Si) |
TID RLAT, RHA | 20krad(Si) |
Common Mode Range | –7 V to 7 V |
http://www.ti.com/product/SN65C1168E-SEP |
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