SLLA635 May   2024 THVD4411 , THVD4421 , THVD4431

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 Application Use-Case of Multiprotocol Transceivers
  6. 3 Key Design Goals of a Versatile Multiprotocol Transceiver
  7. 4 Discrete Multiprotocol Transceiver Implementation
  8. 5 TI's THVD44xx Multiprotocol Transceiver Family
  9. 6 MODE Configurations for THVD4431
  10. 7 Application Diagrams for THVD4431
  11. 8 Waveforms for THVD4431
  12. 9 Benefits of THVD4431 Over Competition Devices
  13. 10Conclusion

4 Discrete Multiprotocol Transceiver Implementation

With the above design goals in mind, discrete multiprotocol implementation can be realized as shown in Figure 4-1.

Discrete Multiprotocol Solution Implementation Figure 4-1 Discrete Multiprotocol Solution Implementation

The OptoMOS that connects driver and receiver non-inverting terminals together (Q3) and inverting terminals together (Q4) are used to make the solution switch between half and full duplex. Q1 and Q2 OptoMOS are used to switch ON or OFF the 120Ω termination resistor to make the node either a terminal node or a middle node. The solution can look functionally OK, but there is one issue that degrades the performance of the RS-485 system. Integrated RS-232 devices in the market have 5kΩ resistor on RS-232 receiver pins to ground which are still present even if the solution is configured as RS-485. This loads the RS-485 receiver and reduces the number of nodes supported by RS-485. Clearly, a discrete solution is tricky to design, requires considerable external components and occupies a lot of board space, making the overall solution expensive and bulky.