SLLA628 September   2023 THVD1424

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Use Case Domain of RS-485
    1. 1.1 RS-485 Compliant Transmitter
    2. 1.2 RS-485 Compliant Receiver
    3. 1.3 RS-485 Transceiver Use Case Variability
  5. 2Traditional RS-485 Design Process
    1. 2.1 Design Process Overview
    2. 2.2 Requirement Definition
      1. 2.2.1 Bus Voltage and Logic Voltage (VCC and VIO):
      2. 2.2.2 Number of Communication Nodes Supported plus Static vs. Dynamic Systems
      3. 2.2.3 Max Bus Length, Network Topology, Emission Concerns, and Data Rate Required
      4. 2.2.4 Duplex
      5. 2.2.5 Protection Needs
      6. 2.2.6 Additional Features of RS-485 Bus
    3. 2.3 IC Selection, Application Design, and Validation/Qualification
  6. 3One Multi-System Design: Flexible RS-485 with the THVD1424
    1. 3.1 Flexible Multi-System Design
    2. 3.2 Simplification of RS-485 Design Process Using THVD1424
      1. 3.2.1 Bus Voltage and Logic Voltage Supplies (VCC and VIO)
      2. 3.2.2 Number of Communication Nodes Supported plus Dynamic or Static Systems
      3. 3.2.3 Max Bus Length, Network Topology, Data Rate, and Emissions Concerns
      4. 3.2.4 Duplex
      5. 3.2.5 Protection Needs
      6. 3.2.6 Additional Features
  7. 4Summary
  8. 5References

Number of Communication Nodes Supported plus Dynamic or Static Systems

The THVD1424 is a 1/8 unit load device which allows up to 256 1/8 unit load devices on one differential bus. This is typically the max bound for RS-485 systems so this device can be fit into any RS-485 bus up to 256 nodes. With the THVD1424 also has a benefit in dynamic systems with its integrated termination resistors. Using the HVAC example from section 2.2 – imagine that the 50-node bus is going to be increased to 51 nodes where the new additional node becomes an end node. In traditional RS-485 systems node 49 (unterminated) has a different design than node 50 (terminated) so that means that node 51 needs to conform to node 50’s design while node 50 must be reconfigured to be like node 49. This increases the chances of a technician in the field making a mistake causing a communication failure which could lead to system downtown while the problem is identified. The THVD1424 solves this problem by allowing termination to be controlled by an input on a logic pin – allowing for a simple way to change nodes between unterminated and terminated; which also cuts down on the issue of needing multiple node designs.