SLLA628 September 2023 THVD1424
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.