LTC3862-1 RS485 Network Biasing

Hi All,

As per LTC3862-1 datasheet (under "RS485 Network Biasing" section): 

"The LTC2862-LTC2865 transceivers will operate correctly on biased, unbiased, or under-biased networks".

Does this mean if we use LTC2862-1 in applications which has external network biasing resistors for fail safe, will this be ok? Do we see any problem in using LTC2862-1 in multi drop applications which has RS485 network biasing resistors also in the RS485 daisy chain?



  • +1
    •  Analog Employees 
    on May 4, 2021 12:26 PM

    Hi Pradeep, 

    That's correct, the receiver of the LTC2862-1 will work correctly if the network has external failsafe biasing resistors.

    The failsafe feature of the LTC2862-1 means that the receiver will also have failsafe functionality on a network without failsafe biasing resistors. 



  • 0
    •  Analog Employees 
    on May 4, 2021 12:27 PM

    Hi Pradeep,

    It just says there's no need for external biasing IF all the transceivers have similar internal failsafe features. You don't need external fail safe resistors  "in that case only" as they normally add to the bus load. Normally, the value of the biasing resistors depends on the number and type of transceivers on the line and the number and value of terminating resistors. So if you get rid of one the transceiver for example, you'll need to change the biasing resistors value due to under biased/over biased network this will create. Therefore, the values of the biasing resistors must be customized to each specific network installation, and may change if nodes are added to or removed from the network. With the internal failsafe, you don't need to care about the external biasing applied. That's all. And yes, if the rest of the transceivers on your network don't have internal fail safe, you may use an external biasing network for them. LTC2862 should operate normally regardless of the biasing condition of the network.