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SN65HVD75: about the RS-485 receiver output current

Vera Mao
Expert 5065 points
Part Number: SN65HVD75

dear supporting team,

do we have higher than 8mA receiver  output current RS-485 transceiver?  

the background is :  customer has 5 loads in the bus which is very far away from the 485 transceiver.  customer originally used SN65HVD11D,  found it is not enough, and they change to SN65HVD75.  it seems has better result.

while from d/s, in recommend operating condition,  sn65hvd75 and SN65HVD11D has same limitation of 8mA, while from absolute rating,  sn65hvd75 is 24mA versus 11mA of  SN65HVD11D, does this means  sn65hvd75 has higher driver ability than SN65HVD11D? 

tks!

  • 0
    TI__Guru 62920 points
    Hi Vera,

    Unfortunately, all of our 3.3-V/half-duplex RS-485 transceivers have their receiver output voltage levels specified based on a standard load current of 8 mA. Higher absolute maximum ratings do often correspond to stronger drivers (i.e., ones with lower output resistance), but this is not always the case.

    On the current board, are there any pull-up or pull-down resistors populated on the receiver output? If so, what is the resistance value? Is there an issue with the output high level being too low, or is the low level too high? Are you able to observe the waveforms on a scope to verify that the receiver output voltage levels are the root cause of the problem?

    Best regards,
    Max