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Original question:

THVD1500: D pin need a pullup resistor?

THVD1500: Do Pull up and Pull down resistors necessary for A and B pins?

Manu Chang
Intellectual 2040 points
Part Number: THVD1500
Other Parts Discussed in Thread: THVD1505, SN65HVD888

Tool/software:

Hi,

My customers before are using 485 transceiver from competitors and are used to add 10kohm pull up resistor on A pin and 10kohm pull down resistors on B pins. Currently they turned to THVD1500 and found that 10kohm pull down and pull up is too big and might cause some signal distortion. They decrease the value to 2kohm and then it looked good. However, they still have concerns/questions about this pull up/down resistors:

1. Are these pull up/down resistors on A & B pins necessary? especially for the long range communication via 485 and have around 20 nodes of whole bus (customers use case).

2. if customers would like to add these resistors, do we have recommend values for these resistors?

BR,

Manu

  • 0
    TI__Genius 13872 points

    Hello Manu,

     

    The pull-up/pull-down resistors are not necessary for the THVD1500. This device already has it integrated internally. 

      

    For your attached image, the SN65HVD888 devices have auto polarity detection which requires the pull-up/pull-down resistors (failsafe-biasing). If you are looking for this feature, the THVD1505 incorporates auto polarity detection. In this case, the failsafe resistor configuration in the image below is required:

    Best,

    Ethan