• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 34 subscribers
  • Views 417 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

SN65HVD888: SN65HVD888 DIFFERENTIAL TERMINATION

Rajan
Intellectual 270 points
Part Number: SN65HVD888

HI,

As per SN65HVD888DR datasheet Application Information mentioned RL DIFFERENTIAL TERMINATION for 54 Ω.

For 120Ω.RL DIFFERENTIAL TERMINATION suggest suitable RFS PULLUP / RFS PULLDOWN resistor value.

Thanks 

Rajan

  • 0
    TI__Mastermind 25705 points

    Rajan,

    The 54Ohm termination takes all load into account. For example, assume you have two 120Ohm termination at both ends of communication. With some nodes attached to the bus (RX input resistance), the equivalent resistance becomes 54Ohm.

    If you want to have a fail-safe bias on the bus, you can refer to this app note for the details. The basic idea is to create a 120Ohm with the termination and 2 RSF, while the bus voltage is biased around 200mV to 250mV in idle.

    Please let me know if you have more questions.

    Regards,

    Hao

  • 0 in reply to Hao L
    Intellectual 270 points

    Hi Hao,

    Thank you for your support.

    Please let me know SN65HVD888 chip R,RE,DE and D pins source and sink maximum current rating for finalize pull up/down resistor value.

    Chip VCC= 5V

    Thanks

    Rajan  

  • 0 in reply to Rajan
    TI__Mastermind 25705 points
    Rajan,

    R is an output pin, which can sink/source up to 8mA current. Internally D and REB have pull down resistors, while DE has pull down. The value is about 1MOhm. Please let me know if you have more question.

    Regards,
    Hao
  • 0 in reply to Hao L
    Intellectual 270 points

    Hi Hao,

    Thank you for your support,

    As per SN65HVD888 datasheet Electrical Characteristics VOH Receiver high-level output voltage MIN = 2.4V and TYP = VCC – 0.3 for IOH = –8 mA. 

    I can't able to see the different IOH current with respect to VOH graph image.

    So please let us know for 2 and 4mA IOH current respective VOH MIN value.

    Thanks 

    Rajan 

  • 0 in reply to Rajan
    TI__Guru 62920 points
    Hi Rajan,

    Hao is out of the office, so I will try to help. The VOH minimum value is specified at the maximum output current since this is a worst-case condition. (Higher output current leads to a lower output voltage due to the voltage loss across the non-zero output resistance of the driver circuit.) So, at lower IOH levels, the VOH level will become increasingly close to VCC. (We unfortunately do not have the specific values at each current that you mentioned.)

    Regards,
    Max