• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 2 answers
  • Subscribers 14 subscribers
  • Views 2251 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.

Receive upto 20MHz digital differential signals using ISO3086T

Bailin Cao
Expert 1120 points
Other Parts Discussed in Thread: ISO3086T, ISO1176T, ISO7821LL, ISO1176

Hello there,

I would like to use ISO3086T to receive digital differential signals from a twisted pair. From its data sheets, on page 4, max (1/ tUI) = 20 Mbps. However, I can't find the definition of tUI anywhere else in the datasheets. Please clarify this.

Many thanks1

  • 0
    TI__Intellectual 2900 points

    Hi Bailin,

    Max data rate will be = 1/tUI (20Mbps for ISO3086T). tUI stands for time duration of Unit Interval.

    Please do refer to below App Note for additional clarity on RS485 parameters.
    www.ti.com/.../slla070d.pdf

    Regards,
    Anand Reghunathan

  • 0 in reply to Anand Reghunathan
    Expert 1120 points

    Hi Anand,

    Thanks for your reply.

    In term of clock speed, ISO3086T can operate at the max clock speed of 10MHz which is equivalent to 20 Mbps. To transfer signals of 20 MHz, ISO1176T should be used instead although some pins are left unconnected and wasted. Can you suggest a better solution. Thanks.

    Kind regards,

    Bailin

  • 0 in reply to Bailin Cao
    TI__Intellectual 2900 points
    Hi Bailin,

    I hadn't seen the 20MHz requirement. Apologies for the miss. You are correct ISO1176T should be used instead.

    Alternatively you can use ISO7821LL for receiving digital differential signals and use a discrete transformer driver like SN6505 for generating isolated power. This alternate solution can give you reduced emissions and reduced power consumption as compared to ISO1176T.

    Regards,
    Anand Reghunathan
  • 0 in reply to Anand Reghunathan
    Expert 1120 points
    Hi Anand,

    Thank you for your reply.

    Comparing ISO1176T with ISO7821LL, I found the following differences from their data sheets.

    1. ISO1176T is galvanic isolation while ISO7821LL has capacitor isolation. In term of noise rejection, ISO1176T is better.
    2. The transmitter and receiver of ISO7821LL are all differential. More I/O pins are required to interface with it although it can go at higher speed.
    3. More parts are required to generate an isolated power for ISO7821LL such as SN6505 and an extra clock source.

    After the above considerations, what do think?

    Kind regards,

    Bailin
  • 0 in reply to Anand Reghunathan
    Expert 1120 points
    Hi Anand,

    If a few of ISO1176Ts share a VCC2 power supply generated by a LDO and a transformer driven by D1 and D2 of one of ISO1176T, can D1 and D2 pins of the rest ISO1176Ts be left open?

    Many thanks,

    Bailin
  • 0 in reply to Bailin Cao
    TI__Guru 55795 points
    Hi Bailin,

    Yes, D1 and D2 pins of any ISO1176T can be left open as the push-pull converter in ISO1176T is an open-loop system and doesn't anticipate any feedback. Alternatively one other option is to use one of ISO1176T to generate VCC2 and the rest of RS-485 devices can be ISO1176 (device without push-pull converter). Please note that both of these devices have different pin-out.

    Regards,
    Koteshwar Rao
  • 0 in reply to Koteshwar Rao
    Expert 1120 points
    Hi Koteshwar,

    From the data sheets of ISO1176T, the absolute maximum rating of the transformer driver output current, ID1 or ID2 is 450 mA. Is it the peak current at 350KHz or the max continuous current? What is its recommended peak current at 350KHz? If the peak current of ID1 or ID2 at 350KHz is 300mA, for example, do this mean that it can provide 300mA DC on average on the primary side of the transformer used in the typical application shown on page 1 in the data sheets?

    Many thanks and kind regards,

    Bailin
  • 0 in reply to Bailin Cao
    TI__Intellectual 2900 points

    Hi Bailin,

    As you may already know. D1 and D2 switch ON and OFF as below. Both are never ON at the same time.

    The absolute maximum of 450mA shows the maximum amount of current that can flow through either D1 or D2 when respective drive pin is ON.

    If peak current is 350mA at 350kHz, then 350mA can flow through D1 when D1 is ON and similarly it can flow through D2 when D2 is ON. The IC will be able to drive a continuous load of 350mA.

    Hope this answers your query.

    Regards,
    Anand Reghunathan