• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 32 subscribers
  • Views 827 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

RS422 differential minimal output voltage

Patrick MARCOT
Prodigy 30 points
Other Parts Discussed in Thread: DS34C87T

Hello,

We're using a DS34C87T driver in our product and one of our customer ask if he can use it with a consecutive electronic which requires a differential voltage min of 2.5V.

Regarding the spec of the product below, the minimal differential voltage for the driver is 2.0V with the specified supply of 5V +/-10% = 4.5 to 5.5V.

Question: if customer monitor the voltage supply and guarantee that this will not drop under 5.0V, can we certify that output differential voltage would be 2.0 + 0.5V = 2.5V ?

Or what parameter could help to increase this voltage ? Driver load would be approx 100 Ohm.

Thanks for help.

 

  • 0
    TI__Expert 3175 points

    Hi Patrick,

    On DS34C87T datasheet, it specifies these 2 parameters

    VOL = 2.5V min

    VOH = 0.5 V max

    These parameters are valid for supply VCC = 5V+-5%

    With these specifications, over the supply voltagae range of 5V +-5%, the single-ended swing VOL to VOH is 2.5-0.5 = 2.0V min

    The differerntial swing, ie the P-signal minus the N-signal is 4.0Vp-p min

    In your note, I saw you mentioned "required a differential voltage min of 2.5V", I need your confirmation if you mean single-end output, or differential output.

    Regards,

    TK Chin

  • 0 in reply to T.K. Chin
    Prodigy 30 points

    Hi TK Chin,

    Thanks for reply.

    It's a differential line : load of approx 100 Ohm between inverting and non-inverting outputs.

    I don't find where you have found the 4.0vpp min ?

    In the datasheet, for me it corresponds to the VT spec with the RL load (differential between inverting and non-inverting outputs) which specifies 2.0Vmin

    Thanks for your opinion.

    Best regards,

    Patrick

  • 0 in reply to Patrick MARCOT
    Prodigy 30 points
    Hello,
    Could someone help me on my request ?
    Thanks,
    Patrick
  • 0 in reply to Patrick MARCOT
    TI__Expert 3175 points
    Hi Patrick,
    The datasheet has 3 parameters: VOL, VOH, and VT.

    VOL of each P- or N- signal is max 0.5V,
    VOH of each P- or N- signal is min 2.5V
    So the P-signal minus the N-signal is a signal that swing between +2.0V and -2.0V, and thus 4Vpp.
    VT parameter is min 2.0V, which is peak voltage from 0V, or half the peak-to-peak differential voltage.
    I will check with my colleague to double check the above too.

    regards,
    TK Chin