• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 32 subscribers
  • Views 1271 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.

SN65LVDM176: Isolation for half-duplex LVDS?

Aaron L
Prodigy 110 points
Part Number: SN65LVDM176
Other Parts Discussed in Thread: ISO7821LL, ISO7710, SN6501

I inherited a design using SN65LVDM176 half-duplex LVDS transceiver. Speeds in application are fairly pedestrian (up to 25mbps). The LVDS pair is sent between 2 separate boards, each possibly using different power supplies. Only the LVDS data lines might be common between the boards. The transceivers can be damaged on a hotplug (and/or pull) event as well as if one board is not connected to a power supply (not grounded) but receiving some signal on LVDS lines from a powered board. I'm investigating solutions to this issue and thinking that isolating the transceiver from the incoming LVDS signaling to prevent current from entering the transceiver until a ground and power has been established might be a solution to the issues observed.

I understand that hotplug/pull could possibly be alleviated by forcing ground to be connected first in a mechanical solution, but the connector type being used doesn't have this feature and may be out of the question for this design. This also wouldn't solve the issue with one board ungrounded but receiving LVDS signals.

  1. Is isolation a solution to the problems described?
  2. I haven't seen any specific isolated half-duplex LVDS transceiver reference designs. Are there any examples available?
  3. Recommendation on isolation part that could be paired with SN65LVDM176DR or one of the newer M-LVDS compliant transceivers?

Any assistance and advice would be greatly appreciated.

  • 0
    TI__Genius 10250 points
    Hello Aaron,

    I will look into this and get back to you.

    Regards,
    Yaser
  • 0 in reply to Yaser Ibrahim
    TI__Genius 10250 points

    Hi Aaron,

    Sorry for the delay in responding.  I was checking with the isolation products team (probably should've reassigned this thread to them!).  

    There is a solution to achieve isolation for half duplex LVDS.  It requires more than one device though as shown below.

    Regards,

    Yaser

    SN6501 drives a transformer for an isolated power supply for side 2 of the ISO7821LL and ISO7710. ISO7821LL can be used for half duplex LVDS. ISO7710 controls the enable of the ISO7821LL. This should improve noise immunity of your system.

    For hot plug, we could consider some TVS diodes on the bus to protect the ISO7821LL.

    For more of an integration play, the SN6501 +Transformer + LDO + ISO7710 can be replaced by ISOW7821 (integrated data and power isolation product). The ISOW can also power the ISO7821LL.