• Resolved

THVD1450: GPD of 1.4V

Intellectual 2885 points

Replies: 3

Views: 20

Part Number: THVD1450

Hello,

I have an application for the THVD1450 where the signal to power ground differential is 1.4V. Would operating this device at 5V (which would create aVoc of 2.5V) be acceptable? Are there any other parameters we need to consider because of this 1.4V GPD?

Thanks,

Nick

  • Hi Nick,

    Would this GPD be between the THVD1450's GND and the grounds references of other RS-485 nodes sharing the same network (via A, B pins)?  If so, this is no problem - RS-485 transceivers must support a minimum common mode range of -7 V to +12 V (per EIA-485 physical layer standard requirements) in order to be robust against ground shifts between nodes.

    Or, would this GPD be between the THVD1450's logic interface pins (D, R, DE, /RE) and the rest of the system?  In that case, you would want to check whether there is enough margin between VOH/VIH and VOL/VIL specifications for the proper logic states to always be detected.

    Regards,
    Max

  • In reply to Max Robertson:

    I believe his would apply to the former on the A/B pins. To maybe explain further:

    1. Voltage on "A/B" output during low state and GND plane at distance 0 (right at the pins) are the same, so the differential is 0V
    2. Voltage on "A/B" output during low state and GND at distance "X" (lets say 10m, for example) are different, up to a 1.4V differential

    Best,

    Nick

  • In reply to Nicholas Carley:

    Hi Nick,

    This is OK for RS-485 interfaces.  They are generally not so sensitive to the absolute voltages but rather to the differential between them (i.e., VA - VB).  As long as the GPD is not so great that the specified common mode range of the transceivers is exceeded, communication should work fine.

    Max