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SN65HVD1792-EP common-mode range of -20 to +25V.

David Fishman
Prodigy 30 points

Can I take the common-mode range specification to mean that the device will fully function without performance or reliability degradation if the the device is used on 2 boards with power supplies that are +25V apart?

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    TI__Expert 5400 points

    David,

    Not quite.  The grounds of the respective boards should be within +20V and -20V of each other.  For if one device were 25V above a second device, then the second device would be 25V below the first, which is a clear violation of the spec.

    So why is the spec unbalanced?  Consider two boards, A and B, where GNDB = GNDA + 20V.  During operation, the bus pins on board A will see levels from GNDB to VCC(B), or from +20V to +25V.  Conversely, the bus pins on board B will see levels from GNDA to VCC(A), or -20V to -15V.  So any given device must be able to operate from -20V to +25V, even though the maximum ground potential difference is limited to -20V to + 20V.

    This is the same reason the RS-485 spec is -7V to +12V.