ADUM3402 and ADM3078 versus ADM2682

I have an existing RS485 half duplex design using the ADUM3402, the ADM3078 running at 3.3V and a DC-DC convertor. I'm looking to save some space (as always) and am considering using the ADM2682. However, I've been trying to interpret the supply current specifications, and however I look at it, the single device solution apprears to require about twice the current under the same conditions (60R load). There doesn't appear to be a spec. for the power conversion efficiency, so am I misinterpreting the specs? I need a low-power solution.

On the subject of the ADM3078, are there any known issues with the fail-safe detection features? I appear to get false start characters from the receiver on a low-capacitance bus (<600pF approx, 2 x 120R terminators) when the the transmitter turns off, with a baud rate of 240k. Once the bus capacitance rises above about 600pF, the voltage collapse appears to be slow enough for this not to happen.

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    •  Analog Employees 
    on Oct 24, 2013 9:40 AM

    Hi NTipping,

    What DC-DC convertor are you using? Is it an isoPower solution, such as the ADuM5000?

    The power conversion efficiency is not specified for the ADM2682E, it is restricted by the small size of the internal transformer and this is the reason for the high supply current.

    In order to achieve maximum integration (lowest board space), but a lower power solution than the ADM2682E, i can suggest using the ADM2485. The ADM2485 has integrated an RS-485 transceiver, iCoupler signal isolation, and a transformer driver into a single package. The ADM2485 will operate at lower power than the ADM2682E.

    Please see the ADM2485 datasheet pp16 Figure 34, which shows an applications diagram.

    For your second question can you please provide some more information?

    Are you refering to a Transmitter and Receiver on the same ADM3078 transceiver? Or on seperate bus nodes?

    Is there a Pull-Up resistor on the RO?

    Regards,

    Richard Anslow

Reply
  • 0
    •  Analog Employees 
    on Oct 24, 2013 9:40 AM

    Hi NTipping,

    What DC-DC convertor are you using? Is it an isoPower solution, such as the ADuM5000?

    The power conversion efficiency is not specified for the ADM2682E, it is restricted by the small size of the internal transformer and this is the reason for the high supply current.

    In order to achieve maximum integration (lowest board space), but a lower power solution than the ADM2682E, i can suggest using the ADM2485. The ADM2485 has integrated an RS-485 transceiver, iCoupler signal isolation, and a transformer driver into a single package. The ADM2485 will operate at lower power than the ADM2682E.

    Please see the ADM2485 datasheet pp16 Figure 34, which shows an applications diagram.

    For your second question can you please provide some more information?

    Are you refering to a Transmitter and Receiver on the same ADM3078 transceiver? Or on seperate bus nodes?

    Is there a Pull-Up resistor on the RO?

    Regards,

    Richard Anslow

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