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Powering the ADM2565E

Category: Datasheet/Specs
Product Number: ADM2565E
I am using the ADM2565E - RS485 HALF DUPLEX transceiver.
In the datasheet there is a VCC voltage that will support either 3.3V or 5.0V input. 
I am connecting the RxD and TxD pins to an FPGA that is working on 3.3V levels.
The RS-485 signals coming into the transceiver will be at 5.0V levels.
The question is... Should my VCC input voltage be 3.3V or 5.0V?
By setting VIO to 3.3V will that give me the 3.3V levels interface on the RxD and TxD pins?
THEN, by setting Vsel = Viso, will the RS-485 external connections will be at 5.0V?
Will Viso be 5.0V even if I set VCC = 3.3V?
Any clarification on this would be appreciated.
Thank you,
  • Hi Mike,


    Sorry for the late response.


    For ease of reading I report here the datasheet of the ADM2565E:

    ADM2561E/ADM2563E/ADM2565E/ADM2567E (Rev. B) (


    As you rightly noted, this device has a VIO logic flexible I/O supply separated from VCC to allow communication with interfaces at different voltages. In particular, the VIO supply accepts a supply voltage between 1.7 V and 5.5 V, allowing communication with 1.8 V, 2.5 V, 3.3 V, and 5 V devices. In your case, as anticipated by you, I suggest to connect VIO (pin 7) to 3.3V to have this voltage level on RxD and TxD, matching the voltages of the FPGA.

    For further information you can consult the paragraph "1.7 V TO 5.5 V VIO LOGIC SUPPLY" on page 23 of the datasheet.


    Talking about the isolated power supply, when Vsel = Visoout, the Viso set point is 5.0 V. Considering that your bus works at that level, I suggest to use this setting. You can find the Vsel pin function description in table 12 of the datasheet (page 12).


    Finally, assuming that Viso = 5V for your application, it is recommended that VCC is connected to 5V.


    Table 14 of the datasheet (page 20), shown also below for simplicity, summarizes the possible configurations of the isolated DC-DC Converter with the associated voltage range needs.



    I hope I have been helpful and clarified your doubts. If you have any other questions do not hesitate to contact us.


    Good work,