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SN6505B-Q1: Push pull and MCU on same rail

Antoine Chapuis1
Expert 3575 points
Part Number: SN6505B-Q1
Other Parts Discussed in Thread: TCAN11623-Q1, TCAN11625-Q1, SN6505B

Hi team,

In an ECU supplied with a CAN SBC like TCAN11623-Q1, is it possible to have the SBC supply SN6505B-Q1 with 3.3V, and an MCU on the same rail?

The alternative is TCAN11625-Q1, with 5V to the SN6505B-Q1, and an LDO to do 3.3V for MCU, but that is an extra LDO.

Do you have some insights there ? The pushpull output is unregulated 8-16V, 15mA current

Best regards,

Antoine

  • 0
    TI__Genius 17100 points

    Hi Antoine,

    Thank you for posting to E2E! SN650x devices can be connected on shared input power supply rails, and the recommended operating range for SN6505 supports either 3.3V or 5V in, so both options are possible.

    So long as the input power supply can provide sufficient current to power the isolated 15mA load, the SN6505, transformer, and MCU, there should not be be any problems. Please ensure a decoupling capacitor of 0.1uF - 1uF is connected to and placed closely to the SN6505 Vcc pin and a decoupling capacitor of about 10uF is connected to and placed closely to the primary-side center tap pin of the isolation transformer.

    Please let us know if there is any additional information we can provide.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Expert 3575 points

    Hi Manuel,

    Thanks, I would be very interested in seeing efficiency curves of a SN650x 5V-5V, at low output current ratings, lets say in the 30 or 50mA range: do you have such figures? I would also be interested to see these figures for 3.3V to 5V conversion, same output current of 30-50mA.

    Isolation rating is 2500Vrms min. I think the Wuerth transformers are more than OK for this exercise.

    This will be helpful to convince the customer that there is headroom for the CAN SBC to supply both pushpull stage and MCU.

    Best regards, Antoine

  • 0 in reply to Antoine Chapuis1
    TI__Genius 17100 points

    Hi Antoine,

    Thank you for following up.

    Efficiency curves of SN6505 devices with 3.3V to 3.3V, 5V to 5V, and 3.3V to 5V transformers are included in the Typical Characteristics section of their datasheets. Below are a few examples:

    5V to 5V


    3.3V to 5V:


    Since we do not have data for every commercially available transformer, if our customer would like to evaluate additional or specific transformer part numbers, we recommend they order either an SN6501, SN6505B, or SN6505A EVM and replace the transformer.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Expert 3575 points

    Manuel,

    Thank, this is the exact data I was looking for! I cannot find these datasheets: I am using this page, but I keep getting the transformer footprint and high level specs like DC resistance and inductance,.. not detailed application curves.

    Can you please direct me to these datasheets?

    Best regards, Antoine

  • +1 in reply to Antoine Chapuis1
    TI__Genius 17100 points

    Hi Antoine,

    I'm glad this is what you're looking for! Not all transformer datasheets include output efficiency and voltage vs. load current curves, like this Bourns datasheet or this PCA datasheet do.

    Images shown above were captured from the SN6505B datasheet found here (PDF) and here (html).


    Please let me know if there is more information we can help with Slight smile


    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Expert 3575 points

    Hi Manuel,

    Many thanks, that was all I needed

    Best regards, Antoine