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Synchronizing multiple controllers and SYNC signal galvanic isolation

Denis Kotlar
Intellectual 790 points
Other Parts Discussed in Thread: LM5574, LM5118, ISO7421

I'd like to synchronize two PSU modules which will be housed in the same box. They have to be galvanically isolated. Each PSU module will have two controller: LM5118 and LM5574. I'd like to synchronize all of them from single controller (one that has the highest frequency achieved by Rt value). Since communication between controllers has to be bidirectional I'd like to use isolator such as ISO7221 or ISO7421 to "disconnect" one PSU module from the other connected as shown on the picture below. Please let me know if the proposed solution is ok.

  • 0
    Intellectual 790 points

    After some additional thinking I came to conclusion that using transformer instead of isolator is a better approach. So, the main question remain same: Synchronizing 4 controllers with galvanic isolation between two pairs.
    I found two possible solution: one is Murata pulse transformer and some of Coilcraft's coupled inductor (1:1 ratio) that is normally used for SEPIC or similar topology.

  • 0 in reply to Denis Kotlar
    Intellectual 790 points

    A small update if someone else wondering about synchronization of different controllers such as proposed LM5574 and LM5118. I've succeed to do that with LM5574 as a master (runs on higher frequency) and LM5118 as a slave. It works fine under various Vout and load conditions. Here a couple of screenshots with LM5118 working in buck and buck-boost mode:

    (HO and LO are LM5118 outputs, SW is LM5574 output).

  • 0 in reply to Denis Kotlar
    Intellectual 790 points

    I finally had a chance to test sync signal isolation. Here is a schematic with synchronized LM5574 (master) and LM5088-2 on one PCB and LM5574 on another isolated PCB.

    The following screenshot presents a case when PCBs are not in sync:

    And below you can see how they look synchronized: