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TPS546C23EVM1-746: External synchronization

Thomas Mandal Nilsen
Prodigy 20 points
Part Number: TPS546C23EVM1-746
Other Parts Discussed in Thread: TPS546C23

Tool/software:

I want to synchronize the Master of the evaluation board to an external clock. As a start I tried to pull the SYNC pin to BP3 (through 10k) to make sure it would run freerunning until the sync becomes available. But then I realized it didn't start at all. Then I tried to pull the SYNC to BP6, but the result is still the same. What is the expected behavior here? Is it not possible to power up the device in freerunning mode and switch to external synchronization when the extarnal clock becomes available?

  • 0
    TI__Guru 56825 points

     

    Thomas Mandal Nilsen said:
    What is the expected behavior here?

    This is the expected behavior in the default programmed configuration.  The TPS546C23 is not intended to operate in 2-phase mode without a SYNC signal to the follower device, as that causes the two converters to operate at different frequencies, which will create a beat-frequency equal to the difference in the free-running frequencies of the two converters.  

    Thomas Mandal Nilsen said:
    Is it not possible to power up the device in freerunning mode and switch to external synchronization when the extarnal clock becomes available?

    Through PMBus programming, the two-phase configuration can be forced to ignore a SYNC FAULT.  The MISC_CONFIG_OPTIONS command (Command Code F0h) https://www.ti.com/lit/ds/symlink/tps546c23.pdf#page=76 has an option to disable the SYNC_FAULT (High byte, Bit 0) this will allow the follower device to enable without a SYNC from the external SYNC or from the primary of the stack.

    The OPTIONS command (command code E5h) https://www.ti.com/lit/ds/symlink/tps546c23.pdf#page=73 also has an option to force SYNC_IN so that the SYNC pin does not need to be externally pulled up.