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TPS50601A-SP: SYNC Pin Tied Together Across Multiple Devices in Internal Oscillator Mode

Jim Y
Prodigy 120 points
Part Number: TPS50601A-SP


Are there any issues with tying the SYNC pins all together among multiple devices, even if they’re all operating in internal oscillator mode with their own unique RT resistor connected between the RT pin and GND, configured for different switching frequencies and different output voltages?

  • 0
    TI__Genius 14540 points

    The SYNC pins should not be tied together if each converter is operating at a unique switching frequency determined by its RT resistor.  SYNC pin is intended to synchronize converters operating at the same switching frequency.  What you are describing is phase locking all the converters operating at different frequencies while using the internal oscillators.  I am not aware of a way to achieve this and am curious why such operation is needed.

    Thanks

    Christian

  • 0 in reply to Christian Yots
    Prodigy 120 points

    Hi Christian,

    Thank you for your response.  I'm looking to have the flexibility to switch between master/slave mode and internal oscillator mode with multiple devices.  It would be nice if I could simply just keep the SYNC pins tied together for master/slave mode (i.e. depopulating the RT resistor of the selected master device and switch at the default 500kHz) or change over to internal oscillator mode (i.e. populate a RT resistor for all the devices) and simply not use the SYNC feature (i.e. populate a 10kΩ across the SYNC node to ground).

    Hope that makes sense.

    Regards, - James

  • 0 in reply to Jim Y
    TI__Genius 14540 points

    HI James,

    Ok that makes more sense.  I thought you were wanting to dynamically switch between architectures without BOM changes.  In theory, this should work as the SYNC pin will not be an output clock if the RT resistor is populated on every converter.  When switching over to master/slave mode, the RT on the master is removed and the RT on all other converters must be changed to set  500kHz switching.  Keep in mind, we recommend a 1kohm to ground termination on the SYNC pin to mitigate against single event upsets.  Having said that, I guess the only risk now of tying all SYNC pins together is that, should a radiation induced transient happen on one converter's SYNC pin, it could propagate to all other converters, causing them to temporarily switch to external sync mode.  Since you must change BOM between architectures why not isolate each SYNC with a 0-ohm resistor so that each converter has its own 1kohm to ground closeby.

    Thanks

    Christian

  • 0 in reply to Christian Yots
    Prodigy 120 points

    Thanks for the detailed response, Christian.  

    Our design does use 0-ohm resistors to provide the option of isolating each converter when operating the devices in internal oscillator mode and we'll keep it this way in order to mitigate against radiation induced upsets per your recommendation.

    I've appreciated the help! - Jim