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TPS50601-SP: Synchronization Timeout

Part Number: TPS50601-SP

I'm unclear about how the external synchronization mode works.   This is the description in the datasheet:


In external synchronization mode, a resistor is connected between the RT pin and GND. The Sync pin requires a

toggling signal for this mode to be effective. The switching frequency of the device goes 1:1 with that of Sync pin.

External system clock-user supplied sync clock signal determines the switching frequency. If no external clock

signal is detected for 20 μs, then TPS50601-SP transitions to its internal clock, which is typically 500 kHz.



I bolded the text at issue.  Does this imply that I need to start the external clock within 20 us?  Or is it possible to let the regulator start in the default (500 kHz), then begin external synchronization seconds or minutes later?   I feel like being able to start synchronizing later is typical for switching regulators, but the datasheet seems to imply that it might not be ok?





  • Hi Patrick,

    An excellent question.

    I tend to agree with you that starting synchronization later should be fine.

    1) If the RT pin is populated then RT pin determines the converter frequency. Now when an external clock is there via Sync pin, then frequency set by the sync pin overrides the frequency set by RT pin. External clock frequency should be within 5% of frequency set by RT pin.
    RT pin is also required for proper slope compensation.

    However in order to ensure that there are no unknown glitches, timing issues , I would have to test it and confirm so no abnormalities are experienced. Thus will provide you further update on it.
  • In reply to Ramesh Khanna:

    Hi Ramesh,

      Thanks for your rapid reply!  I look forward to your updates.


  • In reply to Patrick Cruce57:

    Hello Pat,

    Sorry for the delay in getting back to you. Here is the information:

    For external clock synchronization, a resistor connected to the RT pin is required as shown in the datasheet. Therefore, at power-up, the device will switch at the frequency set by the RT resistor (it could be anything between 100k and 1M). The SYNC pin will be in listening mode for about 20us and then if no external clock is present, the device will keep switching at that frequency. If the external clock is provided after 20us, it will overwrite the running frequency and disable the oscillator internally. The only caveat here is that after the oscillator is disabled and if for whatever reason the external clock is no longer provided, the device will not go back to using the internal oscillator.

    In short, you can provide an external clock to synchronize the device after 20us.