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LM20333: Settling time

Danilo A.
Mastermind 25485 points
Part Number: LM20333
Other Parts Discussed in Thread: LM20133, TPS54350

Hi Team,

Our customer needs a synchronous DC/DC converter with frequency synchronization from external source. The LM20133, LM20333 and TPS54350 seem fit for his application, however, there are no information in the datasheets regarding the settling time of the devices (probably due to the internal PLL), when the external sync frequency is changed (NOT at startup).

According to our customer, in his application, the external frequency could be changed very often, while the component is regulating power. He needs to know how the component will behave when the SYNC frequency is being changed.

Is there any data on how long it takes for the component to settle when the SYNC frequency is changed? Or is this something that he have to determine by bench-testing? It seems like it is not a typical scenario for a synchronous DC/DC converter.

Regards,

Danilo

  • 0
    TI__Mastermind 30430 points

    Hello Danilo,

    The LM61430 would be the preferred device for this application.

    From my experience with this device, alternating from external sync source to internal clock source is a pretty seamless transition to the outside user.

    It is recommended to evaluate on the EVM to ensure the performance is adequate for the customer application circuit,

  • 0 in reply to Marshall_Beck
    TI__Mastermind 25485 points

    Hi Marshall,

    Thank you for your response. According to our customer,

    Perhaps I'm just not explaining this adequately. I'll give an example: I'm providing the converter with a synchronizing signal at 300 kHz. While keeping the converter powered up and operating, I want to change to 350kHz, then later to 500kHz, then later to 750kHz, then to 375kHz, then to 1Mhz. Will this work? And if so, how long does it take for the converter to settle after each one of those frequency changes? Since it uses an internal PLL, I can't imagine there not being required time for the PLL to re-synchronize to each frequency change.

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Mastermind 30430 points

    hello Danilo,

    The device supports frequency hopping if it is within the recommended operating condition for sync frequency.

    This would be no different I feel than the case I mentioned earlier (switching between internal and external clock source). From the experience I have with our particular devices, the effect is negligible on the output. Given the corresponding switching frequency period in which we sample, this is why I feel this to be the case.