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Original question:

TPS552882: TPS552882 switching frequency setting

TPS552882: External Clock Synchronization

Akihisa Tamazaki
Genius 10805 points
Part Number: TPS552882

Hello team,

My customer has questions about TPS552882 External Clock Synchronization.
This question is relative to the following E2E forum.
https://e2e.ti.com/support/power-management/f/power-management-forum/971077/tps552882-tps552882-switching-frequency-setting?tisearch=e2e-sitesearch&keymatch=TPS552882#

The customer is using TPS552882EVM-400kHz.   The resister of FSW pin is 49.9kohms, which means 400kHz frequency setting.
In this setting, The customer tried to synchronize TPS552882 with an 400kHz external clock and could do it. After that, they changed the frequency from 400kHz to 300kHz. However TPS552882 could not  be synchronized to an 300kHz external clock. 

In the datasheet, the external clock frequency at the DITH/SYNC pin must have lower than 0.4-V low level voltage and must be within ±30% of
the corresponding frequency set by the resistor.  So 300kHz external clock should be under the TPS552882 specification.

1. Can we change the external frequency from from 400kHz to 300kHz during operation?
2. What percentage of the frequency set by FSW is the external frequency that can be followed during operation?
3. How long can  TPS552882   be synchronized with the external clock after TPS552882 can receive the external clock?

Your advice would be so appreicated.

Best Regards,
Akihisa Tamazaki

  • +1
    TI__Mastermind 34201 points

    Hi Akihisa,

    1. May I know the MODE register resistance on the EVM that customer is using? Please make sure the device is configured working at FPWM mode so that external clock synchronization function works.

    2. TPS552882 should be able to be synchronized to 300kHz. 

  • 0
    TI__Genius 10805 points

    Hello Zack-san,

    Thank you so much for your comment. I will ask the customer the MODE resister resistance.

    Would  you please advise about question3 as below.
    3. How long can  TPS552882   be synchronized with the external clock after TPS552882 can receive the external clock?

    Your advice would be so appreciated.

    Best Regards,
    Akihisa Tamazaki

  • +1 in reply to Akihisa Tamazaki
    TI__Mastermind 34201 points

    Hi Akihisa,

    Please also confirm with customer that they are using our latest RTMed device for test.

    Per my test on bench, TPS552882 could be synchronized to external clock very soon, ~ 50uS.

  • 0 in reply to Zack Liu
    TI__Genius 10805 points

    Hello Zack-san,

    Thank you so much for your comment.

    The customer changed Mode resistance is 0ohms, then confirm that TPS552882 can be synchronized to 300kHz external clock. Thank you for your advice.

    If I receive any further questions from the customer, let me ask you by email directly.

    Best Regards,
    Akihisa Tamazaki