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LM5026EVAL: SYNC Pin & Output Caps

Irene Perez
Prodigy 150 points
Part Number: LM5026EVAL
Other Parts Discussed in Thread: LM5026, LM5025

Hi,

I have a couple of question regarding the evaluation board and performance of the LM5026 controller:

1-) I tried to SYNC to an external frequency clock directly applying a pulsed signal (Sync pulse width > 15ns, Sync threshold: 1V-2V, higher freq than free running freq set by RT) through a resistor(to limit the current) directly to J3(SYNC1). This procedure does not work. I have done this into the LM5025 and works, is there any difference between these two controllers regarding the SYNC option?

Datasheet of LM5026 recommends an open drain output for the interface between LM5026 and the external clock, but is it mandatory for external SYNC? I would appreciate more info about how the Sync works in this controller.

1-)I would like to know the part number of the output capacitors(C19&C20) of the EVAL board, in the BOM, there is a part number for the ceramic caps(C21-C23: 68uF) and tantalum caps(C19&C20: 330uF), in the EVAL there are not tantalum caps, instead there are another set of ceramic(orange colored) what is the part number of the real C19 and C20?

Many thanks,

  • 0
    TI__Mastermind 34465 points

    Hello Irene,

    The capacitors C19, C20 are actually solid  tantulum capacitor Vishay 594D series.
    The full part number is 594D337X96R3D2T.
    The Kemet part in the BOM is discontinued and this is the replacement part now used .

    You should synchronise the EVAL board by driving J11 with the external sync signal .

    The open drain FET mentioned in the data sheet is Q7  on the EVAL board

    J3 is suitable as a test point or as a connection point if you wish to synchronise multiple EVAL modules.

    Regards

    John

  • 0 in reply to John Griffin1
    Prodigy 150 points

    Great thanks John, second question is clear.

    Regarding first point, I will try the sync through the Q7. But could you please be so kind to explain the diferencies between the SYNC feature of the LM5026 and the LM5025, from the block diagram seems they are the same but they are not. It is important for my application to understand what is behind the sync pin.

    Waiting your update,

    Thanks,

  • 0 in reply to Irene Perez
    TI__Mastermind 34465 points

    Hello Irene,

    You did not explain how you did the test with the LM5025 part.

    Did you use the same pcb and switch between LM5026 and LM5025 ?

    The data sheet explain the requirements for synchronising the parts. The LM5026 is synchronized by pulling SYNC low with an open drain drain directly on the SYNC pin. There is no requirement for a current limiting resistor on SYNC.

    Regards

    John