LTM4626 operating frequency setting

Hello,

I don't unterstand the how to calculate Rfset to modify operating frequency.

The datasheet gives with Rset connected between FREQ and GND :

Does it mean 274KOhm in parallel with Rfset ?

An other point is : on eval board, FREQ pin can be connected  with a resistor to GND and another to INTVCC.

What is the function of the resistor between FREQ and INTVCC ?

Best regards

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  • Hello,

    the frequency is dependent from the voltage at Pin FREQ (page 4, sorry for bad resolution) :

    So a direct connection between INTVCC and FREQ ends up with the highest possible frequency.

    The sign in the formula does stand for parallel connection, your assumption is correct.

    kind regards

    Markus

  • Thanks for this answer.

    On LTM4626 datasheet availables in Analog web site (rev B), I don't have this table. Is there another version of datasheet ?

    And what is the maximim frequency ? 800KHz or 3MHz ?

    Best regards.

  • Hello Victor,

    sorry, but it looks like I ended up in the wrong datasheet due to a typo(LTM4628). Now I doublechecked that I look in the LTM4626 datasheet:

    Maximum frequency is 3MHz, any frequency higher than nominal 600kHz has to be programmed with a resistor between FREQ and GND with the given formula, so far so good.
    I do not see a reason why the resistor R12 between FREQ pin and INTVC should be equipped, the only mentioned way to change the frequency is a resistor towards GND.

    My assumption would be the max frequency of 3MHz is selected when FREQ pin is pulled high.

    Sorry again for the possible confusion!

    kind regards

    Markus

Reply
  • Hello Victor,

    sorry, but it looks like I ended up in the wrong datasheet due to a typo(LTM4628). Now I doublechecked that I look in the LTM4626 datasheet:

    Maximum frequency is 3MHz, any frequency higher than nominal 600kHz has to be programmed with a resistor between FREQ and GND with the given formula, so far so good.
    I do not see a reason why the resistor R12 between FREQ pin and INTVC should be equipped, the only mentioned way to change the frequency is a resistor towards GND.

    My assumption would be the max frequency of 3MHz is selected when FREQ pin is pulled high.

    Sorry again for the possible confusion!

    kind regards

    Markus

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