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LTM4626 operating frequency setting

Thread Summary

The user asked how to calculate Rfset to modify the operating frequency of the LTM4626 and inquired about the function of a resistor between FREQ and INTVCC. The final answer clarified that the resistor Rfset is connected in parallel with 274kΩ to modify the frequency, and a direct connection between FREQ and INTVCC selects the maximum frequency of 3MHz. The accompanying answer noted that the LTM4626 datasheet (Rev B) does not include the frequency table, and the maximum frequency is 3MHz, not 800kHz.
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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 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

  • thanks for this informations.

    Best regards