LTC7871

When developing a step-down converter based on the LTC7871 chip, a discrepancy was found in the values of the operating frequency, which is indicated in the datasheet in the table ELECTRICAL CHARACTERISTICS page 5 and calculated by the formula page 28.
When the resistor value Rfreq = 27.4 kOhm, the frequency calculated by the formula = 63.372 kHz, according to the table-70 kHz.

Could you please specify which value is correct and under what conditions.
Ideally, we would like to use the Rfreq resistor to set the lowest possible frequency value.

  • 0
    •  Analog Employees 
    on Apr 19, 2021 1:19 PM

    Hello,

    in general the oscillator in a switch mode controller has a tolerance which is not so small. please compare the specified values in the datasheet:

    Resolution of screenshot is lousy, but we have a range from 55kHz up to 85kHz for a certain RT value (27.4k).

    If you need it more accurate than the +-20% you have to feed an external clock to the respective SYNC pin. Details can be found in the datasheet.

    kind regards

    Markus Holtkamp