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LM22670-5.0 FOR OUTPUTS HIGHER THAN 5V

Ran Feldman
Intellectual 780 points
Other Parts Discussed in Thread: LM22670

Hello,

 

Looking in the Webench, the LM2267x calculator and the data sheet on page 12: “The internal compensation of the -ADJ option is optimized for output voltages below 5V. If an output voltage of 5V or greater is needed, the -5.0 option with an external resistor divider can be used.”

 

Can you explain 3 things:

 

  1. What will be the switching frequency in the self-synchronization mode?
  2. How are the feedback resistors being calculated when using the -5.0 version?
  3. Is this correct and the –ADJ version cannot be used due to lack of internal compensation?

 

Thanks,

Ran

  • 0
    TI__Expert 3870 points

    Hi Ran,

    Here are the answers to your questions:

    1) The switching frequency will be commanded by the highest set regulator frequency: You need to select one of the regulators as the master clock.  Please keep in mind that in order for the Sync function to work the external clock frequency (in this case, the frequency of the regulator set as the master clock) needs to be much higher than the default set frequency of 500 kHz (typ).

    2) What VOUT do you need to use? Is it close to 5.0V or much higher than >>5.0V?  If it's much higher than >> 5.0V then use the following equation to calculate the resistor divider (pg 16 of LM22670 datasheet):

    3) Yes, the Adj version internal loop compensation has been set for output voltages in the 1.285V and 5.0V range.  So for VOUT >> 5.0V then use the 5.0V as stated above in #2.

    Best Regards,

    -Juan