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LMR62014 simple switcher- External resistor issue

Sharon George
Prodigy 10 points
Other Parts Discussed in Thread: LMR62014

Hi,

I am currently designing a circuit using LMR62014 to generate an output of 14V using a 12V input.

As per the datasheet recommendations, i have calculated the external resistor value to be 810K Ohms to generate an output of 14V using the formula given (R1=R2*(Vout/1.23-1) where, R2=13.3K, Vout=14V as per the recommendations provided).

When i try to simulate the same circuit using the TI online tool "webench" , the circuit is the same except for the external resistor value which is now 170K Ohm.

I tried simulating the circuit with both the resistor values and i get an output of 22V when i use the recommended resistor value which is 810K Ohm and I get 14V when I use the webench suggested circuit i.e. 170K Ohm resistor.


Can you be suggest me on which should I follow? Follow the datasheet recommendations or the circuit given by TI WEBENCH??

I have attached both the simulated circuits with this mail, Kindly have a look.webench_esim_LMR62014.pdfwebench_esim_LMR62014_Datasheet recommendation.pdf

Thanks in Advance!

  • 0
    TI__Guru 72845 points

    The equation should be as follows:  R1 = R2*((Vout/1.23)-1)

    This will give you a value of 138k for R1 with R2=13.3k.

    I am not sure why Webench gave the value of 170k.

    I will pass this to the Webench team.

  • 0
    TI__Intellectual 1825 points

    Hi Sharon,

    As Frank previously mentioned, if Vout=14V and R2=13.3K, R1 should be around 138k.  You can go ahead and follow the WEBENCH design, since it says the top feedback resistor is 140k.

    If you have any other questions or concerns, please let me know.

    Best Regards,
    Jonathan Arzadon
    Applications Engineer
    WEBENCH Designer Center
    Texas Instruments