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LMQ66410-Q1: LMQ66410-Q1 component selection

Rakshitha K
Prodigy 20 points
Part Number: LMQ66410-Q1

Tool/software:

Hi Team,

We are currently using the LMQ66410-Q1 part in our design. our requirement are as follows

  Vin = 12V , Vout =1.2V , Output current = 1A

  • We have simulated this part using  WEBENCH and also performed manual calculation based on the formula provided in the datasheet. However, we noticed difference between the component values generated by the  WEBENCH and those calculated manually, particularly with the inductor value (we are disregarding the feedback resistors because their values depend on the  initially assume Rfbt value used to calculate the other resistor Rfbb)
  • Additionally , the datasheet only provides guidance for selecting the output capacitor for 3.3 and 5v output configuration. for the other output voltages, including 1.2V, the datasheet suggests using the  WEBENCH for selecting the input and output capacitor. However, given that the inductor value from WEBENCH differs from our manual calculation, we are unsure whether we should proceed with the WEBENCH generated capacitor values. 

We have attached image of both the WEBENCH generated component values and our manually calculated values for your reference. Could you please advise us on which approach we should follow?

Regards

Rakshitha.K

  • 0
    TI__Guru 72035 points

    Hello

    It looks like your inductance calculation is the same between Webench and hand calc.

    The output capacitance appears somewhat small for a 1.2Vout.

    I will contact the Applications engineers for this device and see if we have some kind of simulation model.

    Thanks

  • 0 in reply to Frank De Stasi
    TI__Mastermind 24115 points

    Hi Rakshitha,

    Webench should be able to provide some stability parameters for your application. You can also modify the webench design to your calculated parameters if you desire by clicking on the part in the design and selecting the "choose alternative" and then the "create custom part" button:

    Here are the stability calculations I found with different inductor values:

    L = 2uH: PM = 70.15deg, GM = -25.9dB, Crossover frequency = 117.36kHz

    L = 2.4uH: PM = 68.64deg, GM = -26.58 dB, Crossover frequency = 117.04kHz

    Webench should give good enough guidelines to get you started with your design. As always we recommend that the design is also tested on the bench to ensure that the performance of the device is up to par with the requirements of the application. Should there be any discrepancy there, we would be more than happy to work with you on this going forward.

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 20 points

    Hi 

    Could you please confirm whether the Circuit operates fine with the specified parameter.

    Regards

    Rakshitha.K

  • 0 in reply to Rakshitha K
    TI__Mastermind 24115 points

    Hi Rakshitha,

    I believe your top and bottom feedback resistors are switched.

    Otherwise, if from the notes above webench shows a stable design, then your application should be ok.

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 20 points

    Hi Joshua , 

    Thanks for the confirmation.

    Yes in our design top and bottom feedback resistors are switched.

  • 0 in reply to Rakshitha K
    TI__Mastermind 24115 points

    Hi Rakshitha, 

    Sounds good. Happy to help!

    Thank you,

    Joshua Austria