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LMR36506: LMR36506 Input Current

JinYong Kim
Prodigy 10 points
Part Number: LMR36506

Tool/software:

in LMR36506 Datasheet, I can calculate the Iq_vin like this Fomula.

I use Vin  = 40V. I can't Find the That Spec in Datasheet. There are Only Vin 13.5V & 24V Spec.

So Can you let me know about That Spec in Vin = 40V.

  • 0
    Prodigy 10 points

    I use Vout adjustable Spec

  • 0 in reply to JinYong Kim
    TI__Genius 9640 points

    Hi JinYong,

    If you are using adjustable output, Ibias is drawn internally from Vin and it shows up in Iq. Unfortunately, we do not have a spec for Iq at Vin = 40V but, looking at IQ_13p5_Adj and IQ_24p0_Adj, there does not seem to be much difference with Vin. So you can consider the same estimate, 22 uA (or +20% for margin), for Iq.

    Now, if EN is connected using a resistor divider to Vin, it will draw a current I_EN = Vin/(sum of enable resistors). If it is directly connected to Vin, the leakage current would be in nA and negligible

    When using adjustable output, the current taken by feedback resistors also comes into play. This can be calculated as I_FB = Vout/(sum of feedback resistors).

    Finally, you can estimate Iq_VIN = Iq +  I_EN + I_FB*Vout/(eff * Vin)

    Regards,

    Niranjan

  • 0 in reply to Niranjan Nair
    Prodigy 10 points

    I have additional questions.

    If the output is small, such as tens of uA, I would like to ask whether it is okay to consider it as an open loop state as mentioned above and perform the same calculation.

  • 0 in reply to JinYong Kim
    TI__Genius 9640 points

    Hi JinYong,

    There are two things

    1) Iq taken strictly by the device only : This is the baseline current (non-switching) consumed by the internal blocks and will stay relatively constant across Vin and load conditions. This is the ~22 uA given in the datasheet as  IQ_13p5_Adj/IQ_24p0_Adj. Please note this is not the total current drawn from input.

    2) Current drawn from input : At no load, the current drawn from input can be estimated like I mentioned in the first answer

    But when a load is applied, even at 10 uA, the device starts switching and the input current calculation is difficult. I would suggest using Webench (webench.ti.com/.../switching-regulator if you want an estimate of input current at a particular condition.

    Regards,

    Niranjan