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LMR16006: If we select output inductor less than calculating as datasheet, what will it affect with?

Gumpol Gorjarernrut
Prodigy 40 points
Part Number: LMR16006

Due to we want to common old design and we don't change component (New design difference only output current, we reduce to 38mA)

After we re-calculate, we found output inductance should more than 314uH (follow equation 1, on page 12 of LMR16006 datasheet). but we want to use 47uH (common old design).

please you check us that we can use this value with condition below? What will it affect with?

we try to calculate ESR of capacitor (follow Equation 8,page 13 of LMR16006 datasheet), we get 0.6 Ohm and we use 0.03 Ohm.

Our condition

Input voltage: 48 V (45.6 to 50.4V)

Output voltage: 3.6V 

Maximum output current: 0.038A

Switching Frequency: 700kHz

Component selection

output inductance: 47uH (tolerance 10%)

output capacitance: 10uF/6.3V (ESR 0.03 Ohm at 700kHz)

Calculation

Ripple current: 0.112 A (follow equation 2, on page 12 of LMR16006 datasheet)

Output capacitor: 1.5uF (follow equation 5, on page 13 of LMR16006 datasheet)

Output capacitor: 0.26uF (follow equation 6, on page 13 of LMR16006 datasheet)

Output capacitor: 0.28uF (follow equation 7, on page 13 of LMR16006 datasheet)

R(ESR) : 0.637 Ohm (follow equation 8, on page 13 of LMR16006 datasheet)

Our circuit

ESR of Capacitor

  • 0
    TI__Mastermind 28400 points

    Hello,

    Calculating for the output inductor for minimizing its corresponding value while ensuring stability should be done at max loading for the device :ie 600mA.

    In addition, your output capacitor calculations were done for corresponding output ripple and load transient. OFten for the given application specification, these would determine the actual capacitance needed to ensure this specification is met, as well, guarantee stability. In this case, the value calculated is most likely insufficient for stability. I would advise staying with your current capacitor, or, if looking to reduce, ensure at least 10uF ceramic capacitor is used.

  • 0 in reply to Marshall_Beck
    Prodigy 40 points

    Dear Marshall,

    Thank you for your reply.

    after I read your suggestion, I have question as below

    1. I still confuse that can I use output inductance 47uH with load 0.038A? what will it affect with?

    2. For output capacitor suitable with our design, you mean I should output capacitor least 10uF, right?

    Best regard,

  • +1 in reply to Gumpol Gorjarernrut
    TI__Mastermind 28400 points

    Hello Gumpol,

    It is good to help you out.

    1. 47uH would be suitable to use. It will be optimized for reasonable solution size, stabilility, and output ripple.

    2. Yes, please use 10uF ceramic output capacitor, or more. Current electrolytic capacitor is sufficient.