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LMR14010a

Stephen Kertesz
Prodigy 90 points
Part Number: LMR14010A

Regarding Eco-mode - I have a Vin of 6-9V, Vout of 5V, Iload of 50mA-600mA.

Light load conditions would be less than 5mA.

Can you tell me how the inductance value effects Eco-mode operation?

Inductance of 12uH:
Will the LMR14010A go into Eco-mode at less than 5mA?
What load value will result in exiting Eco-mode?

Inductance of 22uH:
Same questions

Inductance of 47uH:
Same questions

Thank you.

  • 0
    TI__Mastermind 30430 points

    Hello, eco mode is engaged by peak inductor current. The value of the peak inductor current tends to be 10-30% of the device max rated DC current ie: 1A.

    With larger inductance, the device will go into ECO mode at a higher DC load current in comparison to a smaller inductance.

    5mA load current you will be in ECO mode, as well, be in discontinuous mode of operation.

    The LMR14010A operates in Eco-modeTm at light-load currents to improve efficiency by reducing switching and gate drive losses. For Eco-modeTm operation, the LMR14010A senses peak current, not average or load current, so the load current where the device enters Eco-modeTm is dependent on VIN, VOUT and the output inductor value. When the load current is low and the output voltage is within regulation, the device enters Eco-modeTm (see Figure 12) and draws only 28-µA input quiescent current.

  • 0
    Prodigy 90 points

    Thanks for the info.

    I have an inductor value of 47uH (which I believe is too high) and I don't believe the device is going into Eco-mode as the waveforms don't match Fig 12, higher freq switching going on and the current draw is higher than expected.

    I thought the high value of 47uH might be the cause of not going into Eco-mode but you're saying that this value would engage Eco-mode at higher load current?

    At what load would the device exit Eco-mode?

  • 0 in reply to Stephen Kertesz
    TI__Mastermind 30430 points

    Do you have waveforms that I can review? I would be interested in seeing the VSW and IL waveform.

    It might be good to verify that device goes into eco mode by removing the load and observing when it exits with an eload or a variable load.

    What are the power conditions (vin, vout) for the testing you are performing? That will help me answer your question.

  • 0
    Prodigy 90 points

    I am in the process of doing just that, removing the load and replacing with variable load.
    It's a very small design so it's a process.
    No load current draw is 78uA at 8Vin so it looks like it might be in Eco-mode with no load.

    Power conditions are Vin = 8V, Vout = 5V.

    I am also simulating in Webench, which is telling me that my 47uH is exceeding the recommended limits of 11.9uH - 35.71uH.
    The Webench sim chose 12uH.
    Is my 47uH too high?

  • 0 in reply to Stephen Kertesz
    Prodigy 90 points

    I couldn't remember why I initially chose 47uH but then pulled up an old sim and saw that value was recommended for high efficiency.
    Would like to keep it if no good reason to change.

  • 0 in reply to Stephen Kertesz
    TI__Mastermind 30430 points

    Hello Stephen, webench is giving you that range most likely for 20-30% inductor current ripple, which is the naïve thing to do.

    47uH should be satisfactory for stability, as well, reasonable output ripple.

    A higher inductance reduces pk2pk inductor current ripple. AC losses are quite small for these powder iron core inductor often utilized in low power dcdc converter, thus, designers often tend to select an inductor whose inductance allows for 30% ripple at the device recommended max DC load current at the design's nominal vin.

  • 0
    Prodigy 90 points

    Thanks again for taking the time to consider.
    I have since found the component responsible for the higher than expected current draw at no load and the supply seems to be working as intended.
    I am still setting up to observe the LMR14010A go in and out of Eco-mode though I think I am in good shape.

    Could you provide more details on your earlier statement regarding higher inductance resulting in the device going into Eco-mode at higher load?
    The board is battery powered with a very low duty cycle, maybe 80% of the time it'll be drawing 300uA or so.
    During normal operation it'll draw 10-50mA with peaks of 400-600mA.
    How does 12uH vs 22uH vs 47uH affect opeartion and its ability to go in/out of Eco-mode?

  • 0 in reply to Stephen Kertesz
    TI__Mastermind 30430 points

    Eco mode is triggered by peak inductor current.

    Per the design, when it falls below apx 150mA, then device will begin to reduce switching freq.

    Peak inductor current is delta iL/2 + DC load current

    Eq9 in link below for delta iL calc

    Inductor (L) dictates delta iL...inversely proportional

    www.ti.com/.../lmr14030.pdf

  • 0
    Prodigy 90 points

    Thanks.

    I finally get it.