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Original question:

TPS61378-Q1: inductor selection

TPS61378-Q1: TPS61378-Q1: inductor selection

Sourav S Kashyap
Prodigy 40 points
Part Number: TPS61378-Q1

Following is the requirement in my application:

  • Input Voltage: 2.3V to 4.1V
  • Output Voltage: 5.5V
  • Maximum Output Current (Maximum Load Current): 0.6A

When ripple percentage is considered around 40 percent of Input current, the ripple current will not fall in the recommended range (0.8A to 2A) for certain load currents. How to size the inductor in such a scenario?

  • 0
    TI__Genius 16325 points

    Hi Sourav,

    the inductance could be 0.68uH and the ripple current will be around 1A.

    Please refer to the calculation tool.

    5672.TPS61378 Calculation Tool V1.1.xlsx

  • 0 in reply to Fergus He
    Prodigy 40 points

    As per the above equation, ripple current is independent of load current and input current. Then irrespective of the load current, will the ripple current remain the same?

    But the ripple current has dependency on load current in the above equation. Could you please explain the usage of these equations with example?

    If the ripple current depends on load current, having 0.68uH inductor will result in ripple current that do not fall in the recommended range, say for medium load. Please let me know if any of my understanding is wrong.

  • +1 in reply to Sourav S Kashyap
    TI__Genius 16325 points

    Hi Sourav,

    The two equations are both right.

    First one is the used to calculate the value, and the second is to design when you do not have an inductor value.

    The design steps are as below:

    1. design the delta I due to the max input current.

    Usually, we choose the ripple current be specific proportions of the max input current to ensure a best use of inductor.

    If the ripple is small, then the inductance will be large and cost will be high; if the ripple is large, then the loss will increase and influence efficiency.

    So, usually we choose 20% to 50% ripple percentage.

    For TPS61378-Q1, it has a ripple current demand of 0.8 to 2A, you need to combine these two.

    2. after choosing the ripple current, we can choose the inductor, when working, the ripple is independent of load current.

    For 0.68uH is a commonly used value, you can check 1uH and 0.47uH.

    1uH causes the ripple small than 0.8A and 0.47uH causes the ripple too large.

    Hope your question be solved.

    Best Regards

    Fergus