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TPS56637: Recommended inductor value and inductor current rating

Taketo Sato
Genius 9745 points
Part Number: TPS56637

Hello team,

I am considering 24Vin, 5Vout, 3.2A with TPS56637 and I have questions.

  • TPS56637 datasheet table 4 shows recommended component values.
    I think the recommended values are for stability purpose to keep LC double pole location within optimal range.
    Can we use different inductor value from the table recommendation if we keep L x C range?
    For example 5Vout case, datasheet recommends 3.3uH and 20uF(min) to 100uF(max)  as output LC.
    Can we use 10uH and 20uF which is within L x C range for 5Vout with lower ripple current?
  • In case calculated peak current is about 3.6A, is an inductor with 5.8A current rating good choice? or should we use an inductor that support higher rating than current limit(8.6A max)?

Best regards,

  • +1
    TI__Expert 5030 points

    Hi Taketo,

    1. Yes. For loop stability, keeping L*C in the same range of the recommended L and C is OK. But selecting large L and smaller C would harm the load transient performance. So need to make sure that could satisfy the application requirement.

    Another point is that if device works in FCCM mode, there could be negative current when output voltage is pulled high with external source and could possibly trigger negative OC (NOC). Smaller inductor current ripple could cause the risk for damaging when NOC is triggered. If device works in ECO mode, there's no risk for this. If device needs to work in FCCM mode, please check the loading feature and make sure the loading doesn't have bi-directional power and won't source power to converter.

    2. Recommend to keep saturation current of inductor to be higher than DC current limit. The given current limit in datasheet is inductor valley current, so adding 1/2 inductor current pk-pk ripple on the given current limit, it's the DC current limit. Recommend to keep the saturation current rating of inductor to be larger than this DC current limit.

    Thanks,

    Andrew