JAJS371 データシート

JAJS371D January 2009 – September 2023 TPS54332

PRODUCTION DATA

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）

DDA|8
- MPDS092F

サーマルパッド・メカニカル・データ

DDA|8
- PPTD087E

発注情報

8.2.2.6 Inductor Selection

To calculate the minimum value of the output inductor, use Equation 8.

Equation 8.

L_{M I N} = \frac{V_{O U T (M A X)} \times (V_{I N (M A X)} - V_{O U T})}{V_{I N (M A X)} \times K_{I N D} \times I_{O U T} \times F_{S W} \times 0.8}

K_IND is a coefficient that represents the amount of inductor ripple current relative to the maximum output current. In general, this value is at the discretion of the designer; however, the following guidelines can be used. For designs using low-ESR output capacitors such as ceramics, a value as high as K_IND = 0.4 can be used. When using higher ESR output capacitors, K_IND = 0.2 yields better results.

For this design example, use K_IND = 0.3 and the minimum inductor value is calculated to be 2.48 μH. For this design, a l 2.5-μH inductor is chosen.

For the output filter inductor, make sure that the RMS current and saturation current ratings not be exceeded. The peak-to-peak inductor current is calculated using Equation 9.

Equation 9.

I_{L P P} = \frac{V_{O U T} \times (V_{I N (M A X)} - V_{O U T})}{V_{I N (M A X)} \times L_{O U T} \times F_{S W} \times 0.8}

The RMS inductor current can be found from Equation 10.

Equation 10.

I_{L (R M S)} = \sqrt{I_{O U T (M A X)}^{2} + \frac{1}{12} \times {(\frac{V_{O U T} \times (V_{I N (M A X)} - V_{O U T})}{V_{I N (M A X)} \times L_{O U T} \times F_{S W} \times 0.8})}^{2}}

And the peak inductor current can be determined with Equation 11.

Equation 11.

I_{L (P K)} = I_{O U T (M A X)} + \frac{V_{O U T} \times (V_{I N (M A X)} - V_{O U T})}{{1.6 \times V}_{I N (M A X)} \times L_{O U T} \times F_{S W}}

For this design, the RMS inductor current is 3.51 A and the peak inductor current is 4.15 A. The chosen inductor is a Coilcraft MSS1038-252NX_ 2.5 μH. The inductor has a saturation current rating of 7.62 A and an RMS current rating of 6.55 A, meeting these requirements. Smaller or larger inductor values can be used depending on the amount of ripple current the designer wishes to allow so long as the other design requirements are met. Larger value inductors have lower AC current and result in lower output voltage ripple, while smaller inductor values increase ac current and output voltage ripple. In general, inductor values for use with the TPS54332 are in the range of 1 μH to 47 μH.