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ZHCSB15B May 2013 – October 2023 TPS54531

PRODUCTION DATA

封装选项

机械数据 (封装 | 引脚)

DDA|8
- MPDS092F

散热焊盘机械数据 (封装 | 引脚)

DDA|8
- PPTD058I

订购信息

8.2.2.6.1 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} \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}}

where

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 = 0.3 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 as 4.8 μH. For this design, a close, standard value was chosen: 4.7 μH.

For the output filter inductor, do not exceed the RMS current and saturation current ratings. Use Equation 9 to calculate the inductor ripple current (I_RIPPLE).

Equation 9.

I_{R I P P L E} = \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}

Use Equation 10 to calculate the RMS inductor current.

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}}

Use Equation 11 to calculate the peak inductor current.

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 5.03 A and the peak inductor current is 5.96 A. The selected inductor is a Wurth 4.7 μH. This inductor has a saturation current rating of 19 A and an RMS current rating of 7 A, which meets these requirements. Smaller or larger inductor values can be used depending on the amount of ripple current the designer wants 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 TPS54531 device are in the range of 1 μH to 47 μH.