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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

8.2.2.5 Input Capacitors

The TPS54531 device requires an input decoupling capacitor and, depending on the application, a bulk input capacitor. The typical recommended value for the decoupling capacitor is 10 μF. A high-quality ceramic type X5R or X7R is recommended. The voltage rating must be greater than the maximum input voltage. A smaller value can be used as long as all other requirements are met; however 10 μF has been shown to work well in a wide variety of circuits. Additionally, some bulk capacitance can be required, especially if the TPS54531 circuit is not located within about 2 inches from the input voltage source. The value for this capacitor is not critical but must be rated to handle the maximum input voltage including ripple voltage, and must filter the output so that input ripple voltage is acceptable. For this design two 4.7-μF capacitors are used for the input decoupling capacitor. The capacitors are X7R dielectric rated for 50 V. The equivalent series resistance (ESR) is approximately 2 mΩ and the current rating is 3 A. Additionally, a small 0.01 μF capacitor is included for high frequency filtering.

Use Equation 6 to calculate the input ripple voltage.

Equation 6.

∆ V_{I N} = \frac{I_{O U T (M A X)} \times 0.25}{C_{B U L K} \times F_{S W}} + (I_{O U T (M A X)} \times {E S R}_{M A X})

where

I_OUT(MAX) is the maximum load current
C_BULK is the bulk capacitor value
F_SW is the switching frequency
ESR_MAX is the maximum series resistance of the bulk capacitor

The maximum RMS ripple current must also be checked. For worst case conditions, use Equation 7 to calculate the maximum-RMS input ripple current, I_CIN(RMS).

Equation 7.

I_{C I N (R M S)} = \frac{I_{O U T (M A X)}}{2}

In this case, the input ripple voltage is 243 mV and the RMS ripple current is 2.5 A.

Note:

The actual input voltage ripple is greatly affected by parasitics associated with the layout and the output impedance of the voltage source.

The actual input voltage ripple for this circuit is listed in Table 8-1 and is larger than the calculated value. This measured value is still below the specified input limit of 300 mV. The maximum voltage across the input capacitors is V_IN(MAX) + ΔV_IN / 2. The selected bulk and bypass capacitors are each rated for 50 V and the ripple current capacity is greater than 3 A, both providing ample margin. The maximum ratings for voltage and current must not be exceeded under any circumstance.