JAJSPV2 データシート

JAJSPV2 august 2023 TPSM8S6C24

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）

MOY|45
- MPQF759

サーマルパッド・メカニカル・データ

発注情報

jajspv2_oa

9.2.2.5.1 Output Voltage Ripple

The output-voltage ripple is the second criterion for output capacitor selection. Use Equation 14 to calculate the minimum output capacitance required to meet the output-voltage ripple specification.

Equation 14.

C_{O U T (m i n)} = \frac{I_{R I P P L E}}{8 \times f_{s w} \times V_{O U T (R I P P L E)}} = \frac{7.7 A}{8 \times 650 k H z \times 10 m V} = 148 µ F

In this case, the target maximum output-voltage ripple is 10 mV. Under this requirement, the minimum output capacitance for ripple is 148 µF. This capacitance value is smaller than the output capacitance required for the transient response, so select the output capacitance value based on the transient requirement. Considering the variation and derating of capacitance, in this design, 2 x 330-µF low-ESR tantalum polymer bulk capacitors and 9 x 100-µF ceramic capacitors were selected to meet the transient specification with sufficient margin. Therefore the selected nominal C_OUT is equal to 1560 µF.

With the output capacitance value selected the ESR must be considered. This is an important consideration in this example because it uses mixed output capacitor types. First use Equation 15 to calculate the maximum allowable impedance for the output capacitor bank at the switching frequency to meet the output voltage ripple specification. Equation 15 indicates the output capacitor bank impedance must be less than 1.3 mΩ. The impedance of the ceramic capacitors is calculated with Equation 16 and the impedance of the bulk capacitor is calculated with Equation 17. The result from Equation 17 shows the impedance of the bulk capacitor at the switching frequency is dominated by its ESR. Equation 18 calculates the total output impedance of the output capacitor bank at the switching frequency to be 0.25 mΩ which meets the 1.3 mΩ requirement.

Equation 15.

Z_{O U T (M A X)_f_{S W}} = \frac{V_{O U T (R I P P L E)}}{I_{R I P P L E}} = \frac{10 m V}{7.7 A} = 1.3 m Ω

Equation 16.

Z_{C E R_f_{s w}} = \frac{1}{2 π \times f_{s w} \times C_{C E R}} = \frac{1}{2 π \times 650 k H z \times (9 \times 100 μ F)} = 0.27 m Ω

Equation 17.

Z_{B U L K_f_{s w}} = \sqrt{{E S R}_{B U L K}^{2} + {(\frac{1}{2 π \times f_{S W} \times C_{B U L K}})}^{2}} = \sqrt{{(\frac{6 m Ω}{2})}^{2} + {(\frac{1}{2 π \times 650 k H z \times (1 \times 2x330 μ F)})}^{2}} = 3.02 m Ω

Equation 18.

Z_{C O U T_f_{s w}} = \frac{Z_{C E R_f_{s w}} \times Z_{B U L K_f_{s w}}}{Z_{C E R_f_{s w}} + Z_{B U L K_f_{s w}}} = \frac{0.27 m Ω \times 3.02 m Ω}{0.27 m Ω + 3.02 m Ω} = 0.25 m Ω