米6体育平台手机版

ZHCSM29A September 2023 – June 2024 LM70840-Q1 , LM70860-Q1 , LM70880-Q1

PRODUCTION DATA

请参考 PDF 数据表获取器件具体的封装图。

机械数据 (封装 | 引脚)

RRX|29

散热焊盘机械数据 (封装 | 引脚)

8.2.1.2.5 Output Capacitors

Use Equation 36 to estimate the output capacitance required to manage the output voltage overshoot during a load-off transient (from full load to no load) assuming a load transient deviation specification of 5% (250mV for a 5V output).
Equation 36. $C_{O U T} \geq \frac{L_{O} \times Δ I_{O U T}^{2}}{{(V_{O U T} + Δ V_{O V E R S H O O T})}^{2} - V_{O U T}^{2}} = \frac{3.3 µ H \times {(8 A)}^{2}}{{(5 V + 250 m V)}^{2} - {5 V}^{2}} = 82 µ F$
Noting the voltage coefficient of ceramic capacitors where the effective capacitance decreases significantly with applied voltage, select four 47µF, 10V, X7S, 1210 ceramic output capacitors. Generally, when sufficient capacitance is used to satisfy the load-off transient response requirement, the voltage undershoot during a no-load to full-load transient is also satisfactory.
Use Equation 37 to estimate the peak-peak output voltage ripple at nominal input voltage.
Equation 37. ${Δ V}_{O U T} = \sqrt{{(\frac{Δ I_{L O}}{8 \times F_{S W} \times C_{O U T}})}^{2} + {(R_{E S R} \times Δ I_{L O})}^{2}} = \sqrt{{(\frac{3.2 A}{8 \times 400 k H z \times 82 µ F})}^{2} + {(1 m Ω \times 3.2 A)}^{2}} = 12.6 m V$
where
- R_ESR is the effective equivalent series resistance (ESR) of the output capacitors.
- 82µF is the total effective (derated) ceramic output capacitance at 5V.
Use Equation 38 to calculate the output capacitor RMS ripple current using and verify that the ripple current is within the capacitor ripple current rating.
Equation 38. $I_{C O (R M S)} = \frac{Δ I_{L O}}{\sqrt{12}} = \frac{3.2 A}{\sqrt{12}} = 0.92 A$