Fujitsu MB39A104 manual ESR ≤ ΠfC L 050 491

MB39A104

• Smoothing Capacitor

The smoothing capacitor is an indispensable element for reducing ripple voltage in output. In selecting a smooth- ing capacitor it is essential to consider equivalent series resistance (ESR) and allowable ripple current. Higher ESR means higher ripple voltage, so that to reduce ripple voltage it is necessary to select a capacitor with low ESR. However, the use of a capacitor with low ESR can have substantial effects on loop phase characteristics, and therefore requires attention to system stability. Care should also be taken to use a capacity with sufficient margin for allowable ripple current. This application uses the (OS-CON TM) 6SVP82M made by Sanyo. The ESR, capacitance value, and ripple current can be calculated from the following formulas.

Equivalent Series Resistance : ESR

ESR ≤ ΔVO − 1

ΔIL 2πfCL

Capacitance value : CL

ΔIL

CL ≥ 2πf (ΔVO − ΔIL ⋅ ESR)

Ripple current : ICLrms (VIN − VO) ton

ICLrms ≥

2√3L

Example: Using the 6SVP82M

Rated voltage = 6.3 V, ESR = 50 mΩ, maximum allowable ripple current = 1570 mArms

Equivalent series resistance

CH1		ΔVO
ESR ≤			−	1
		ΔIL		2πfCL
≤	0.050		−	1
		0.491		2π ⋅ 500 ⋅ 103 ⋅ 82 ⋅ 10−6

≤98.0 mΩ

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