Fujitsu MB39A105 manual Esr

Page 23

MB39A105

• 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 TEPSLA21A475M8R (NEC/TOKIN) . The ESR, capacitance value, and ripple current can be calculated from the following formulas.

Equivalent Series Resistance : ESR

 

 

 

 

ΔVO

1

 

ESR

 

 

 

 

 

ΔIL

 

2πfCL

Capacitance value : CL

CL

 

 

 

 

 

ΔIL

 

2πf (ΔVO − ΔIL ESR)

Ripple current : ΔICL

ΔICL

 

VIN

ton

 

 

 

L

 

 

 

 

 

 

 

 

Example: Using the TEPSLA21A475M8R (Three piecies are parallel.)

Rated voltage = 10 V, ESR = 500 mΩ, maximum allowable ripple current = 1 App

Equivalent series resistance

ESR

 

ΔVO

 

1

 

 

ΔIL

 

 

2πfCL

 

0.18

 

1

 

0.654

2π ⋅ 500 103 14.1 106

252.7 mΩ

Capacitance value : CL

CL

ΔIL

2πf (ΔVO − ΔIL ESR)

 

0.39

 

2π ⋅ 500 103 (0.18 0.654 0.167)

2.94 F

Ripple current : ΔICL

ΔICL

VIN

 

 

 

ton

 

 

 

 

 

 

L

 

 

4 (9 4)

1

 

 

6.8 106 9

500 103

0.654 App

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Image 23
Contents Package FeaturesDescription PIN Assignment PIN Description Pin No Symbol DescriptionsBlock Diagram Recommended Operating Conditions Parameter Symbol Condition Rating Unit Min MaxParameter Symbol Condition Value Unit Min Typ Absolute Maximum RatingsPin Conditions Value Unit Min Typ Max Electrical CharacteristicsParameter Error Typical CharacteristicsTriangularwave oscillation Power Dissipation vs. Ambient Temperature PWM comparator block PWM Comp Error amplifier block Error Amp1, Error Amp2Functions Triangular-wave oscillator block OSCShort-circuit protection detection output function PowerTimer-latch short-circuit protection circuit SCP Under voltage lockout protection circuit UvloSetting the Triangular Oscillation Frequency Setting the Output VoltageSetting the SOFT-START Times Timer-latch short-circuit protection circuit MB39A105 Equivalent Circuit Application Parts No Parts ListSelection of Components 2I OV O 2LV O Peak-to-peak value ESR Reference Data Part number Package Remarks Usage PrecautionOrdering Information Do not apply negative voltagesIndex Package DimensionFujitsu Limited