Fujitsu MB39A105 manual 2LV O

Page 21

MB39A105

Example:

L

VIN (Max)

2

ton

 

 

 

2IOVO

 

 

 

 

 

 

 

 

 

 

 

42

 

 

94

1

2 0.25 9

9

500 103

3.95 H

Inductance values derived from the above formulas are values that provide sufficient margin for continuous operation at maximum load current, but at which continuous operation is not possible at light loads. It is therefore necessary to determine the load level at which continuous operation becomes possible. In this application, the Sumida CMD5D13-6R8 is used. At 6.8 H, the load current value under continuous operating conditions is determined by the following formula.

Load current value under continuous operating conditions : IO

IO

VIN (Max) 2

 

 

 

 

 

ton

 

 

 

 

 

 

 

 

 

 

2LVO

 

 

 

 

42

 

94

1

2 6.8 106 9

9

500 103

145.2 mA

To determine whether the current through the inductor is within rated values, it is necessary to determine the peak value of the ripple current as well as the peak-to-peak values of the ripple current that affect the output ripple voltage. The peak value and peak-to-peak value of the ripple current can be determined by the following formulas.

Peak value : IL

IL

 

VO IO

+

 

VIN

ton

ton =

VO VIN

t

 

VIN

 

2L

VO

 

 

 

 

 

 

 

 

Peak-to-peak value : ΔIL

 

 

 

 

 

ΔIL

=

 

VIN

ton

 

 

 

 

 

 

 

 

L

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Example: Using the CMD5D13-6R8

6.8 H (allowable tolerance ±20%) , rated current = 1.4 A

Peak value:

IL

 

VO IO

+

 

 

VIN

 

ton

ton =

 

VO VIN

t

 

VIN

 

 

2L

 

 

 

VO

 

 

 

 

 

 

 

 

 

 

 

 

 

9 0.25

 

+

 

 

2.4

(9 2.4)

1

 

 

2.4

 

 

2 6.8

106 9

 

 

500 103

1.20 A

21

Image 21
Contents Features DescriptionPackage PIN Assignment PIN Description Pin No Symbol DescriptionsBlock Diagram Parameter Symbol Condition Value Unit Min Typ Parameter Symbol Condition Rating Unit Min MaxAbsolute Maximum Ratings Recommended Operating ConditionsElectrical Characteristics ParameterPin Conditions Value Unit Min Typ Max Error Typical CharacteristicsTriangularwave oscillation Power Dissipation vs. Ambient Temperature Functions Error amplifier block Error Amp1, Error Amp2Triangular-wave oscillator block OSC PWM comparator block PWM CompTimer-latch short-circuit protection circuit SCP PowerUnder voltage lockout protection circuit Uvlo Short-circuit protection detection output functionSetting 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 Ordering Information Usage PrecautionDo not apply negative voltages Part number Package RemarksIndex Package DimensionFujitsu Limited