Fujitsu MB39A104 manual Di ≥ I O ⋅ 1

Page 29

MB39A104

• Flyback diode

The flyback diode is generally used as a Shottky barrier diode (SBD) when the reverse voltage to the diode is less than 40V. The SBD has the characteristics of higher speed in terms of faster reverse recovery time, and lower forward voltage, and is ideal for achieving high efficiency. As long as the DC reverse voltage is sufficiently higher than the input voltage, the average current flowing through the diode is within the average output current level, and peak current is within peak surge current limits, there is no problem. In this application the Rohm RB053L-30 is used. The diode average current and diode peak current can be calculated by the following formulas.

Diode mean current : IDi

IDi ≥ IO ⋅ (1 − VO )

VIN

Diode peak current : IDip

IDip ≥ (IO + VO toff) 2L

Example: Using the Rohm RB053L-30

VR (DC reverse voltage) = 30 V, average output voltage = 3.0 A, peak surge current = 70 A, VF (forward voltage) = 0.42 V, IF = 3.0 A

CH1
IDi ≥ IO ⋅ (1 −	VO	)

	VIN

≥3 ⋅ (1 − 0.263)

≥2.21 A

CH2
IDi ≥ IO ⋅ (1 −	VO	)

	VIN

≥3 ⋅ (1 − 0.174)

≥2.48 A

	CH1
	IDip ≥ (IO +	VO	toff)
	IDip ≥ (IO +	2L	toff)
		2L

≥3.24 A

	CH2
	IDip ≥ (IO +	VO	toff)
	IDip ≥ (IO +	2L	toff)
		2L

≥3.18 A

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Image 29

Contents Package FeaturesDescription PIN Assignments MB39A104PIN Description Pin No Symbol DescriptionsBlock Diagram Parameter Symbol Condition Value Unit Min Typ Parameter Symbol Condition Rating Unit Min MaxAbsolute Maximum Ratings Recommended Operating ConditionsParameter Electrical CharacteristicsPin No Conditions Min Typ MaxPin No Conditions Value Unit Min Parameter SymbolReference Voltage vs. Ambient Temperature Typical CharacteristicsTriangular Wave Oscillation Frequency Power Dissipation vs. Ambient Temperature Functions Under voltage lockout protection circuit Uvlo Timer-latch overcurrent protection circuit block OCPProtection circuit operating function table Operating circuitSetting the Triangular Oscillation Frequency Setting the Output VoltageSetting the SOFT-START and Discharge Times MB39A104 Without Setting Soft-Start Time Treatment Without Using CS TerminalOvercurrent detection circuit About TIMER-LATCH Protection CircuitMethod to detect by mean current Overcurrent Protection Circuit Range of OperationTimer-latch short-circuit protection circuit Resetting the Latch of Each Protection Circuit Treatment Without Using Cscp TerminalEquivalent Circuit On Power on OFF Standby mode Component Specification Vendor Parts ListCH1 Selection of ComponentsCH2 = 3 2 ⋅ 0.05 ⋅ 0.174 = 0.078 W Example Peak-to-peak value ΔIL Di ≥ I O ⋅ 1 − ESR ≤ ΠfC L 050 491 ESR ≤ ΠfC L 033 364 Total Efficiency vs. Input Voltage Reference DataSwitching Wave Form CH1 Ordering Information Usage PrecautionDo not apply negative voltages Part number Package RemarksIndex Package DimensionsFujitsu Limited