Method to detect by mean current | Fujitsu MB39A104 specs

MB39A104

Overcurrent Protection Circuit: Range of Operation

When an overcurrent flow occurs, if the increased voltage between the drain and source of the FET is detected by means of the external FET (Q1) resistor, operational stability is lost when the external FET (Q1) ON interval determined by the oscillation frequency, input voltage, and output voltage falls below 450 ns.

Therefore, the circuit should be used within a range that ensures that the ON interval does not fall below 450ns, according to the following formula.

ON interval 450 (ns) ≥	VO (V)
	VIN (V)	⋅
		fOSC (Hz)

If the ON interval of the external FET (Q1) is below 450ns, we recommend the use of an overcurrent detection resistor RS to detect overcurrent, as shown below.

This example shows the range of operation of the overcurrent detection function with a setting of Vo = 3.3V.

• Method to detect by current when external FET(Q1) is turned on
		VIN		Overcurrent Detection Function Operating Range
		VIN	(Rs)
			(Rs)		1600
			ErrAmp		1600
			ErrAmp
			Q1		1400
					1400				VO = set to 3.3 V
	21 (VS2)								VO = set to 3.3 V
	21 (VS2)				1200
	4	VS1		(kHz)	1000
					1000

				fOSC	800
				fOSC
	(ILIM2)				400		Operation Range
−	(ILIM2)
−	20	ILIM1	Connect to RS		200
+	5		when
	5
					0
			using RS		0
			using RS		6	8	10	12	14	16	18	20
								VCC (V)

• Method to detect by mean current
	VIN		Overcurrent Detection Function Operating Range
	VIN
		ErrAmp		1600
	Q1	RS		1400
				1400
	21 (VS2)			1200			VO = set to 3.3 V
	21 (VS2)			1200
	4 VS1		(kHz)	1000
				1000
				800
			fOSC	800
			fOSC	600		Operation Range
				600		Operation Range
−	(ILIM2)			400
−	20 ILIM1			200
+	20 ILIM1
	5


				0	8	10	12	14	16	18	20
				6	8	10	12	14	16	18	20
							VCC (V)

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Image 18

Fujitsu MB39A104 manual Overcurrent Protection Circuit Range of Operation, Method to detect by mean current

Contents

Features DescriptionPackage MB39A104 PIN Assignments Pin No Symbol Descriptions PIN Description Block Diagram Absolute Maximum Ratings Parameter Symbol Condition Rating Unit Min MaxParameter Symbol Condition Value Unit Min Typ Recommended Operating Conditions Pin No Conditions Electrical CharacteristicsParameter Min Typ Max Parameter Symbol Pin No Conditions Value Unit Min Typical Characteristics Reference Voltage vs. Ambient Temperature Triangular Wave Oscillation Frequency Power Dissipation vs. Ambient Temperature Functions Protection circuit operating function table Timer-latch overcurrent protection circuit block OCPUnder voltage lockout protection circuit Uvlo Operating circuit Setting the Output Voltage Setting the Triangular Oscillation Frequency Setting the SOFT-START and Discharge Times MB39A104 Treatment Without Using CS Terminal Without Setting Soft-Start Time About TIMER-LATCH Protection Circuit Overcurrent detection circuit Overcurrent Protection Circuit Range of Operation Method to detect by mean current Timer-latch short-circuit protection circuit Treatment Without Using Cscp Terminal Resetting the Latch of Each Protection Circuit Equivalent Circuit On Power on OFF Standby mode Parts List Component Specification Vendor Selection of Components CH1 CH2 = 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 Reference Data Total Efficiency vs. Input Voltage Switching Wave Form CH1 Do not apply negative voltages Usage PrecautionOrdering Information Part number Package Remarks Package Dimensions Index Fujitsu Limited