Texas Instruments UC3845AN, UC3845AD8TR, UC3845AD8, UC3845AD, UC3844AD8 Datasheet

UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A

Current Mode PWM Controller

FEATURES

∙Optimized for Off-line and DC to DC Converters

∙Low Start Up Current (<0.5mA)

∙Trimmed Oscillator Discharge Current

∙Automatic Feed Forward Compensation

∙Pulse-by-Pulse Current Limiting

∙Enhanced Load Response Characteristics

∙Under-Voltage Lockout With Hysteresis

∙Double Pulse Suppression

∙High Current Totem Pole Output

∙Internally Trimmed Bandgap Reference

∙500kHz Operation

∙Low RO Error Amp

DESCRIPTION

The UC1842A/3A/4A/5A family of control ICs is a pin for pin compatible improved version of the UC3842/3/4/5 family. Providing the necessary features to control current mode switched mode power supplies, this family has the following improved features. Start up current is guaranteed to be less than 0.5mA. Oscillator discharge is trimmed to 8.3mA. During under voltage lockout, the output stage can sink at least 10mA at less than 1.2V for VCC over 5V.

The difference between members of this family are shown in the table below.

	Part #	UVLO On	UVLO Off	Maximum Duty
				Cycle
	UC1842A	16.0V	10.0V	<100%
	UC1843A	8.5V	7.9V	<100%
	UC1844A	16.0V	10.0V	<50%
	UC1845A	8.5V	7.9V	<50%

BLOCK DIAGRAM

Note 1: A/B A = DIL-8 Pin Number. B = SO-14 Pin Number. Note 2: Toggle flip flop used only in 1844A and 1845A.

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ABSOLUTE MAXIMUM RATINGS (Note 1)

Supply Voltage (Low Impedance Source) . . . . . . . . . . . . . . 30V Supply Voltage (ICC mA). . . . . . . . . . . . . . . . . . . . . Self Limiting Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±1A Output Energy (Capacitive Load) . . . . . . . . . . . . . . . . . . . . . 5μJ Analog Inputs (Pins 2, 3) . . . . . . . . . . . . . . . . . . -0.3V to +6.3V Error Amp Output Sink Current . . . . . . . . . . . . . . . . . . . . 10mA Power Dissipation at TA ≤ 25°C (DIL-8) . . . . . . . . . . . . . . . . 1W Storage Temperature Range . . . . . . . . . . . . . -65°C to +150°C Lead Temperature (Soldering, 10 Seconds) . . . . . . . . . . 300°C

Note 1. All voltages are with respect to Ground, Pin 5. Currents are positive into, negative out of the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages. Pin numbers refer to DIL package only.

SOIC-14 (TOP VIEW)

D Package

UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A

CONNECTION DIAGRAMS

DIL-8, SOIC-8 (TOP VIEW)

J or N, D8 Package

PLCC-20, LCC-20	PACKAGE PIN FUNCTION
(TOP VIEW)	FUNCTION	PIN
Q, L Packages	N/C	1
	Comp	2
	N/C	3-4
	VFB	5
	N/C	6
	ISENSE	7
	N/C	8-9
	RT/CT	10
	N/C	11
	Pwr Gnd	12
	Gnd	13
	N/C	14
	Output	15
	N/C	16
	VC	17
	VCC	18
	N/C	19
	VREF	20

ELECTRICAL CHARACTERISTICS Unless otherwise stated, these specifications apply for -55°C ≤ TA ≤ 125°C for the UC184xA; -40°C ≤ TA ≤ 85°C for the UC284xA; 0 ≤ TA ≤ 70°C for the UC384xA; VCC = 15V (Note 5); RT = 10k; CT = 3.3nF; TA = TJ; Pin numbers refer to DIL-8.

	PARAMETER	TEST CONDITIONS	UC184xA\UC284xA				UC384xA				UNITS
			MIN.	TYP.	MAX.	MIN.		TYP.	MAX.
	Reference Section
	Output Voltage	TJ = 25°C, IO = 1mA	4.95	5.00	5.05	4.90		5.00		5.10	V
	Line Regulation	12 ≤ VIN ≤ 25V		6	20			6		20	mV
	Load Regulation	1 ≤ IO ≤ 20mA		6	25			6		25	mV
	Temp. Stability	(Note 2, Note 7)		0.2	0.4			0.2		0.4	mV/°C
	Total Output Variation	Line, Load, Temp.	4.9		5.1	4.82				5.18	V
	Output Noise Voltage	10Hz ≤ f ≤ 10kHz
		TJ = 25°C (Note 2)		50				50			μV
	Long Term Stability	TA = 125°C, 1000Hrs. (Note 2)		5	25			5		25	mV
	Output Short Circuit		-30	-100	-180	-30		-100		-180	mA
	Oscillator Section
	Initial Accuracy	TJ = 25°C (Note 6)	47	52	57	47		52		57	kHz
	Voltage Stability	12 ≤ VCC ≤ 25V		0.2	1			0.2		1	%
	Temp. Stability	TMIN ≤ TA ≤ TMAX (Note 2)		5				5			%
	Amplitude	VPIN 4 peak to peak (Note 2)		1.7				1.7			V
	Discharge Current	TJ = 25°C, VPIN 4 = 2V (Note 8)	7.8	8.3	8.8	7.8		8.3		8.8	mA
		VPIN 4 = 2V (Note 8)	7.5		8.8	7.6				8.8	mA

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UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A ELECTRICAL CHARACTERISTICS (cont.) Unless otherwise stated, these specifications apply for -55°C ≤ TA ≤ 125°C for the UC184xA; -40°C ≤ TA ≤ 85°C for the UC284xA; 0 ≤ TA ≤ 70°C for the UC384xA; VCC = 15V (Note 5); RT = 10k; CT = 3.3nF; TA = TJ; Pin numbers refer to DIL-8.

	PARAMETER	TEST CONDITIONS	UC184xA\UC284xA				UC384xA				UNITS
			MIN.	TYP.	MAX.	MIN.		TYP.	MAX.
	Error Amp Section
	Input Voltage	VPIN 1 = 2.5V	2.45	2.50	2.55	2.42		2.50		2.58	V
	Input Bias Current			-0.3	-1			-0.3		-2	μA
	AVOL	2 ≤ VO ≤ 4V	65	90		65		90			dB
	Unity Gain Bandwidth	TJ = 25°C (Note 2)	0.7	1		0.7		1			MHz
	PSRR	12 ≤ VCC ≤ 25V	60	70		60		70			dB
	Output Sink Current	VPIN 2 = 2.7V, VPIN 1 = 1.1V	2	6		2		6			mA
	Output Source Current	VPIN 2 = 2.3V, VPIN 1 = 5V	-0.5	-0.8		-0.5		-0.8			mA
	VOUT High	VPIN 2 = 2.3V, RL = 15k to ground	5	6		5		6			V
	VOUT Low	VPIN 2 = 2.7V, RL = 15k to Pin 8		0.7	1.1			0.7		1.1	V
	Current Sense Section
	Gain	(Note 3, Note 4)	2.85	3	3.15	2.85		3		3.15	V/V
	Maximum Input Signal	VPIN 1 = 5V (Note 3)	0.9	1	1.1	0.9		1		1.1	V
	PSRR	12 ≤ VCC ≤ 25V (Note 3)		70				70			dB
	Input Bias Current			-2	-10			-2		-10	μA
	Delay to Output	VPIN 3 = 0 to 2V (Note 2)		150	300			150		300	ns
	Output Section
	Output Low Level	ISINK = 20mA		0.1	0.4			0.1		0.4	V
		ISINK = 200mA		15	2.2			15		2.2	V
	Output High Level	ISOURCE = 20mA	13	13.5		13		13.5			V
		ISOURCE = 200mA	12	13.5		12		13.5			V
	Rise Time	TJ = 25°C, CL = 1nF (Note 2)		50	150			50		150	ns
	Fall Time	TJ = 25°C, CL = 1nF (Note 2)		50	150			50		150	ns
	UVLO Saturation	VCC = 5V, ISINK = 10mA		0.7	1.2			0.7		1.2	V
	Under-Voltage Lockout Section
	Start Threshold	x842A/4A	15	16	17	14.5		16		17.5	V
		x843A/5A	7.8	8.4	9.0	7.8		8.4		9.0	V
	Min. Operation Voltage After	x842A/4A	9	10	11	8.5		10		11.5	V
	TurnOn	x843A/5A	7.0	7.6	8.2	7.0		7.6		8.2	V
	PWM Section
	Maximum Duty Cycle	x842A/3A	94	96	100	94		96		100	%
		x844A/5A	47	48	50	47		48		50	%
	Minimum Duty Cycle				0					0	%
	Total Standby Current
	Start-Up Current			0.3	0.5			0.3		0.5	mA
	Operating Supply Current	VPIN 2 = VPIN 3 = 0V		11	17			11		17	mA
	VCC Zener Voltage	ICC = 25mA	30	34		30		34			V

Note 2: These parameters, although guaranteed, are not 100% tested in production.

Note 3: Parameter measured at trip point of latch with VPIN2 = 0.

Note 4: Gain defined as: A =	VPIN 1	; 0 ≤ VPIN 3 ≤ 0.8V.
	VPIN 3

Note 5: Adjust VCC above the start threshold before setting at 15V.

Note 6: Output frequency equals oscillator frequency for the UC1842A and UC1843A. Output frequency is one half oscillator frequency for the UC1844A and UC1845A.

Note 7: "Temperature stability, sometimes referred to as average temperature coefficient, is described by the equation:

Temp Stability = VREF (max) − VREF (min). TJ (max) − TJ (min)

VREF (max) and VREF (min) are the maximum & minimum reference voltage measured over the appropriate temperature range. Note that the extremes in voltage do not necessarily occur at the extremes in temperature."

Note 8: This parameter is measured with RT = 10kΩ to VREF. This contributes approximately 300μA of current to the measurement. The total current flowing into the RT/CT pin will be approximately 300μA higher than the measured value.

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