Texas Instruments UC3851N, UC3851DWTR, UC3851DW, UC2851N, UC2851DWTR Datasheet

UC1851

UC2851

UC3851

Programmable, Off-Line, PWM Controller

FEATURES

∙All Control, Driving, Monitoring, and Protection Functions Included

∙Low-Current Off Line Start Circuit

∙Voltage Feed Forward or Current Mode Control

∙High Current Totem Pole Output

∙50% Absolute Max Duty Cycle

∙PWM Latch for Single Pulse Per Period

∙Pulse-by-Pulse Current Limiting plus Shutdown for Over-Current Fault

∙No Start-Up or Shutdown Transients

∙Slow Turn-On Both Initially and After Fault Shutdown

∙Shutdown Upon Over or Under Voltage Sensing

∙Latch Off or Continuous Retry After Fault

∙1% Reference Accuracy

∙500kHz Operation

∙18 Pin DIL or 20 Pin PLCC Package

DESCRIPTION

The UC1851 family of PWM controllers are optimized for offline primary side control. These devices include a high current totem pole output stage and a toggle flip-flop for absolute 50% duty cycle limiting. In all other respects this line of controllers is pin for pin compatible with the UC1841 series. Inclusion of all major housekeeping functions in these high performance controllers makes them ideal for use in cost sensitive applications.

Important features of these controllers include low current start-up, linear feed-forward for constant volt-second operation, and compatibility with both voltage or current mode control. In addition, these devices include a programmable start threshold, as well as programmable over-voltage, under-voltage, and over current fault thresholds. The fault latch on these devices can be configured for automatic restart, or latched off response to a fault.

These devices are packaged in 18-pin plastic or ceramic dual- in-line packages, or for surface mount applications, a 20 Pin PLCC. The UC1851 is characterized for -55°C to +125°C operation while the UC2851 and UC3851 are designed for -40°C to +85°C and 0°C to +70°C, respectively.

BLOCK DIAGRAM

10/94

ABSOLUTE MAXIMUM RATINGS (Note 1)

Supply Voltage, +VIN (Pin 15)

Voltage Driven . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +32V Current Driven, 100mA maximum. . . . . . . . . . . Self-limiting PWM Output Voltage (Pin 12) . . . . . . . . . . . . . . . . . . . . . . . 40V PWM Output Current, Steady-State (Pin 12) . . . . . . . . . 400mA PWM Output Peak Energy Discharge . . . . . . . . . . . . 20μJoules Driver Bias Current (Pin 14) . . . . . . . . . . . . . . . . . . . . . -200mA Reference Output Current (Pin 16) . . . . . . . . . . . . . . . . -50mA Slow-Start Sink Current (Pin 8) . . . . . . . . . . . . . . . . . . . . 20mA VIN Sense Current (Pin 11). . . . . . . . . . . . . . . . . . . . . . . . 10mA Current Limit Inputs (Pins 6 & 7) . . . . . . . . . . . . . -0.5 to +5.5V Stop Input (Pin 4) . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +5.5V

UC1851

UC2851

UC3851

Comparator Inputs

(Pins 1–7, 9–11, 16). . . . . . . . . . . . . . Internally clamped at 12V Power Dissipation at TA = 25°C (Note 3). . . . . . . . . . . 1000mW Power Dissipation at TC = 25°C (Note 3). . . . . . . . . . . 2000mW Operating Junction Temperature . . . . . . . . . . . -55°C to +150°C Storage Temperature Range . . . . . . . . . . . . . . -65°C to +150°C Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . +300°C

Note 1:All voltages are with respect to ground, Pin 13. Currents are positive-into, negative-out of the specified terminal

Note 2:All pin numbers are referenced to DIL-18 package. Note 3:Consult Packaging Section of Databook for thermal

limitations and considerations of package.

CONNECTION DIAGRAMS

DIL-18, SOIC-18 (TOP VIEW)

J or N, DW Package

PLCC-20, LCC-20	PACKAGE PIN FUNCTIONS
(TOP VIEW)	FUNCTION	PIN
Q, L PACKAGE	COMP	1
	START/UV	2
	OV SENSE	3
	STOP	4
	RESET	5
	CUR THRESH	7
	CUR SENSE	8
	SLOW START	9
	RT/CT	10
	RAMP	11
	VIN SENSE	12
	PWM OUT	13
	GROUND	14
	DRIVE BIAS	15
	+VIN SUPPLY	17
	5.0V REF	18
	INV. INPUT	19
	N.I. INPUT	20

ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for TA = -55°C to +125°C for the UC1851, -40°C to +85°C for the UC2851, and 0°C to 70°C for the UC3851; V IN =

20V, RT = 20kΩ, CT = .001 mfd, RR = 10kΩ, CR = .001mfd. Current Limit Threshold = 200mV, TA = TJ.

PARAMETER	TEST CONDITIONS	UC1851 / UC2851				UC3851			UNITS
		MIN	TYP	MAX	MIN	TYP		MAX
Power Inputs
Start-Up Current	VIN = 30V, Pin 2 = 2.5V		4.5	6		4.5		6	mA
Operating Current	VIN = 30V, Pin 2 = 3.5V		15	21		15		21	mA
Supply OV Clamp	VIN = 20mA	33	39	45	33	39		45	V
Reference Section
Reference Voltage	TJ = 25°C	4.95	5.0	5.05	4.9	5.0		5.1	V
Line Regulation	VIN = 8 to 30V		10	15		10		20	mV
Load Regulation	IL = 0 to 10mA		10	20		10		30	mV
Total Ref Variation	Over Operating Temperature Range	4.9		5.1	4.85			5.15	V
Short Circuit Current	VREF = 0, TJ = 25°C		-80	-100		-80		-100	mA
Oscillator
Nominal Frequency	TJ = 25°C	47	50	53	45	50		55	kHz
Voltage Stability	VIN = 8 to 30V		0.5	1		0.5		1	%
Total Ref Variation	Over Operating Temperature Range	45		55	43			57	kHz
Maximum Frequency	RT = 2kΩ, CT = 330pF	500			500				kHz

2

UC1851

UC2851

UC3851

ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for TA = -55°C to +125°C for the UC1851, -40°C to +85°C for the UC2851, and 0°C to 70°C for the UC3851; V IN =

20V, RT = 20kΩ, CT = .001 mfd, RR = 10kΩ, CR = .001mfd. Current Limit Threshold = 200mV, TA = TJ.

PARAMETER	TEST CONDITIONS	UC1851 / UC2851				UC3851			UNITS
		MIN	TYP	MAX	MIN	TYP		MAX
Ramp Generator
Ramp Current, Minimum	ISENSE = −10μA		-11	-14		-11		-14	μA
Ramp Current, Maximum	ISENSE = 1.0mA	-0.9	-.95		-0.9	-.95			mA
Ramp Valley		0.3	0.4	0.6	0.3	0.4		0.6	V
Ramp Peak	Clamping Level	3.9	4.2	4.5	3.9	4.2		4.5	V
Error Amplifier
Input Offset Voltage	VCM = 5.0V		0.5	5		2		10	mV
Input Bias Current			0.5	2		1		5	μA
Input Offset Current				0.5				0.5	μA
Open Loop Gain	VO = 1 to 3V	60	66		60	66			dB
Output Swing (Max Output ≤	Minimum Total Range	0.3		3.5	0.3			3.5	V
Ramp Peak - 100mV)
CMRR	VCM = 1.5 to 5.5V	70	80		70	80			dB
PSRR	VIN = 8 to 30V	70	80		70	80			dB
Short Circuit Current	VCOMP = 0V		-4	-10		-4		-10	mA
Gain Bandwidth (Note 1)	TJ = 25°C, AVOL = 0dB	1	2		1	2			MHz
Slew Rate (Note 1)	TJ = 25°C, AVCL = 0dB		0.8			0.8			V/μs
PWM Section
Continuous Duty Cycle Range	Minimum Total Continuous Range	2		46	2			46	%
(other than zero) (Note 1)	Ramp Peak < 4.2V
Output High Level	ISOURCE = 20mA	18	18.5		18	18.5			V
	ISOURCE = 200mA	17	18.5		17	18.5			V
Rise Time (Note 1)	TJ = 25°C, CL = 1nF		50	150		50		150	ns
Fall Time (Note 1)	TJ = 25°C, CL = 1nF		50	150		50		150	ns
Output Saturation	IOUT = 20mA		0.2	0.4		0.2		0.4	V
	IOUT = 200mA		1.7	2.2		1.7		2.2	V
Comparator Delay (Note 1)	Pin 8 to Pin 12, TJ = 25°C, R L = 1kΩ		300	500		300		500	ns
Sequencing Functions
Comparator Thresholds	Pins 2, 3, 5	2.8	3.0	3.2	2.8	3.0		3.2	V
Input Bias Current	Pins 3, 5 = 0V		-1.0	-4.0		-1.0		-4.0	μA
Input Leakage	Pins 3, 5 = 10V		0.1	2.0		0.1		2.0	μA
Start/UV Hysteresis Current	Pin 2 = 2.5V	170	200	220	170	200		230	μA
Ext. Stop Threshold	Pin 4	0.8	1.6	2.4	0.8	1.6		2.4	V
Error Latch Activate Current	Pin 4 = 0V, Pin 3 > 3V		-120	-200		-120		-200	μA
Driver Bias Saturation Voltage,	IB = -50mA		2	3		2		3	V
VIN-VOH
Driver Bias Leakage	VB = 0V		-0.1	-10		-0.1		-10	μA
Slow-Start Saturation	IS = 10mA		0.2	0.5		0.2		0.5	V
Slow-Start Leakage	VS = 4.5V		0.1	2.0		0.1		2.0	μA
Current Control
Current Limit Offset			0	5		0		10	mV
Current Shutdown Offset		370	400	430	360	400		440	mV
Input Bias Current	Pin 7 = 0V		-2	-5		-2		-5	μA
Common Mode Range (Note 1)		-0.4		3.0	-0.4			3.0	V
Current Limit Delay (Note 1)	TJ = 25°C, Pin 7 to 12, RL = 1k		200	400		200		400	ns

Note 1:Guaranteed by design. Not 100% tested in production.

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