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 Fau lt

• No Start-Up or Shutdown Transients

• Slow Turn-On Both Initially and After Fau lt

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

DESCRIPTI ON

The UC1851 fami ly of PWM controllers are optimized for off­line primary side control. These devices include a hi gh 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 compatibl e with the UC1841 series. Inclusion of all
major housekee ping 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 vol tage or curre nt mode control. In
addition, these devices include a programmable start thresh­old, as well as programmable over-voltage, under-voltage, and
over current fault threshol ds. 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 dual­in-line packages, or for surface mount applications, a 20 Pin
PLCC. The UC1851 is characterized for -55°C to +125°C op-
eration while the UC28 51 and UC3851 are designed for -40°C
to +85°C and 0°C to +70°C, respectively.

BLOCK DIAGRAM

10/94

UC1851
UC2851
UC3851

Supply Voltage, +V IN (Pin 15)

Voltage Driven. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +32V

Current Driven, 100 mA m aximum. . . . . . . . . . . Self-limiting

PWM Output Volta ge (Pin 12 ) . . . . . . . . . . . . . . . . . . . . . . . 40V

PWM Out put Current, Ste ady-State (Pin 12). . . . . . . . . 400mA

PWM Output Peak Energy Disc harge . . . . . . . . . . . . 20 µJo ules

Driver Bias Current (Pin 14). . . . . . . . . . . . . . . . . . . . . -200mA

Reference Output Current (Pin 16) . . . . . . . . . . . . . . . . -50mA

Slow-Start Sink Curren t (Pin 8) . . . . . . . . . . . . . . . . . . . . 20mA

V

IN Sense Current (Pin 11). . . . . . . . . . . . . . . . . . . . . . . . 10mA

Current Limit Input s (Pins 6 & 7) . . . . . . . . . . . . . -0.5 to +5. 5V

Stop Input (Pin 4) . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +5.5V

Compara to r Inputs

(Pins 1–7, 9–11, 16). . . . . . . . . . . . . . Internal ly clamp ed at 12V

Power Dissipation at T

A

= 25°C (Note 3). . . . . . . . . . . 1000mW

Power Dissipation at T

C

= 25°C (Note 3). . . . . . . . . . . 2000mW

Operating Junct ion Te mp era tu re. . . . . . . . . . . -55°C to +150°C

Storage Temperature Ra nge. . . . . . . . . . . . . . -65°C to +150°C

Lead Temp era ture (Solder ing, 10 sec) . . . . . . . . . . . . . +300°C

Note 1:All voltages are with res pect to gro und, Pin 13.
Currents are positive-into, negative-out of the

specified terminal
Note 2:All pin number s are refer enc ed t o DIL-18 packa ge.
Note 3:Co nsult Packaging Sect ion of Dat abo ok for ther m al

limitations and cons id era tion s of packa ge.

DIL-18, SOIC- 18 (T O P VIEW)
J or N, DW Package

CONNECTION DIAGRAMS

PACKAGE PIN FUNCTIONS

FUNCTION PIN

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

PLCC-20, LCC-20
(TOP VIEW)
Q, L PACKAGE

ABSOLUTE MAXI MUM RATING S (Note 1)

Unless otherw ise stat ed, these sp ecif icat io ns 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, R

T = 20kΩ, C T = .001 m fd , RR = 10kΩ, CR = .001mfd. Current Limit Threshold

= 200mV, T

A = TJ.

ELECTRICAL CHARACTERISTICS:

PARAMETER TEST CONDITIONS

UC1851 / UC2851 UC3851 UNITS

MIN TYP MAX MIN TYP MAX

Power Inputs

Start-Up Curr ent V

IN = 30V, Pin 2 = 2.5V 4.5 6 4.5 6 mA

Operating Cur ren t V

IN = 30V, Pin 2 = 3.5V 15 21 15 21 mA

Supply OV Clamp V

IN

= 20mA 333945333945V

Reference Sec tio n

Reference Voltage T

J = 25°C 4.95 5.0 5.05 4.9 5.0 5.1 V

Line Regulation V

IN

= 8 to 30V 10 15 10 20 mV

Load Regulation I

L = 0 to 10mA 1020 1030mV

Total Ref Variatio n Over Operating Temper at ure Range 4.9 5.1 4.85 5.15 V
Short Circuit Current V

REF = 0, TJ = 25°C -80 -100 -80 -100 mA

Oscillator

Nominal Frequency T

J = 25°C 47 50 53 45 50 55 kHz

Voltage Stability VIN = 8 to 30V 0.5 1 0.5 1 %
Total Ref Variatio n Over Operating Temper at ure Range 45 55 43 57 kH z
Maximum Frequency

R

T = 2kΩ, CT = 330pF

500 500 kHz

2

ELECTRICAL CHARACTERISTICS:

PARAMETER TEST CONDITIONS UC1851 / UC2851 UC3851 UNITS

MIN TYP MAX MIN TYP MAX

Ramp Ge nerator

Ramp Curren t, M in imum

I

SENSE = −10µA

-11 -14 -11 -14 µA

Ramp Current, Maximum I

SENSE = 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 Offs et Vo lta g e V

CM = 5.0V 0.5 5 2 10 m V

Input Bias Cur ren t 0.5 2 1 5 µA
Input Offs et Cu rr ent 0.5 0.5 µA
Open Loop Gain

∆V

O = 1 to 3V

60 66 60 66 dB

Output Swing (Max Ou tp ut ≤
Ramp Peak - 100mV)

Minimum Total Range 0.3 3.5 0.3 3.5 V

CMRR V

CM = 1.5 to 5.5V 70 80 70 80 dB

PSRR V

IN = 8 to 30V 70 80 70 80 dB

Short Circuit Current V

COMP = 0V -4 -10 -4 -10 mA

Gain Bandwidth (Not e 1) T

J = 25°C, AVOL = 0dB 1 2 1 2 MHz

Slew Rate (Note 1) T

J = 25°C, AVCL = 0dB 0.8 0.8 V/µs

PWM Section

Continuous Duty Cycle Range
(other than zero) (Note 1)

Minimum Total Cont inuou s Range
Ramp Peak < 4.2V

246246%

Output High Leve l I

SOURCE = 20mA 18 18.5 18 18. 5 V

I

SOURCE = 200mA 17 18.5 17 18.5 V

Rise Time (Note 1) T

J = 25°C, CL = 1nF 50 150 50 150 ns

Fall Time (Note 1) T

J = 25°C, CL = 1nF 50 150 50 150 ns

Output Saturation I

OUT = 20mA 0.2 0.4 0.2 0.4 V

I

OUT = 200mA 1.7 2.2 1.7 2.2 V

Comparator Delay (Note 1)

Pin 8 to Pin 12, T

J = 25°C, RL = 1kΩ

300 500 300 500 ns

Sequencing Functions

Comparator Thre sholds P ins 2, 3, 5 2.8 3.0 3.2 2.8 3.0 3.2 V
Input Bias Curren t 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 Hyster esis Cur ren t Pin 2 = 2.5V 170 200 220 17 0 200 2 30 µA
Ext. Stop Threshold Pin 4 0.8 1.6 2.4 0.8 1.6 2.4 V
Error Latch Activat e Cur ren t Pin 4 = 0V, Pin 3 > 3V -120 -200 -120 -200 µA
Driver Bias Saturation Volta ge,

V

IN-VOH

IB = -50mA 2 3 2 3 V

Driver Bias Leakage V

B = 0V -0.1 -10 -0.1 -10 µA

Slow-Start Saturation I

S = 10mA 0.2 0.5 0.2 0.5 V

Slow-Start Leakage V

S = 4.5V 0.1 2.0 0.1 2.0 µA

Current Control

Current Limit Off set 0 5 0 10 mV
Current Shutdown O ffs et 370 400 430 360 400 440 mV
Input Bias Current Pin 7 = 0V -2 -5 -2 -5 µA
Common Mode Ran ge (No te 1) -0.4 3.0 -0.4 3.0 V
Current Limit Delay (Note 1) T

J = 25°C, Pin 7 to 12, RL = 1k 200 400 200 400 ns

Note 1:Guaranteed by d esign. Not 100% test ed in production.

UC1851
UC2851
UC3851

Unless otherw ise stat ed, these sp ecif icat io ns 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; VIN =
20V, RT = 20 kΩ, CT = .0 01 mfd , R R = 10kΩ, CR = .001mfd. Current Limit Threshold
= 200mV, T A = TJ.

3