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9/94

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 R

O

 Error Amp

Current Mode PWM Controller

The UC1842A/3A/4A/5A family of control ICs is a pin for pin compat-

ible improved version of the UC3842/3/4/5 family. Providing the nec-

essary features to control current mode switched mode power

supplies, this family has the following improved features. Start up cur-

rent 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 V

CC

 over 5V.

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

below.

UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A

BLOCK DIAGRAM

FEATURES

DESCRIPTION

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%

Note 1:          A = DIL-8 Pin Number. B = SO-14 Pin Number.

Note 2: Toggle flip flop used only in 1844A and 1845A.

 A/B

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PACKAGE PIN FUNCTION

FUNCTION

PIN

N/C

1

Comp

2

N/C

3-4

V

FB

5

N/C

6

I

SENSE

7

N/C

8-9

R

T

/C

T

10

N/C

11

Pwr Gnd

12

Gnd

13

N/C

14

Output

15

N/C

16

V

C

17

V

CC

18

N/C

19

V

REF

20

DIL-8, SOIC-8 (TOP VIEW)

J or N, D8 Package

CONNECTION DIAGRAMS

ELECTRICAL CHARACTERISTICS

 Unless otherwise stated, these specifications apply for -55

°

 T

A

 ≤

 125

°

C for the

UC184xA; -40

°

C

 ≤

 T

 85

°

C for the UC284xA; 0

 ≤

 T

 70

°

C for the UC384xA; V

CC

 = 15V (Note 5); R

T

 = 10k; C

T

 = 3.3nF; T

= T

J

; Pin

numbers refer to DIL-8.

PARAMETER

TEST CONDITIONS

UC184xA\UC284xA

UC384xA

UNITS

MIN.

TYP.

MAX.

MIN.

TYP.

MAX. 

Reference Section

Output Voltage

T

= 25°C, I

O

 = 1mA

4.95

5.00

5.05

4.90

5.00

5.10

V

Line Regulation

12 

≤≤

 V

IN

 

≤≤

 25V

6

20

20

mV

Load Regulation

≤≤

 I

O

 

≤≤

 20mA

6

25

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

T

J

 = 25°C (Note 2) 

50

50

µ

V

Long Term Stability

T

A

 = 125°C, 1000Hrs. (Note 2)

 

5

25

5

25

mV

Output Short Circuit

-30

-100

-180

-30

-100

-180

mA

Oscillator Section

Initial Accuracy

T

J

 = 25°C (Note 6)

47

52

57

47

52 

57

kHz

Voltage Stability

12 

≤≤

 V

CC

 

≤≤

 25V

0.2

1

0.2

1

%

Temp. Stability

T

MIN 

≤≤

 

T

A

 

≤≤

 T

MAX 

(Note 2)

5

5

%

Amplitude

V

PIN 4

 peak to peak (Note 2)

1.7

1.7 

V

Discharge Current

T

J

 = 25°C, V

PIN 4 

= 2V (Note 8)

7.8 

8.3

8.8

7.8

8.3

8.8

mA

V

PIN 4

 = 2V (Note 8)

7.5

8.8

7.6

8.8

mA

ABSOLUTE MAXIMUM RATINGS (Note 1)

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 con-

siderations of packages. Pin numbers refer to DIL  package only.

PLCC-20, LCC-20

(TOP VIEW)

Q, L Packages

UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A

Supply Voltage (Low Impedance Source) . . . . . . . . . . . . . . 30V

Supply Voltage (I

CC

 mA). . . . . . . . . . . . . . . . . . . . .  Self Limiting

Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

±

1A

Output Energy (Capacitive Load) . . . . . . . . . . . . . . . . . . . . .  5

µ

J

Analog Inputs (Pins 2, 3) . . . . . . . . . . . . . . . . . .  -0.3V to +6.3V

Error Amp Output Sink Current . . . . . . . . . . . . . . . . . . . .  10mA

Power Dissipation at T

A

 

 25°C (DIL-8) . . . . . . . . . . . . . . . .  1W

Storage Temperature Range . . . . . . . . . . . . .  -65°C to +150°C

Lead Temperature (Soldering, 10 Seconds) . . . . . . . . . .  300°C

SOIC-14 (TOP VIEW)

D Package

2

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PARAMETER

TEST CONDITIONS

UC184xA\UC284xA

UC384xA

UNITS

MIN.

TYP.

MAX.

MIN.

TYP.

MAX. 

Error Amp Section

Input Voltage

V

PIN 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

µ

A

A

VOL

 V

O

 

 4V

65

90

65

90

dB

Unity Gain Bandwidth

T

J

 = 25°C (Note 2) 

0.7

1

0.7

1

MHz

PSRR

12 

 V

CC

 

 

25V

60

70

60

70

dB

Output Sink Current

V

PIN 2

 = 2.7V, V

PIN 1

 = 1.1V

2

6

2

mA

Output Source Current

V

PIN 2

 = 2.3V, V

PIN 1

 = 5V

-0.5

-0.8

 

-0.5

-0.8

mA

V

OUT

 High

V

PIN 2

 = 2.3V, R

L

 = 15k to ground

5

6

5

6

V

V

OUT

 Low

V

PIN 2

 = 2.7V, R

L

 = 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

V

PIN 1

 = 5V (Note 3)

0.9

1

1.1

0.9

1

1.1

V

PSRR

12 

 V

CC

 

 25V (Note 3)

70

70

dB

Input Bias Current

-2

-10

-2

-10

µ

A

Delay to Output

V

PIN 3

 = 0 to 2V (Note 2) 

150

300

150 

300

ns

Output Section

Output Low Level

I

SINK

 = 20mA

0.1

0.4

0.1

0.4

V

I

SINK

 = 200mA

15

2.2

15

2.2

V

Output High Level

I

SOURCE

 = 20mA

13

13.5

13

13.5

V

I

SOURCE

 = 200mA

12

13.5

12

13.5

V

Rise Time

T

J

 = 25°C, C

L

 = 1nF (Note 2)

50

150

50

150 

ns

Fall Time

T

J

 = 25°C, C

L

 = 1nF (Note 2)

50

150

50

150 

ns

UVLO Saturation

V

CC

 = 5V, I

SINK

 = 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

Turn On

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

V

PIN 2

 = V

PIN 3

 = 0V

11

17

11 

17

mA

V

CC

 Zener Voltage

I

CC

 = 25mA

30

34

30

34

V

UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A

Note 2: These parameters, although guaranteed, are not 100%

             tested in production.

Note 3: Parameter measured at trip point of latch with V

PIN2

 = 0.

Note 4: Gain defined as: A 

=

 

V

PIN 1

V

PIN 3

 ; 0 

 V

PIN 3

 

 0.8V.

Note 5: Adjust V

CC

 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 

=

 

V

REF

 

(

max

)

 

 

V

REF

 

(

min

)

T

J

 

(

max

)

 

 

T

J

 

(

min

)

.

             V

REF

 (max) and V

REF

 (min) are the maximum & mini-

             mum reference voltage measured over the appropriate

             temperature range. Note that the extremes in voltage

             do not necessarily occur at the extremes in tempera-

             ture."

Note 8: This parameter is measured with R

T

 = 10k

 to V

REF

.

            This contributes approximately 300

µ

A of current to the

            measurement. The total current flowing into the R

T

/C

T

             

  pin will be approximately 300

µ

A higher than the meas-

 ured value.

ELECTRICAL CHARACTERISTICS (cont.)

 Unless otherwise stated, these specifications apply for -55

°

 T

A

 ≤

 125

°

C for

the UC184xA; -40

°

C

 ≤

 T

 85

°

C for the UC284xA; 0

 ≤

 T

 70

°

C for the UC384xA; V

CC

 = 15V (Note 5); R

T

 = 10k; C

T

 = 3.3nF; T

= T

J

;

Pin numbers refer to DIL-8.

3

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Error Amp Configuration

UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A

Under-Voltage Lockout

During UVLO, the Output is low.

Current Sense Circuit

A small RC filter may be required to suppress switch transients.

Peak Current (I

S

) is Determined By The Formula

I

SMAX

 

 

1.0V

R

S

Error Amp can Source and Sink up to 0.5mA, and Sink up to 2mA.

4

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APPLICATIONS DATA (cont.)

Open-Loop Laboratory Test Fixture

UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A

Output Saturation Characteristics

Error Amplifier Open-Loop Frequency Response

Oscillator Section

Oscillator Frequency vs Timing Resistance

Maximum Duty Cycle vs Timing Resistor

High peak currents associated with capacitive loads necessi-

tate careful grounding techniques. Timing and bypass capaci-

tors should be connected close to pin 5 in a single point

ground. The transistor and 5k potentiometer are used to sam-

ple the oscillator waveform and apply an adjustable ramp to

pin 3.

5

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Off-line Flyback Regulator

Slope Compensation

APPLICATIONS DATA (cont.)

UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A

Power Supply Specifications

1. Input Voltage

95VAC to 130VA

(50 Hz/60Hz)

2. Line Isolation

3750V

3. Switching Frequency

40kHz

4. Efficiency @ Full Load

70%

5. Output Voltage:

A. +5V, 

±

5%; 1A to 4A load

  Ripple voltage: 50mV P-P Max

B. +12V, 

±

3%; 0.1A to 0.3A load

  Ripple voltage: 100mV P-P Max

C. -12V ,

±

3%; 0.1A to 0.3A load

  Ripple voltage: 100mV P-P Max

A fraction of the oscillator ramp can be resistively

summed with the current sense signal to provide slope

compensation for converters requiring duty cycles over

50%.

Note that capacitor, C, forms a filter with R2 to suppress

the leading edge switch spikes.

UNITRODE INTEGRATED CIRCUITS

7 CONTINENTAL BLVD. 

 MERRIMACK, NH  03054

TEL. (603) 424-2410 

 FAX (603)424-3460

6

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any product or service without notice, and advise customers to obtain the latest version of relevant information

to verify, before placing orders, that information being relied on is current and complete. All products are sold

subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those

pertaining to warranty, patent infringement, and limitation of liability.

TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in

accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent

TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily

performed, except those mandated by government requirements.

CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF

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In order to minimize risks associated with the customer’s applications, adequate design and operating

safeguards must be provided by the customer to minimize inherent or procedural hazards.

TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent

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Copyright 

©

 1999, Texas Instruments Incorporated