UC3843DX Datasheet UC3842N, UC3843DX, UC3844DX | P1-P3

www.fairchildsemi.com

Rev. 1.0.1

Features

• Low Start up Current

• Maximum Duty Clamp

• UVLO With Hysteresis

• Operating Frequency up to 500KHz

Description

The UC3842/UC3843/UC3844/UC3845 are fixed

frequencycurrent-mode PWM controller. They are specially

designed for Off-Line and DC to DC converter applications

with minimum external components. These integrated

circuits feature a trimmed oscillator for precise duty cycle

control, a temperature compensated reference, high gain

error amplifier, current sensing comparator and a high

current totempole output for driving a Power MOSFET. The

UC3842 and UC3844 have UVLO thresholds of 16V (on)

and 10V (off). The UC3843 and UC3845 are 8.5V(on) and

7.9V (off). The UC3842 and UC3843 can operate within

100% duty cycle. The UC3844 and UC3845 can operate

with 50% duty cycle.

8-DIP

14-SOP

1

8-SOP

1

Internal Block Diagram

UC3842/UC3843/UC3844/UC3845

SMPS Controller

* NORMALLY 8DIP/8SOP PIN NO.

* ( ) IS 14SOP PINNO.

* TOGGLE FLIP FLOP USED ONLY IN UC3844, UC3845

UC3842/UC3843/UC3844/UC3845

2

Absolute Maximum Ratings

Note:

1. Board Thickness 1.6mm, Board Dimension 76.2mm ×114.3mm, (Reference EIA / JSED51-3, 51-7)

2. Do not exceeed P

D

and SOA (Safe Operation Area)

Power Dissipation Curve

Thermal Data

Pin Array

Parameter Symbol Value Unit

Supply Voltage V

CC

30 V

Output Current I

O

±1A

Analog Inputs (Pin 2.3) V

(ANA)

-0.3 to 6.3 V

Error Amp Output Sink Current I

SINK (E.A)

10 mA

Power Dissipation at T

A

≤25°C (8DIP) P

D

(Note1,2) 1200 mW

Power Dissipation at T

A

≤25°C (8SOP) P

D

(Note1,2) 460 mW

Power Dissipation at T

A

≤25°C (14SOP) P

D

(Note1,2) 680 mW

Storage Temperature Range T

STG

-65 ~ +150 °C

Lead Temperature (Soldering, 10sec) T

LEAD

+300 °C

Characteristic Symbol 8-DIP 8-SOP 14-SOP Unit

Thermal Resistance Junction-ambient R

thj-amb(MAX)

100 265 180 °C/W

800

700

600

500

400

300

900

1000

1100

0 102030405060708090100110120130140150

AMBIENT TEMPERATURE (℃)

POWER DISSIPATION (mW)

1200

8DIP

14SOP

8SOP

800

700

600

500

400

300

900

1000

1100

0 102030405030 40 50 60 70 8060 70 80 90 100 11090 100 110 120 130 140120 130 140 150

AMBIENT TEMPERATURE (℃)

POWER DISSIPATION (mW)

1200

8DIP

14SOP

8SOP

V

CC

GND

PWR GND

COMP

1

N/C 2

V

FB

N/C

3

4

V

REF

N/C

PWR V

C

14

13

12

11

CURRENT SENSE 5

N/C

R

T/

C

T

6

7

OUTPUT

10

9

8

COMP

1

V

FB

2

CURRENT SENSE

R

T/

C

T

3

4

V

REF

V

CC

OUTPUT

GND

8

7

6

5

8DIP,8SOP

14SOP

V

CC

GND

PWR GND

COMP

1

N/C 2

V

FB

N/C

3

4

V

REF

N/C

PWR V

C

14

13

12

11

CURRENT SENSE 5

N/C

R

T/

C

T

6

7

OUTPUT

10

9

8

V

CC

GND

PWR GND

COMP

1

N/C 2

V

FB

N/C

3

4

V

REF

N/C

PWR V

C

14

13

12

11

CURRENT SENSE 5

N/C

R

T/

C

T

6

7

OUTPUT

10

9

8

COMP

1

V

FB

2

CURRENT SENSE

R

T/

C

T

3

4

V

REF

V

CC

OUTPUT

GND

8

7

6

5

COMP

1

V

FB

2

CURRENT SENSE

R

T/

C

T

3

4

V

REF

V

CC

OUTPUT

GND

8

7

6

5

8DIP,8SOP

14SOP

UC3842/UC3843/UC3844/UC3845

3

Electrical Characteristics

(V

CC

=15V, R

T

=10kΩ, C

T

=3.3nF, T

A

= 0°C to +70°C, unless otherwise specified)

Parameter Symbol Conditions Min. Typ. Max. Unit

REFERENCE SECTION

Reference Output Voltage V

REF

T

J

= 25°C, I

REF

= 1mA 4.90 5.00 5.10 V

Line Regulation ∆V

REF

12V ≤ V

CC

≤ 25V - 6 20 mV

Load Regulation ∆V

REF

1mA ≤ I

REF

≤ 20mA - 6 25 mV

Short Circuit Output Current I

SC

T

A

= 25°C - -100 -180 mA

OSCILLATOR SECTION

Oscillation Frequency f T

J

= 25°C475257kHz

Frequency Change with

Voltage

∆f/∆V

CC

12V ≤ V

CC

≤ 25V - 0.05 1 %

Oscillator Amplitude V

OSC

- -1.6-V

P-P

ERROR AMPLIFIER SECTION

Input Bias Current I

BIAS

- --0.1-2µA

Input Voltage V

I(E>A)

V

pin1

= 2.5V 2.42 2.50 2.58 V

Open Loop Voltage Gain G

VO

2V ≤ V

O

≤ 4V (Note3) 65 90 - dB

Power Supply Rejection Ratio PSRR 12V ≤ V

CC

≤ 25V (Note3) 60 70 - dB

Output Sink Current I

SINK

V

pin2

= 2.7V, V

pin1

= 1.1V 2 7 - mA

Output Source Current I

SOURCE

V

pin2

= 2.3V, V

pin1

= 5V -0.6 -1.0 - mA

High Output Voltage V

OH

V

pin2

= 2.3V, R

L

= 15kΩ to GND 5 6 - V

Low Output Voltage V

OL

V

pin2

= 2.7V, R

L

= 15kΩ to Pin 8 - 0.8 1.1 V

CURRENT SENSE SECTION

Gain G

V

(Note 1 & 2) 2.85 3 3.15 V/V

Maximum Input Signal V

I(MAX)

V

pin1

= 5V(Note 1) 0.9 1 1.1 V

Power Supply Rejection Ratio PSRR 12V ≤ V

CC

≤ 25V (Note 1,3) - 70 - dB

Input Bias Current I

BIAS

- --3-10µA

OUTPUT SECTION

Low Output Voltage

V

OL

I

SINK

= 20mA - 0.08 0.4 V

I

SINK

= 200mA - 1.4 2.2 V

High Output Voltage

V

OH

I

SOURCE

= 20mA 13 13.5 - V

I

SOURCE

= 200mA 12 13.0 - V

Rise Time t

R

T

J

= 25°C, C

L

= 1nF (Note 3) - 45 150 ns

Fall Time t

F

T

J

= 25°C, C

L

= 1nF (Note 3) - 35 150 ns

UNDER-VOLTAGE LOCKOUT SECTION

Start Threshold

V

TH(ST)

UC3842/UC3844 14.5 16.0 17.5 V

UC3843/UC3845 7.8 8.4 9.0 V

Min. Operating Voltage

(After Turn On)

V

OPR(MIN)

UC3842/UC3844 8.5 10.0 11.5 V

UC3843/UC3844 7.0 7.6 8.2 V

UC3843DX

UC3843DX

Products related to this Datasheet