KA3844B.pdf

www.fairchildsemi.com

KA3842B/KA3843B/KA3844B/

KA3845B

SMPS Controller

Features

• Low Start up Current

• Maximum Duty Clamp

• UVLO With Hysteresis

• Operating Frequency up to 500KHz

Description

The KA3842B/KA3843B/KA3844B/KA3845B are fixed

frequency current-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 KA3842B and KA3844B have UVLO thresholds of

16V (on) and 10V (off). The KA3843B and KA3845B are

8.5V (on) and 7.9V (off). The KA3842B and KA3843B can

operate within 100% duty cycle. The KA3844B and

KA3845B can operate w ith 50% duty cycle.

8-DIP

14-SOP

Internal Block Diagram

Rev. 1.0.2

KA3842B/KA3843B/KA3844B/KA3845B

Absolute Maximum Ratings

Parameter

Symbol

Value

Unit

Supply Voltage

V CC

Output Current

I O

Analog Inputs (Pin 2.3)

V (ANA)

-0.3 to 6.3

Error Amp Output Sink Current

ISINK (E.A)

Power Dissipation at T A

C (8DIP)

P D (Note1,2)

1200

Power Dissipation at T A

C (14SOP)

P D (Note1,2)

680

Storage Temperature Range

T STG

-65 ~ +150

Lead Temperature (Soldering, 10sec)

T LEAD

+300

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

1200

1100

8DIP

1000

900

800

700

600

500

400

300

14SOP

0 00000

30 40 50 60 70 80

60 70 80 90 100 110

90 100 110 120 130 140

120 130 140 150

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

AMBIENT TEMPERATURE ( ℃ )

Thermal Data

Characteristic

Symbol

8-DIP

14-SOP

Unit

Thermal Resistance Junction-ambient

R thj-amb(MAX)

100

180

C/W

Pin Array

8DIP,8SOP

8-DIP

14SOP

COMP 1

V REF

COMP 1

V REF

V FB 2

V CC

N/C 2

N/C

CURRENT SENSE

OUTPUT

V FB

V CC

R T/ C T

GND

N/C

PWR V C

CURRENT SENSE 5

OUTPUT

N/C

GND

R T/ C T

PWR GND

1200

8DIP

1100

1000

900

800

700

600

500

400

300

14SOP

AMBIENT TEMPERATURE ( ℃ )

8DIP,8SOP

14SOP

V REF

COMP 1

V REF

V FB 2

V CC

N/C 2

N/C

V FB

CURRENT SENSE

OUTPUT

V CC

R T/ C T

GND

N/C

PWR V C

CURRENT SENSE 5

OUTPUT

N/C

GND

R T/ C T

PWR GND

KA3842B/KA3843B/KA3844B/KA3845B

Electrical Characteristics

(V CC =15V, R T =10K

, 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

Line Regulation

V REF

12V

V CC

25V

Load Regulation

V REF

1mA

I REF

20mA

Short Circuit Output Current

I SC

T A = 25

-100 -180 mA

OSCILLATOR SECTION

Oscillation Frequency

T J = 25

57 KHz

Frequency Change with Voltage

V CC

12V

V CC

25V

0.05

Oscillator Amplitude

VOSC

1.6

P-P

ERROR AMPLIFIER SECTION

Input Bias Current

I BIAS

-0.1

-2

Input Voltage

V I(E>A)

V pin1 = 2.5V

2.42 2.50 2.58

Open Loop Voltage Gain

G VO

V O

4V (Note3)

Power Supply Rejection Ratio

PSRR

12V

V CC

25V (Note3)

Output Sink Current

I SINK

V pin2 = 2.7V, V pin1 = 1.1V

Output Source Current

I SOURCE V pin2 = 2.3V, V pin1 = 5V

-0.6 -1.0

High Output Voltage

V OH

V pin2 = 2.3V, R L = 15K

to D5

Low Output Voltage

V OL

V pin2 = 2.7V, R L = 15K

to Pin 8

0.8

1.1

CURRENT SENSE SECTION

Gain

G V

(Note 1 & 2)

2.85

3.15 V/V

Maximum Input Signal

V I(MAX)

V pin1 = 5V(Note 1)

0.9

1.1

Power Supply Rejection Ratio

PSRR

12V

V CC

25V (Note1,3)

Input Bias Current

I BIAS

-3

-10

OUTPUT SECTION

Low Output Voltage

VOL

ISINK = 20mA

0.08 0.4

I SINK = 200mA

1.4

2.2

High Output Voltage

V OH

I SOURCE = 20mA

13.5

I SOURCE = 200mA

13.0

Rise Time

t R

T J = 25

C, C L = 1nF (Note 3)

150

Fall Time

t F

T J = 25

C, C L = 1nF (Note 3)

150

UNDER-VOLTAGE LOCKOUT SECTION

Start Threshold

VTH(ST)

KA3842B/KA3844B

14.5 16.0 17.5

KA3843B/KA3845B

7.8

8.4

9.0

Min. Operating Voltage

(After Turn On)

V OPR(MIN)

KA3842B/KA3844B

8.5 10.0 11.5

KA3843B/KA3845B

7.0

7.6

8.2

KA3842B/KA3843B/KA3844B/KA3845B

Electrical Characteristics (Continued)

(V CC =15V, R T =10K

, C T =3.3nF, T A = 0

C to +70

C unless otherwise specified)

Parameter

Symbol

Conditions

Min.

Typ. Max. Unit

PWM SECTION

Max. Duty Cycle

D (Max)

KA3842B/KA3843B

100

D (MAX)

KA3844B/KA3845B

Min. Duty Cycle

D (MIN)

TOTAL STANDBY CURRENT

Start-Up Current

I ST

0.45

Operating Supply Current

I CC(OPR) V pin3 =V pin2 =ON

Zener Voltage

V Z

I CC = 25mA

Adjust V CC above the start threshould before setting at 15V

Note:

1. Parameter measured at trip point of latch

2. Gain defined as:

V pin1

V pin3

0.8V

V pin3

3. These parameters, although guaranteed, are not 100 tested in production.

Figure 1. Open Loop Test Circuit

High peak currents associated with capacitive loads necessitate careful grounding techniques Timing and bypass capacitors

should be connected close to pin 5 in a single point ground. The transistor and 5K

potentiometer are used to sample the

oscillator waveform and apply an adjustable ramp to pin 3.

------------------

KA3842B/KA3843B/KA3844B/KA3845B

Figure 2. Under Voltage Lockout

During Under-Voltage Lock-Out, the output driver is biased to a high impedance state. Pin 6 should be shunted to ground with

a bleeder resistor to prevent activating the power switch with output leakage current.

Figure 3. Error Amp Configuration

Figure 4. Current Sense Circuit

Peak current (I S ) is determined by the formula:

I S

MAX

1.0V

R S

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

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