UC3842A-D08-T - Unisonic Technologies Co., Ltd.

UNISONIC TECHNOLOGIES CO., LTD

UC3842A/3843A LINEAR INTEGRATED CIRCUIT

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CURRENT MODE PWM

CONTROL CIRCUITS

 DESCRIPTION

The UTC UC3842A/3843A provide the necessary functions to

implement off-line or DC to DC fixed frequency current mode ,

controlled switching circuits with minimal external components.

 FEATURES

*Low Start Up Current ( Typical 0.12mA )

*Automatic Feed Forward Compensation

*Pulse-by-Pulse Current Limiting

*Under-voltage Lockout with Hysteresis

*Double Pulse Suppr ession

*High Current Totem Pole Output to Drive MOSFET Directly

*Internally Trimmed Band Gap Reference

*500kHz Operation

 ORDERING INFORMATION

Ordering Number

Normal Lead Free Plating Halogen Free Package Packing

UC3842A-D08-T UC3842AL-D08-T UC3842AP-D08-T DIP-8 Tube

UC3842A-S08-R UC3842AL-S08-R UC3842AP-S08-R SOP-8 Tape Reel

UC3842A-S08-T UC3842AL-S08-T UC3842AP-S08-T SOP-8 Tube

UC3843A-D08-T UC3843AL-D08-T UC3843AP-D08-T DIP-8 Tube

UC3843A-S08-R UC3843AL-S08-R UC3843AP-S08-R SOP-8 Tape Reel

UC3843A-S08-T UC3843AL-S08-T UC3843AP-S08-T SOP-8 Tube

UC3842A/3843A LINEAR INTEGRATED CIRCUIT

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 PIN CONFIGURATION

RT/CT

Output

GND

1

2

3

4

8

7

5

6

Current Sense

COMP

VFB

VREF

VCC

 BLOCK DIAGRAM

7

5

7

6

5

4

3

1

2

8

Internal

Bias

5V REF S/R

U.V.L.O

R

S

PWM

LATCH

ERROR

AMPLIFIER

1V

OSCILLATOR

VFB

COMP

CURRENT SENSE

RT/CT

Vcc

GND

OUTPUT

Vcc

GND

CURRENT

SENSE

COMPARATOR

VREF

1/2VRE

F

VREF

Good

Logic

1/3VREF

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 ABSOLUTE MAXIMUM RATINGS (Ta=25℃)

PARAMETER SYMBOL RATINGS UNIT

Supply Voltage(Low Impedance Source) VCC 30 V

Supply Voltage(ICC<30mA) VCC Self Limiting V

Output Current ( Peak ) IO(PEAK) ±1 A

Output Energy (capacity Load ) 5 μJ

Analog Inputs(pin 2,3) VI(ANA) -0.3 ~ +6.3 V

Error Amplifier Output Sink Current ISINK(EA) 10 mA

DIP-8 1.0 W

Power Dissipation( Ta≦25°C) SOP-8 PD 0.5 W

Derated at Ta>25°C PD 8 mW/°C

Junction Temperature TJ +150 °C

Storage Temperature TSTG -65 ~ +150 °C

Note Absolute maximum ratings are those values beyond which the device which the device could be permanently

damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied.

 ELECTRICAL CHARACTERISTICS

(0°C≦Ta≦70°C, VCC=15V, RT=10kΩ, CT=3.3nF, unless otherwise specified)

PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT

Reference Section

Output Voltage VREF T

J=25°C,IOUT=1mA 4.9 5 5.1 V

Line Regulation ΔVREF 12≦VIN25V 6 20 mV

Load Regulation ΔVREF 1≦IOUT=20mA 6 25 mV

Temperature Stability (Note 1) 0.2 0.4 mV/°C

Total Output Variation Line, Load, Temp(Note 1) 4.82 5.18 V

Output Noise Voltage Vosc 10Hz≦f≦10kHz,TJ=25°C (Note 1) 50 μV

Long Term Stability Ta=25°C,1000Hrs(Note 1) 5 25 mV

Output Short Circuit ISC -30 -100 -180 mA

Oscillator Section

Initial Accuracy f TJ=25°C 47 52 57 kHz

Voltage Stability Δf/ΔVcc 12≦VCC≦25V 0.2 1 %

Temperature Stability Tmin≦Ta≦Tmax(Note 1) 5 %

Amplitude Vosc Vpin 4 peak to peak 1.7 V

Error Amplifier Section

Input Voltage VI(EA) Vpin 1=2.5V 2.42 2.50 2.58 V

Input Bias Current II(BIAS) -0.3 -2 μA

AVOL

2 ≦VOUT≦4V 60 90 dB

Unity Gain Bandwidth TJ=25°C (Note 1) 0.7 1 MHz

PSRR

I2≦VCC≦25V 60 70 dB

Output Sink Current IO(SINK) Vpin 2=2.7V,Vpin 1=1.1V 2 6 mA

Output Source Current IO(SOURCE) Vpin 2=2.3V,Vpin 1=5V -0.5 -0.8 mA

VOUT High VOH Vpin 2=2.3V, RL=15kΩ to GND 5 6 V

VOUT Low VOL Vpin 2=2.7V,Vpin 1=1.1V 0.7 1.1 V

UC3842A/3843A LINEAR INTEGRATED CIRCUIT

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 ELECTRICAL CHARACTERISTICS(Cont.)

PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT

Current Sense section

Gain GV (Note 2,3) 2.85 3 3.15 V/V

Maximum Input signal VI(MAX) Vpin 1=5V( Note 2) 0.9 1 1.1 V

PSRR

12≦VCC≦25V 70 dB

Input Bias Current IBIAS -2 -10 μA

Delay to Output Vpin 3=0 to 2V 150 300 ns

Output Section IO(SINK)=20mA 0.1 0.4 V

Low VOL IO(SINK)=200mA 1.5 2.2 V

IO(SOURCE)=20mA 13 13.5 V

Output Level High VOH IO(SOURCE)=200mA 12 13.5 V

Rise Time tR T

J=25°C,CL=1nF(Note 1) 50 150 ns

Fall Time tF T

J=25°C,CL=1nF(Note 1) 50 150 ns

Under-Voltage Lockout Output Section

3842A 14.5 16 17.5 V

Start Threshold 3843A VTH(ST) 7.8 8.4 9 V

3842A 8.5 10 11.5 V

Min. Operating Voltage 3843A VOPR(MIN) After Turn On 7 7.6 8.2 V

PWM Section MAX D(MAX) 95 97 100 %

Duty Cycle Min D(MIN) 0 %

Total Standby Curren t

Start-up Current IST 0.12 0.3 mA

Operating Supply Current ICC(OPR) Vpin 2=Vpin 3=0V 11 17 mA

VCC Zener Voltage Vz I

CC=25mA 34 V

Note:1.These parameters, although guaranteed ,are not 100% tested in producti on.

2. Parameters measured at trip point of latch with Vpin 2=0.

3. Gain defined as:

4. Adjust VCC above the start threshold before setting at 15V.

UC3842A/3843A LINEAR INTEGRATED CIRCUIT

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 OPEN-LOOP LABORATORY TEST FIXTURE

High peak current associated with capacity loads necessitate careful grounding techniques. Timing and bypass

capacitors should be connect ed close to pin 5 in single point GND. The transistor and 5kΩ potentio-meter are used

to sample the oscillator waveform and apply an adjustable Ramp to Pin 3.

 UNDER-VOLTAGE LOCKOUT

During Under-Voltage Lockout, the output driver is biased to a high impedance state. Pin 6 should be shunt to

GND with a bleeder resistor to prevent activat ing the power switch with output leakage currents.

 ERROR AMPLIFIER CONFIGURATION

2

1

0.5mA

2.5V

Zf

Zi

Error amplifier can source or sink up to 0.5mA

UC3842A/3843A LINEAR INTEGRATED CIRCUIT

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 CURRENT SENS E CIRCUIT

5

3

1

2R

R1V

CRs

R

Is

Error Amplifier

Current Sense Comparator

Peak current (Is) determined by the formula: Ismax=10V/Rs.

A small RC filter be required to suppress switch transients.

 SLOPE COMPENSATION

0.1 F

A fraction of the oscillator ramp can be resistively summed with the current sense signal to provide slope

compensation for converts requiring duty cycles over 50%.Note that capacitor C, forms a filter with R2 to suppress

the leading edge s witch spikes.

 OSCILLATOR SECTION

Dead time vs. CT(RT>5kΩ) Timing Resistance vs. Frequency

td (μs)

RT (kΩ)

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 SHUTDOWN TECHNIQUES

8

3

330Ω

500Ω

1kΩ1

Shutdown To current

Sense resistor

Shutdown

Shutdown UTC UC3842A can be accomplished by two methods; either raise pin 3 above 1V or pull Pin 1 below a

voltage two diode drops above ground. Either method caused the output of PWM comparator to be high(refer to

block diagram).The PW M latch is reset dominant so th at the output will remain low until the ne xt clock cycle after the

shutdown condition at pins 1 and/or 3 is removed . In one example, an externally latched shut –down may be

accomplished by adding an SCR which be reset by cycling VCC below the lower UVLO threshold. At this point the

reference turns off allowing the SCR to reset.

UC3842A/3843A LINEAR INTEGRATED CIRCUIT

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 TYPICAL CHARACTERISTICS

Output Saturation Characteristics Error Amplifier Open-Loop Frequency Response

Saturation Voltage (V)

Voltage Gain (dB)

PHASE (Degree)

-50 -25 0 25 50 75 100 125 150

4.96

4.97

4.98

4.99

5.00

5.01

5.02

Temperature (℃)

Vcc=15V

IOUT=1mA

-50 -25 0 25 50 75 100 125 150

250

300

350

400

450

500

550

Temperature (℃)

Vcc=9V

VREF Temperature Drift Istart Temperature Drift

UC3842A/3843A LINEAR INTEGRATED CIRCUIT

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UTC assumes no responsibility for equipment failures that result from using products at values that

exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or

other parameters) listed in products specifications of any and all UTC products described or contained

herein. UTC products are not designed for use in life support appliances, devices or systems where

m alfunction of these products can be reasonably expected to result in personal injury. Reproduction in

whole or in part is prohibited without the prior written consent of the copyright owner. The information

presented in this document does not form part of any quotation or contract, is believ ed to be accurate

and reliable and m ay be changed without notice.