UC3842A - Contek Microelectronics Co., Ltd.

UC3842A /3843A LINEARINTEGRATED CIRCUIT

CURRENT MODE PWM CONTROL

CIRCUITS

DESCRIPTION

The Contek UC3842A/3843A provide the necessary functions

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

mode , controlled switching circuits with a minimal external

part count

FEATURES

*Low external part count.

*Low start up current ( Typical 0.12mA )

*Automatic feed forward compensation

*Pulse-by-Pulse current limiting

*Under-voltage lockout with hysteresis

*Double pulse Suppression

*High current totem pole output to drive MOSFET directly

*Internally trimmed band gap reference

*500kHz operation

DIP-8

SOP-8

BLOCK DIAGRAM

Internal

Bias

5V REF S/R

U.V.L.O

PWM

LATCH

Vref

Good

Logic

ERROR

AMPLIFIER

1/2Vref

1/3Vref

OSCILLATOR

Vref

VFB

COMP

CURRENT SENSE

RT/CT

Vcc

GND

OUTPUT

Vcc

GND

CURRENT

SENSE

COMPARATOR

ABSOLUTE MAXIMUM RATINGS(Ta=25 C)

PARAMETER SYMBOL VALUE UNIT

Supply Voltage(Low Impedance Source) VCC 30 V

Supply Voltage(Icc<30mA) Vcc Self Limiting V

Output Current ( Peak ) Io +-1 A

Output Energy(capacity Load) 5 mJ

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

Error Amplifier Output Sink Current ISINK(EA) 10 mA

Power Dissipation PD DIP-8 at Tamb<=25 C 1.0 W

SOP-8 at Tamb<=25 C 0.5 W

Lead Temperature( Soldering 10 Sec ) Tlead 300 C

Contek

CONTEK

Contek Microelectronics Co.,Ltd.

http://www.contek-ic.com E-mail:sales@contek-ic.com

UC3842A /3843A LINEARINTEGRATED CIRCUIT

(continued)

PARAMETRER SYMBOL VALUE UNIT

Storage Temperature Tstg -65 ~ +150 C

Note 1: Ta>25 C, PDderated with 8mW/ C.

ELECTRICAL CHARACTERISTICS(0 C <=Ta<=70 C,VCC=15V,RT=10kW,CT=3.3nF,unless otherwise

specified)

PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT

Reference Section

Output Voltage VREF Tj=25 C,Io=1mA 4.9 5 5.1 V

Line Regulation DVREF 12<=VIN<=25V 6 20 mV

Load Regulation DVREF 1<=Io=20mA 6 25 mV

Temperature Stability (Note 2) 0.2 0.4 mV/ C

Total Output Variation Line, Load, Temp(note 2) 4.82 5.18 V

Output Noise Voltage Vosc 10Hz<=f<=10kHz,Tj=25 C (note 2) 50 uV

Long Term Stability Ta=25 C,1000Hrs(note 2) 525mV

Output Short Circuit ISC -30 -100 -180 mA

Oscillator Section

Initial Accuracy f Tj=25 C 47 52 57 kHz

Voltage Stability Df/DVcc 12<=Vcc<=25V 0.2 1 %

Temperature Stability Tmin<=TA<=Tmax(note 2) 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 IBIAS -0.3 -2 mA

AVOL 2 <=Vo<=4V 60 90 dB

Unity Gain Bandwidth Tj=25 C (note 2) 0.7 1 MHz

PSRR I2<=Vcc<=25V 60 70 dB

Output Sink Current Isink Vpin 2=2.7V,Vpin 1=1.1V 2 6 mA

Output Source Current Isource Vpin 2=2.3V,Vpin 1=5V -0.5 -0.8 mA

Vout High VOH Vpin 2=2.3V, RL=15kWto GND 56 V

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

Current Sense section

Gain GV(note 3,4) 2.85 3 3.15 V/V

Maximum Input signal VI(MAX) Vpin 1=5V( note 3) 0.9 1 1.1 V

PSRR 12<=Vcc<=25V 70 dB

Input Bias Current IBIAS -2 -10 mA

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

Output Section

Output Low Level VOL Isink=20mA 0.1 0.4 V

Isink=200mA 1.5 2.2 V

Output High Level VOH Isource=20mA 13 13.5 V

Isource=200mA 12 13.5 V

Rise Time tRTj=25 C,CL=1nF(note 2) 50 150 ns

Fall Time tFTj=25 C,CL=1nF(note 2) 50 150 ns

Under-Voltage Lockout Output Section

Start Threshold VTH(ST) Contek 3842A 14.5 16 17.5 V

Contek 3843A 7.8 8.4 9 V

Min. Operating Voltage VOPR(min) After Turn On

Contek 3842A

8.5 10 11.5

Contek 3843A 7 7.6 8.2 V

PWM Section

Maximum Duty Cycle D(MAX) 95 97 100 %

CONTEK

Contek Microelectronics Co.,Ltd.

http://www.contek-ic.com E-mail:sales@contek-ic.com

UC3842A /3843A LINEARINTEGRATED CIRCUIT

PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT

Minimum Duty Cycle D(MIN) 0%

Total Standby Current

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 Icc=25mA 34 V

note 2:These parameters, although guaranteed ,are not 100% tested in production.

note 3:Parameters measured at trip point of latch with Vpin 2=0.

note 4:Gain defined as:

DVpin 1

DVpin 3

A= ; 0<=Vpin3<=0.8V

note 5:Adjust Vcc above the start threshold before setting at 15V.

OPEN-LOOP LABORATORY TEST FIXTURE

3 6

4 5

Vref

Vcc

1kW

/1W

0.1 mF

100kW

5kW

4.7kW4.7kW

0.1 mF

Error Amp

Adjust

Isense

Adjust

OUTPUT

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

capacitors should be connected close to pin 5 in single point GND. The transistor and 5kWpotentio-meter are used to

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

UNDER-VOLTAGE LOCKOUT

Vcc

Von=16V

Voff=10V

ON/OFF Command

to rest of IC

Von Voff

<1mA

>15mA

Icc

Vcc

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 activating the power switch with output leakage currents.

Contek

CONTEK

Contek Microelectronics Co.,Ltd.

http://www.contek-ic.com E-mail:sales@contek-ic.com

UC3842A /3843A LINEARINTEGRATED CIRCUIT

ERROR AMPLIFIER CONFIGURATION

0.5mA

2.5V

Error amplifier can source or sink up to 0.5mA

CURRENT SENSE CIRCUIT

R1V

CRs

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

IsenseR1 R2

Rsense

0.1 mF

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 switch spikes.

Contek

CONTEK

Contek Microelectronics Co.,Ltd.

http://www.contek-ic.com E-mail:sales@contek-ic.com

UC3842A /3843A LINEARINTEGRATED CIRCUIT

OSCILLATOR SECTION

Large RT

Small CT

Small RT

Large CT

INTERNAL

CLOCK

INTERNAL

CLOCK

Dead time VS C T(RT>5kW) Timing Resistance Vs Frequency

100

1 10 100

0.1

td (ms)

CT (nF)

100

1010 2

RT (k W)

Frequency (Hz)

CT=1nF

CT=2.2nF

CT=4.7nF

CT=10nF

CT=22nF

CT=47nF

CT=100nF

SHUTDOWN TECHNIQUES

330W

500W

1kW1

Shutdown To current

Sense resistor

Shutdown

Shutdown Contek 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

PWM latch is reset dominant so that the output will

remain low until the next 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.

CONTEK

Contek Microelectronics Co.,Ltd.

http://www.contek-ic.com E-mail:sales@contek-ic.com

UC3842A /3843A LINEARINTEGRATED CIRCUIT

TYPICAL PERFORMANCE CHARACTERISTICS

0.01 0.1 1

Saturation Voltage (V)

Output Current

(Sourse or Sink Current) (A)

Vcc=15V

Ta=+25 C

Ta=-55 C

10 6

10102

100

Frequency (Hz)

Voltage Gain (dB)

-180

-135

-90

-45

PHASE (Degree)

Output Saturation Characteristics Error Amplifier Open-Loop Frequency Response

-50 -25 0 25 50 75 100 125 150

4.96

4.97

4.98

4.99

5.00

5.01

5.02

Vref (V)

Temperature ( C)

Vcc=15V

Io=1mA

-50 -25 0 25 50 75 100 125 150

250

300

350

400

450

500

550

Istart (mA)

Temperature ( C)

Vcc=9V

-50 -25 0 25 50 75 100 125 150

Icc (mA)

Temperature ( C)

Vcc=15V

Io=1mA

Vref TemperatureDrift IstartTemperatureDrift

Icc TemperatureDrift

CONTEK

Contek Microelectronics Co.,Ltd.

http://www.contek-ic.com E-mail:sales@contek-ic.com