UC3842D - Philips Semiconductors / NXP Semiconductors

Philips Semiconductors Linear Products Product specification

UC3842Current-mode PWM controller

1100

August 31, 1994 853-0614 13721

DESCRIPTION

The UC3842 is available in an 8-Pin mini-DIP the necessary

features to implement off-line, fixed-frequency current-mode control

schemes with a minimal external parts count. This technique results

in improved line regulation, enhanced load response characteristics,

and a simpler, easier to design control loop. Topological advantages

include inherent pulse-by-pulse current limiting.

Protection circuitry includes built-in undervoltage lock-out and

current limiting. Other features include fully-latched operation, a 1%

trimmed bandgap reference, and start-up current less than 1mA.

These devices feature a totem-pole output designed to source and

sink high peak current from a capacitive load, such as the gate of a

power MOSFET. Consistent with N-channel power devices, the

output is low in the OFF-state.

FEATURES

•Low start-up current (≤1mA)

•Automatic feed-forward compensation

•Pulse-by-pulse current limiting

•Enhanced load response characteristics

•Undervoltage lock-out with hysteresis

•Double pulse suppression

•High current totem-pole output

•Internally-trimmed bandgap reference

•400kHz operation, guaranteed min

PIN CONFIGURATIONS

N Package

D Package

4 5

7 8

COMP

VFB

ISENSE

RT/CT

VFB

ISENSE

RT/CT

VREF

VCC

OUTPUT

GROUND

VREF

VCC

OUTPUT

GROUND

POWER GROUND

TOP VIEW

APPLICATIONS

•Off-line switched mode power supplies

•DC-to-DC converters UC3842

BLOCK DIAGRAM

NOTE:

Pin numbers in parentheses refer to the D package.

(12)7

(9)5

(7)4

(3)2

(1)1

(5)3

7(11)

8(14)

6(10)

5(8)

GND

COMP

CURRENT

SENSE

CURRENT

SENSE

COMPARATOR

PWM

LATCH

INTERNAL

BIAS

REF

UVLO

34V

16V

OSC

ERROR

AMP

–

2.5V

5.0V

50mA

OUTPUT

VREF

VCC

VFB

S/R

RT/CT

Philips Semiconductors Linear Products Product specification

UC3842Current-mode PWM controller

August 31, 1994 1101

ORDERING INFORMATION

DESCRIPTION TEMPERATURE RANGE ORDER CODE DWG #

8-Pin Plastic Dual In-Line Package (DIP) 0 to +70°C UC3842N 0404B

14-Pin Plastic Small Outline (SO) Package 0 to +70°C UC3842D 0405B

ABSOLUTE MAXIMUM RATINGS1

SYMBOL PARAMETER RATING UNIT

VCC Supply voltage (ICC<30mA) Self-Limiting

VCC Supply voltage

(low impedance source) 30 V

IOUT Output current 2, 3±1 A

Output energy (capacitive load) 5 µJ

Analog inputs (Pin 2, Pin 3) -0.3 to 6.3 V

Error amp output sink current 10 mA

PDPower dissipation at TA≤70°C 1 W

(derate 12.5mW/°C for TA>70°C)2

TSTG Storage temperature range -65 to +150 °C

TSOLD Lead temperature

(soldering, 10sec max) 300 °C

NOTES:

1. All voltages are with respect to Pin 5; all currents are positive into the specified terminal.

2. See section in application note on “Power Dissipation Calculation”.

3. This parameter is guaranteed, but not 100% tested in production.

Philips Semiconductors Linear Products Product specification

UC3842Current-mode PWM controller

August 31, 1994 1102

DC AND AC ELECTRICAL CHARACTERISTICS

0≤TJ≤70°C for UC3842; VCC=15V; RT=10kW; CT=3.3nF, unless otherwise specified.

SYMBOL

PARAMETER

TEST CONDITIONS

UC3842

UNIT

SYMBOL

PARAMETER

TEST CONDITIONS

Min Typ Max

UNIT

Reference section

VOUT Output voltage TJ=25°C, IO=1mA 4.90 5.00 5.10 V

Line regulation 12≤VIN≤25V 6 20 mV

Load regulation 1≤IO≤20mA 6 25 mV

Temp. stability10.2 0.4 mV/°C

Total output variation1Line, load, temp. 4.82 5.18 V

VNOISE Output noise voltage110Hz≤f≤10kHz, TJ=25°C 50 µV

Long-term stability1TJ=125°C, 1000 Hrs. 5 25 mV

Output short-circuit TJ=25 -30 -100 -130 mA

Output short-circuit -55<TJ≤0°C -30 -100 -180 mA

Oscillator section

Initial accuracy TJ=25°C 47 52 57 kHz

Voltage stability 12≤VCC≤25V 0.2 1 %

Temp. stability1TMIN≤TJ≤TMAX 5 %

Amplitude VPIN 4 peak-to-peak 1.7 V

Error amp section

Input voltage V Pin 1=2.5V 2.42 2.50 2.58 V

IBIAS Input bias current -0.3 -2 µA

AVOL 2≤VO≤4V 65 90 dB

Unity gain bandwidth1TJ=25°C 0.7 1 MHz

Unity gain bandwidth TMIN<TJ<TMAX 0.5 MHz

PSRR Power supply rejection ratio 12≤VCC≤25V 60 70 dB

ISINK Output sink current VPIN 2=2.7V, VPIN 1=1.1V 2 6 mA

ISOURCE Output source current VPIN 2=2.3V, VPIN 1=5V -0.5 -0.8 mA

VOUT High VPIN 2=2.3V, RL=15k to ground 5 6 V

VOUT Low VPIN 2=2.7V, RL=15k to Pin 8 0.7 1.1 V

Current sense section

Gain 2, 32.85 3 3.15 V/V

Maximum input signal2VPIN 1=5V 0.9 1 1.1 V

PSRR Power supply rejection ratio212≤VCC≤25V 70 dB

IBIAS Input bias current -2 -10 µA

Delay to output1150 300 ns

Philips Semiconductors Linear Products Product specification

UC3842Current-mode PWM controller

August 31, 1994 1103

DC AND AC ELECTRICAL CHARACTERISTICS

0≤TJ≤70°C for UC3842; VCC=154; RT=10kΩ; CT=3.3nF, unless otherwise specified

SYMBOL

PARAMETER

TEST CONDITIONS

UC3842

UNIT

SYMBOL

PARAMETER

TEST CONDITIONS

Min Typ Max

UNIT

Output section

VOL

Output Low-Level

ISINK=20mA 0.1 0.4

VOL

Output Low-Level

ISINK=200mA 1.5 2.2

VOH

Output High-Level

ISOURCE=20mA 13 13.5

VOH

Output High-Level

ISOURCE=200mA 12 13.5

tRRise time CL=1nF 50 150 ns

tFFall time CL=1nF 50 150 ns

Undervoltage lockout section

Start threshold 14.5 16 17.5 V

Min. operating voltage after turn on 8.5 10 11.5 V

PWM section

Maximum duty cycle 93 97 100

Minimum duty cycle 0

Total standby current

Start-up current 0.5 1 mA

ICC Operating supply current VPIN 2=VPIN 3=0V 11 17 mA

VCC zener voltage ICC=25mA 34 V

Maximum operating frequency section

Maximum operating frequency for all

functions operating cycle-by-cycle 400 kHz

NOTES:

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

2. Parameter measured at trip point of latch with VPIN 2=0.

3. Gain defined as: A

VPIN 1

VPIN 3; 0 VPIN 30.8V

UNDERVOLTAGE LOCKOUT

UC3842

VON 16V

VOFF 10V

NOTE:

During Undervoltage 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.

VCC ON/OFF COMMAND

TO REST OF IC

VCC

VOFF VON

ICC

<15mA

<1mA

ERROR AMP CONFIGURATION

NOTE:

Error AMP can source or sink up to 0.5mA.

2.5V 0.5mA

COMP

VFB

–

Philips Semiconductors Linear Products Product specification

UC3842Current-mode PWM controller

August 31, 1994 1104

CURRENT SENSE CIRCUIT

NOTE:

Peak current (IS) is determined by the formula:

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

ISMAX 1.0V

ERROR

AMP

CURRENT

SENSE

COMPARATOR

COMP

CURRENT

SENSE

GND

TYPICAL PERFORMANCE CHARACTERISTICS

Output Saturation Characteristics Error Amplifier Open-Loop

Frequency Response

VOLTAGE GAIN (dB)

FREQUENCY (Hz)

PHASE (DEG)

100

–2010 100 1k 10k 100k 1M 10M

–45

–90

–135

–180

–225

SATURATION VOLTAGE (V)

0.01 0.03 0.05 0.1 0.3 0.5 1.0

OUTPUT CURRENT, SOURCE OR SINK (A)

0Av

Philips Semiconductors Linear Products Product specification

UC3842Current-mode PWM controller

August 31, 1994 1105

OPEN-LOOP LABORATORY TEST FIXTURE

NOTE:

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.

4.7k

ERROR AMP

ADJUST

4.7k

2N2222

100k

ADJUST

COMP

OUTPUT

GND

OUTPUT

GND

VREF

VCC

UC3842

VFB

ISENSE

RT/CT

VREF

VCC 0.1µF

ISENSE

0.1µF

SHUTDOWN TECHNIQUES

NOTE:

Shutdown of the UC3842 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 causes the

output of the 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 the examples shown, an externally-latched shutdown may be accomplished by adding an SCR which will be reset by cycling

VCC below the lower UVLO threshold (10V). At this point all internal bias is removed, allowing the SCR to reset.

COMP

SHUTDOWN

TO CURRENT

SHUTDOWN

SENSE RESISTOR

4.7k

4.7k 8

500 ISENSE

Philips Semiconductors Linear Products Product specification

UC3842Current-mode PWM controller

August 31, 1994 1106

OFF-LINE FLYBACK REGULATOR

UC3842

4.7 1W

673-3

INPUT

250V

56k

16V

20k

150k

3.6k 100pF

COMP

10k

GND

CUR

SEN

OUT

20k

0.85

UFN432

1N3613

ISOLATION

BOUNDARY

2.5k

820pF

1N3613

400V

4.7k

T1 USD735

10V DC

OUT (5V 2–5A)

–

220µF

10µF

20V

0.01µF

0.0047µF

0.01µF

4700µF

470pF

VFB

VREF

RT/CT

VCC

NOTES:

T1: Coilcraft E-4140-B

Primary – 97 turns

single AWG24

Secondary – 4 turns

4 parallel

AWG22

control – 9 turns

–3 parallel AWG28

SPECIFICATIONS

Input line voltage: 90VAC to 130VAC

Input frequency: 50 or 60Hz

Switching frequency: 40kHz±10%

Output power: 25W maximum

Output voltage: 5V±5%

Output current: 2 to 5A

Line regulation: 0.01%/V

Load regulation: 8%/A*

Efficiency @ 25 W,

VIN=90VAC: 70%

VIN=130VAC: 65%

Output short-circuit current: 2.5A average

NOTE:

This circuit uses a low-cost feedback scheme in which the DC

voltage developed from the primary-side control winding is sensed

by the UC3842 error amplifier. Load regulation is therefore

dependent on the coupling between secondary and control

windings, and on transformer leakage inductance. For applications

requiring better load regulation, a UC1901 Isolated Feedback

Generator can be used to directly sense the output voltage.

Philips Semiconductors Linear Products Product specification

UC3842Current-mode PWM controller

August 31, 1994 1107

SYNCHRONIZATION AND MAXIMUM DUTY CYCLE CLAMP

NOTES:

f+1.44

(RA)2RB) C

DMAX +

RA)2RB

GND

OUT

RESET

DISCH

TRIG

THRESH

NE555

UC3842

TO OTHER

UC3842s

GND

VCC

RT/CT