ON Semiconductor UC2 3842, UC3843A, UC2842A, UC2843A Service Manual

UC3842A, UC3843A, UC2842A, UC2843A

High Performance Current Mode Controllers

The UC3842A, UC3843A series of high performance fixed frequency current mode controllers are specifically designed for off–line and dc–to–dc converter applications offering the designer a cost effective solution with minimal 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 totem pole output ideally suited for driving a power MOSFET.

Also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycle–by–cycle current limiting, programmable output deadtime, and a latch for single pulse metering.

These devices are available in an 8–pin dual–in–line plastic package as well as the 14–pin plastic surface mount (SO–14). The SO–14 package has separate power and ground pins for the totem pole output stage.

The UCX842A has UYLO thresholds of 16 V (on) and 10 V (off), ideally suited for off–line converters. The UCX843A is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and

7.6 V (off).

• Trimmed Oscillator Discharge Current for Precise Duty Cycle

Control

• Current Mode Operation to 500 kHz

• Automatic Feed Forward Compensation

• Latching PWM for Cycle–By–Cycle Current Limiting

• Internally Trimmed Reference with Undervoltage Lockout

• High Current Totem Pole Output

• Undervoltage Lockout with Hysteresis

• Low Startup and Operating Current

• Direct Interface with ON Semiconductor SENSEFET Products

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8

1

14

8

PIN CONNECTIONS

Compensation

Voltage Feedback

Current Sense

R

T/CT

Compensation

NC

Voltage Feedback

NC

Current Sense

NC

R

T/CT

PDIP–8 N SUFFIX CASE 626

SO–14

D SUFFIX

CASE 751A

1

SO–8

D1 SUFFIX

(Top View)

CASE 751

8

V

ref

7

V

CC

6

Output

Gnd

14

V

ref

13

NC

12

V

CC

11

V

C

10

Output

9

Gnd

Power Ground

8

1

2

3

45

1

2

3

4

5

6

7

 Semiconductor Components Industries, LLC, 2001

October, 2001 – Rev. 3

ORDERING INFORMATION

See detailed ordering and shipping information in the package dimensions section on page 15 of this data sheet.

DEVICE MARKING INFORMATION

See general marking information in the device marking section on page 16 of this data sheet.

1 Publication Order Number:

UC3842A/D

UC3842A, UC3843A, UC2842A, UC2843A

V

7(12)

CC

V

R

Voltage

Feedback

Input

Output

Compensation

ref

8(14)

TCT

4(7)

2(3)

1(1)

R

Oscillator

+

-

Error

Amplifier

Pin numbers in parenthesis are for the D suffix SO-14 package.

V

Undervoltage

Lockout

Gnd 5(9)

5.0V

Reference

ref

Latching

PWM

Figure 1. Simplified Block Diagram

MAXIMUM RATINGS

Rating Symbol Value Unit

Bias and Driver Voltages (Zero Series Impedance, see also Total Device spec) VCC, V Total Power Supply and Zener Current (ICC + IZ) 30 mA Output Current, Source or Sink (Note 1) I Output Energy (Capacitive Load per Cycle) W 5.0 µJ Current Sense and Voltage Feedback Inputs V Error Amp Output Sink Current I Power Dissipation and Thermal Characteristics

D Suffix, Plastic Package

Maximum Power Dissipation @ T Thermal Resistance, Junction–to–Air

N Suffix, Plastic Package

Maximum Power Dissipation @ T

Thermal Resistance, Junction–to–Air Operating Junction Temperature T Operating Ambient Temperature

UC3842A, UC3843A UC2842A, UC2843A

Storage Temperature Range T

1. Maximum Package power dissipation limits must be observed.

= 25°C

A

= 25°C

A

V

CC

Undervoltage

Lockout

V

7(11)

Output

6(10)

5(8)

3(5)

P

R

P

R

T

C

Power Ground

Current Sense Input

O

in

O

D

θ

JA

D

θ

JA J A

stg

C

– 0.3 to + 5.5 V

862 145

1.25 100

+ 150 °C

0 to + 70

– 25 to + 85

– 65 to + 150 °C

30 V

1.0 A

10 mA

mW

°C/W

W

°C/W

°C

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UC3842A, UC3843A, UC2842A, UC2843A

ELECTRICAL CHARACTERISTICS (V

= 15 V, [Note 2], RT = 10 k, CT = 3.3 nF, TA = T

CC

low

to T

[Note 3],

high

unless otherwise noted.)

UC284XA UC384XA

Characteristics Symbol Min Typ Max Min Typ Max Unit

REFERENCE SECTION

Reference Output Voltage (I

= 1.0 mA, TJ = 25°C) V

O

Line Regulation (VCC = 12 V to 25 V) Reg Load Regulation (IO = 1.0 mA to 20 mA) Reg Temperature Stability T Total Output Variation over Line, Load, Temperature V Output Noise Voltage (f = 10 Hz to 10 kHz,

= 25°C)

T

J

ref

line

load

S

ref

V

n

4.95 5.0 5.05 4.9 5.0 5.1 V – 2.0 20 – 2.0 20 mV – 3.0 25 – 3.0 25 mV – 0.2 – – 0.2 – mV/°C

4.9 – 5.1 4.82 – 5.18 V – 50 – – 50 – µV

Long Term Stability (TA = 125°C for 1000 Hours) S – 5.0 – – 5.0 – mV Output Short Circuit Current I

SC

– 30 – 85 – 180 – 30 – 85 – 180 mA

OSCILLATOR SECTION

osc/∆V

∆f

osc/∆T

I

dischg

f

osc

47 46

52

–

60

57

47 46

52

–

60

57

– 0.2 1.0 – 0.2 1.0 % – 5.0 – – 5.0 – %

– 1.6 – – 1.6 – V

7.5

7.2

8.4 –

9.5

9.3

7.5

7.2

8.4 –

9.5

9.3

Frequency

= 25°C

T

J

= T

T

to T

A

low

high

Frequency Change with Voltage (VCC = 12 V to 25 V) ∆f Frequency Change with Temperature

T

= T

to T

A

low

high

Oscillator Voltage Swing (Peak–to–Peak) V Discharge Current (V

T

= 25°C

J

= T

T

to T

A

low

high

= 2.0 V)

osc

ERROR AMPLIFIER SECTION

Voltage Feedback Input (V Input Bias Current (VFB = 2.7 V) I Open Loop Voltage Gain (VO = 2.0 V to 4.0 V) A

= 2.5 V) V

O

FB

IB

VOL

2.45 2.5 2.55 2.42 2.5 2.58 V – –0.1 –1.0 – –0.1 –2.0 µA

65 90 – 65 90 – dB Unity Gain Bandwidth (TJ = 25°C) BW 0.7 1.0 – 0.7 1.0 – MHz Power Supply Rejection Ratio (VCC = 12 V to 25 V) PSRR 60 70 – 60 70 – dB Output Current

Sink (V Source (V

= 1.1 V, VFB = 2.7 V)

O

= 5.0 V, VFB = 2.3 V)

O

I

Sink

I

Source

2.0

–0.512–1.0

– –

2.0

–0.512–1.0

– –

Output Voltage Swing

High State (R Low State (R

= 15 k to ground, VFB = 2.3 V)

L

= 15 k to V

L

, VFB = 2.7 V)

ref

V

OH

V

OL

5.0 –

0.8

6.2

1.1

–

5.0 –

0.8

6.2

–

1.1

2. Adjust VCC above the Startup threshold before setting to 15 V.

3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible. =0°C for UC3842A, UC3843A T

T

low

–25°C for UC2842A, UC2843A +85°C for UC2842A, UC2843A

= +70°C for UC3842A, UC3843A

high

kHz

mA

V

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3

UC3842A, UC3843A, UC2842A, UC2843A

ELECTRICAL CHARACTERISTICS (V

= 15 V, [Note 4], RT = 10 k, CT = 3.3 nF, TA = T

CC

low

to T

[Note 5],

high

unless otherwise noted.)

UC284XA UC384XA

Characteristics Symbol Min Typ Max Min Typ Max Unit

CURRENT SENSE SECTION

Current Sense Input Voltage Gain (Notes 6 & 7) Maximum Current Sense Input Threshold (Note 6) V Power Supply Rejection Ratio

= 12 to 25 V (Note 6)

V

CC

Input Bias Current I Propagation Delay (Current Sense Input to Output) t

A

V th

PSRR

IB

PLH(in/out)

2.85 3.0 3.15 2.85 3.0 3.15 V/V

0.9 1.0 1.1 0.9 1.0 1.1 V

– 70 – – 70 – – –2.0 –10 – –2.0 –10 µA – 150 300 – 150 300 ns

OUTPUT SECTION

Output Voltage

Low State (I

High State (I

= 20 mA)

Sink

= 200 mA)

Sink

= 20 mA)

Sink

= 200 mA)

Sink

Output Voltage with UVLO Activated

V

CC

= 6.0 V, I

= 1.0 mA

Sink

Output Voltage Rise Time (CL = 1.0 nF, TJ = 25°C) t Output Voltage Fall Time (CL = 1.0 nF, TJ = 25°C) t

V

OL

V

OH

V

OL(UVLO)

–

– 13 12

0.1

1.6

13.5

13.4

0.4

2.2

–

– – –

13 12

0.1

1.6

13.5

13.4

– 0.1 1.1 – 0.1 1.1

r f

– 50 150 – 50 150 ns – 50 150 – 50 150 ns

UNDERVOLTAGE LOCKOUT SECTION

Startup Threshold

UCX842A UCX843A

Minimum Operating Voltage After Turn–On

UCX842A UCX843A

V

CC(min)

th

15

7.8

9.0

7.0

16

8.4

10

7.6

17

9.0

11

8.2

14.5

7.8

8.5

7.0

16

8.4

10

7.6

PWM SECTION

Duty Cycle

Maximum Minimum

DC

max

min

94

–

96

– 0

94

–

96

TOTAL DEVICE

Power Supply Current (Note 4)

I

CC

Startup: (VCC = 6.5 V for UCX843A,

= 14 V for UCX842A) Operating

(V

CC

Power Supply Zener Voltage (ICC = 25 mA) V

Z

– –

0.5 12

1.0 17

– –

0.5 12

30 36 – 30 36 – V

4. Adjust VCC above the Startup threshold before setting to 15 V.

5. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible. =0°C for UC3842A, UC3843A T

T

low

–25°C for UC2842A, UC2843A +85°C for UC2842A, UC2843A

= +70°C for UC3842A, UC3843A

high

6. This parameter is measured at the latch trip point with VFB = 0 V.

7. Comparator gain is defined as: A

∆V Output Compensation

V

∆V Current Sense Input

dB

V

0.4

2.2 – –

V

17.5

9.0

V

11.5

8.2

% – 0

mA

1.0 17

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UC3842A, UC3843A, UC2842A, UC2843A

80

50

Ω, TIMING RESISTOR (k )

20

8.0

5.0

VCC = 15 V

2.0

T

R

T

= 25°C

A

0.8 10 k 20 k 50 k 100 k 200 k 500 k 1.0 M

f

, OSCILLATOR FREQUENCY (Hz)

OSC

Figure 2. Timing Resistor versus

Oscillator Frequency

9.0

VCC = 15 V V

= 2.0 V

OSC

8.5

100

VCC = 15 V

50

T

= 25°C

A

20

10

5.0

2.0

% DT, PERCENT OUTPUT DEADTIME

1.0 10 k 20 k 50 k 100 k 200 k 500 k 1.0 M

, OSCILLATOR FREQUENCY (Hz)

f

OSC

Figure 3. Output Deadtime versus

Oscillator Frequency

100

VCC = 15 V CT = 3.3 nF

90

T

= 25°C

A

I

dischg

= 7.2 mA

80

8.0

, DISCHARGE CURRENT (mA)

7.5

dischg

I

7.0

-55 -25 0 25 50 75 100 125

, AMBIENT TEMPERATURE (°C)

T

A

Figure 4. Oscillator Discharge Current

versus Temperature

VCC = 15 V

2.55 V

2.5 V

AV = -1.0 T

= 25°C

A

, MAXIMUM OUTPUT DUTY CYCLE (%)

D

3.0 V

2.5 V

20 mV/DIV

70

60

50

max

40

I

dischg

= 9.5 mA

800 1.0 k 2.0 k 3.0 k 4.0 k 6.0 k 8.0 k

R

, TIMING RESISTOR (Ω)

T

Figure 5. Maximum Output Duty Cycle

versus Timing Resistor

VCC = 15 V AV = -1.0 T

= 25°C

A

200 mV/DIV

2.45 V

0.5 µs/DIV

Figure 6. Error Amp Small Signal

Transient Response

2.0 V

0.1 µs/DIV

Figure 7. Error Amp Large Signal

Transient Response

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UC3842A, UC3843A, UC2842A, UC2843A

)

100

80

Gain

60

40

20

, OPEN LOOP VOLTAGE GAIN (dB)

0

VOL

A

-20 100 1.0 k 10 k 100 k 1.0 M

f, FREQUENCY (Hz)

Figure 8. Error Amp Open Loop Gain and

Phase versus Frequency

0

-4.0

-8.0

VCC = 15 V VO = 2.0 V to 4.0 V RL = 100 K T

= 25°C

A

Phase

VCC = 15 V

0

30

60

90

120

150

180

10 M10

1.2

1.0

0.8

0.6

0.4

, EXCESS PHASE (DEGREES)

0.2

φ

, CURRENT SENSE INPUT THRESHOLD (V

th

0

V

110

90

VCC = 15 V

T

= 25°C

A

T

= 125°C

A

T

= -55°C

A

0

2.0 4.0 6.0 8.0 , ERROR AMP OUTPUT VOLTAGE (V)

V

O

Figure 9. Current Sense Input Threshold

versus Error Amp Output Voltage

VCC = 15 V R

≤ 0.1 Ω

L

-12

T

-16

-20

ref

V ∆ , REFERENCE VOLTAGE CHANGE (mV)

-24 0 20 40 60 80 100 120

= 125°C

A

T

= 25°C

A

I

, REFERENCE SOURCE CURRENT (mA)

ref

T

A

= 55°C

Figure 10. Reference Voltage Change

versus Source Current

VCC = 15 V IO = 1.0 mA to 20 mA T

= 25°C

A

70

, REFERENCE SHORT CIRCUIT CURRENT (mA)

50

SC

I

-55 -25 0 25 50 75 100 125

T

, AMBIENT TEMPERATURE (°C)

A

Figure 11. Reference Short Circuit Current

versus Temperature

VCC = 12 V to 25 V T

= 25°C

A

O

V ∆ , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)

Figure 12. Reference Load Regulation

2.0 ms/DIV

O

V ∆ , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)

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2.0 ms/DIV

Figure 13. Reference Line Regulation