Motorola UC3843AN, UC3843AD, UC3842AN Datasheet

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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 Motorola SENSEFET Products

Simplified Block Diagram

V

7(12)

CC

V

ref

8(14)

RTC

4(7)

Voltage

Feedback

Input

2(3)

Output

Compensation

1(1)

5.0V

R

T

Oscillator

+ –

Error

Amplifier

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

Undervoltage

Lockout

Gnd 5(9)

Reference

V

ref

Latching

PWM

V

CC

Undervoltage

Lockout

V

C

7(11)

Output

6(10)

Power Ground

5(8)

3(5)

Current Sense Input

Order this document by UC3842A/D

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HIGH PERFORMANCE

CURRENT MODE

CONTROLLERS

N SUFFIX

PLASTIC PACKAGE

CASE 626

D SUFFIX

PLASTIC PACKAGE

CASE 751A

(SO–14)

Compensation

Voltage Feedback

Current Sense

RT/C

Compensation

Voltage Feedback

Current Sense

RT/C

ORDERING INFORMATION

Device

UC3842AD UC3843AD UC3842AN UC3843AN UC2842AD UC2843AD UC2842AN UC2843AN

Temperature Range

TA = – 25° to +85°C

PIN CONNECTIONS

1 2 3

45

T

1 2

NC

3 4

NC

5 6

NC

7

T

Operating

TA = 0° to +70°C

8

(T op View)

(T op V iew)

1

14

1

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

Package

SO–14 SO–14 Plastic Plastic SO–14 SO–14 Plastic Plastic

MOTOROLA ANALOG IC DEVICE DATA

 Motorola, Inc. 1996 Rev 1

1

UC3842A, 43A UC2842A, 43A

MAXIMUM RATINGS

Rating Symbol Value Unit

Total Power Supply and Zener Current (ICC + IZ) 30 mA Output Current, Source or Sink (Note 1) I

O

Output Energy (Capacitive Load per Cycle) W 5.0 µJ Current Sense and Voltage Feedback Inputs V Error Amp Output Sink Current I

in

O

Power Dissipation and Thermal Characteristics

D Suffix, Plastic Package

Maximum Power Dissipation @ TA = 25°C Thermal Resistance, Junction–to–Air

N Suffix, Plastic Package

Maximum Power Dissipation @ TA = 25°C

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

UC3842A, UC3843A

P

D

R

θJA

P

D

R

θJA

J

T

A

UC2842A, UC2843A

Storage Temperature Range T

stg

1.0 A

– 0.3 to + 5.5 V

10 mA

862 145

1.25 100

+ 150 °C

0 to + 70

– 25 to + 85

– 65 to + 150 °C

mW

°C/W

W

°C/W

°C

ELECTRICAL CHARACTERISTICS (V

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

CC

low

to T

high

[Note 3],

unless otherwise noted.)

UC284XA UC384XA

Characteristics Symbol Min Typ Max Min Typ Max Unit

REFERENCE SECTION

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

ref

line load S

ref

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

Frequency

TJ = 25°C TA = T

low

to T

high

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

TA = T

low

to T

high

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

TJ = 25°C

TA = T

NOTES: 1. Maximum Package power dissipation limits must be observed.

to T

low

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 T

= –20°C for UC3842A, UC3843A T

low

T

= –25°C for UC2842A, UC2843A T

low

high

osc

= 2.0 V)

f

osc

47 46

osc/∆V

∆f

osc/∆T

I

dischg

osc

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

– 1.6 – – 1.6 – V

7.5

7.2

= +70°C for UC3842A, UC3843A

high

= +85°C for UC2842A, UC2843A

high

52

8.4

–

60

9.3

57

–

9.5

47 46

7.5

7.2

52

8.4

–

60

9.3

57

–

9.5

kHz

mA

2

MOTOROLA ANALOG IC DEVICE DATA

UC3842A, 43A UC2842A, 43A

ELECTRICAL CHARACTERISTICS (V

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

CC

low

to T

high

[Note 3],

unless otherwise noted.)

UC284XA UC384XA

Characteristics Symbol Min Typ Max Min Typ Max Unit

ERROR AMPLIFIER SECTION

Voltage Feedback Input (VO = 2.5 V) V Input Bias Current (VFB = 2.7 V) I Open Loop Voltage Gain (VO = 2.0 V to 4.0 V) A

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 (VO = 1.1 V, VFB = 2.7 V) Source (VO = 5.0 V, VFB = 2.3 V)

I

Sink

I

Source

2.0

–0.512–1.0

– –

2.0

–0.512–1.0

– –

Output Voltage Swing

High State (RL = 15 k to ground, VFB = 2.3 V) Low State (RL = 15 k to V

, VFB = 2.7 V)

ref

V

OH

V

OL

5.0 –

6.2

0.8

1.1

–

5.0 –

0.8

6.2

–

1.1

CURRENT SENSE SECTION

Current Sense Input Voltage Gain (Notes 4 & 5) A Maximum Current Sense Input Threshold (Note 4) V Power Supply Rejection Ratio

PSRR

VCC = 12 to 25 V (Note 4) Input Bias Current I Propagation Delay (Current Sense Input to Output) t

PLH(in/out)

V

th

IB

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

Output Voltage with UVLO Activated

VCC = 6.0 V, I Output Voltage Rise T ime (CL = 1.0 nF, TJ = 25°C) t Output Voltage Fall T ime (CL = 1.0 nF, TJ = 25°C) t

Sink Sink Sink

Sink

= 20 mA) = 200 mA) = 20 mA) = 200 mA)

= 1.0 mA

V

OL

V

OH

V

OL(UVLO)

r f

–

– 13 12

0.1

1.6

13.5

13.4

0.4

2.2

–

– – –

13 12

0.1

1.6

13.5

13.4

0.4

2.2 – –

– 0.1 1.1 – 0.1 1.1 – 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

th

V

CC(min)

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

17.5

9.0

11.5

8.2

PWM SECTION

Duty Cycle

Maximum Minimum

DC

max

min

94

–

96

– 0

94

–

96

– 0

TOTAL DEVICE

Power Supply Current (Note 2)

Startup: (VCC = 6.5 V for UCX843A,

(VCC = 14 V for UCX842A) Operating

Power Supply Zener Voltage (ICC = 25 mA) V

NOTES: 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 T

= –20°C for UC3842A, UC3843A T

low

T

= –25°C for UC2842A, UC2843A T

low

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

5.Comparator gain is defined as: A

∆V Output Compensation

V

∆V Current Sense Input

I

CC

– –

Z

= +70°C for UC3842A, UC3843A

high

= +85°C for UC2842A, UC2843A

high

30 36 – 30 36 – V

0.5 12

1.0 17

– –

0.5 12

1.0 17

mA

V

dB

V

%

mA

MOTOROLA ANALOG IC DEVICE DATA

3

UC3842A, 43A UC2842A, 43A

Figure 1. Timing Resistor versus

Oscillator Frequency

80 50

Ω

20

8.0

5.0

, TIMING RESISTOR (k )

VCC = 15 V

2.0

T

R

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

TA = 25

°

C

f

, OSCILLAT OR FREQUENCY (Hz)

OSC

Figure 3. Oscillator Discharge Current

versus T emperature

9.0

VCC = 15 V V

= 2.0 V

8.5

OSC

Figure 2. Output Deadtime versus

Oscillator Frequency

100

VCC = 15 V

50

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

TA = 25

°

C

f

, OSCILLAT OR FREQUENCY (Hz)

OSC

Figure 4. Maximum Output Duty Cycle

versus Timing Resistor

100

VCC = 15 V CT = 3.3 nF

90

80

I

TA = 25

dischg

°

C

= 7.2 mA

8.0

, DISCHARGE CURRENT (mA)

7.5

dischg

I

7.0 –55 –25 0 25 50 75 100 125

TA, AMBIENT TEMPERATURE (

°

C)

Figure 5. Error Amp Small Signal

Transient Response

VCC = 15 V

2.55 V

2.5 V

AV = –1.0 TA = 25

70

60

50

, MAXIMUM OUTPUT DUTY CYCLE (%)

max

D

40

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

I

= 9.5 mA

dischg

RT, TIMING RESISTOR (Ω)

Figure 6. Error Amp Large Signal

Transient Response

VCC = 15 V

°

C

20 mV/DIV

3.0 V

2.5 V

AV = –1.0

°

TA = 25

C

200 mV/DIV

2.45 V

4

0.5 µs/DIV

2.0 V

0.1 µs/DIV

MOTOROLA ANALOG IC DEVICE DATA

UC3842A, 43A UC2842A, 43A

Figure 7. Error Amp Open Loop Gain and

Phase versus Frequency

100

80

60

40

20

, OPEN LOOP VOL TAGE GAIN (dB)

0

VOL

A

–20

100 1.0 k 10 k 100 k 1.0 M

Gain

f, FREQUENCY (Hz)

Figure 9. Reference V oltage Change

versus Source Current

0

–4.0

–8.0

VCC = 15 V

VO = 2.0 V to 4.0 V

RL = 100 K

°

C

TA = 25

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

0

110

90

Figure 8. Current Sense Input Threshold

versus Error Amp Output Voltage

VCC = 15 V

TA = 25°C

TA = 125°C

TA = –55°C

2.0 4.0 6.0 8.0

VO, ERROR AMP OUTPUT VOLTAGE (V)

Figure 10. Reference Short Circuit Current

versus T emperature

VCC = 15 V

≤

0.1

RL

Ω

–12

–16

, REFERENCE VOLTAGE CHANGE (mV)

–20

ref

V

∆

–24

0 20 40 60 80 100 120

TA = 125°C

TA = 25°C

I

, REFERENCE SOURCE CURRENT (mA)

ref

TA = 55°C

Figure 11. Reference Load Regulation

VCC = 15 V

IO = 1.0 mA to 20 mA

°

C

TA = 25

70

, REFERENCE SHORT CIRCUIT CURRENT (mA)

50

SC

I

–55 –25 0 25 50 75 100 125

°

TA, AMBIENT TEMPERATURE (

C)

Figure 12. Reference Line Regulation

VCC = 12 V to 25 V

°

C

TA = 25

, OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)

O

V

∆

2.0 ms/DIV

MOTOROLA ANALOG IC DEVICE DATA

, OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)

O

V

∆

2.0 ms/DIV

5