UC384XBDR2_技术文档

UC3842B, UC3843B,

UC2842B, UC2843B,

NCV3843BV

High Performance

Current Mode Controllers

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The UC3842B, UC3843B series are high performance fixed

frequency current mode controllers. They 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.

PDIP–8

N SUFFIX

CASE 626

8

1

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.

SO–8

D1 SUFFIX

CASE 751

8

1

These devices are available in an 8–pin dual–in–line and surface

mount (SO–8) 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 UCX842B has UVLO thresholds of 16 V (on) and 10 V (off),

ideally suited for off–line converters. The UCX843B is tailored for

lower voltage applications having UVLO thresholds of 8.5 V (on) and

7.6 V (off).

SO–14

D SUFFIX

CASE 751A

14

1

PIN CONNECTIONS

• Trimmed Oscillator for Precise Frequency Control

• Oscillator Frequency Guaranteed at 250 kHz

• Current Mode Operation to 500 kHz

1

2

3

4

8

7

6

5

Compensation

Voltage Feedback

Current Sense

V

ref

CC

Output

Gnd

R /C

T

• Automatic Feed Forward Compensation

• Latching PWM for Cycle–By–Cycle Current Limiting

• Internally Trimmed Reference with Undervoltage Lockout

• High Current Totem Pole Output

(Top View)

Compensation

1

2

3

4

5

6

7

14

13

12

11

10

9

V

ref

NC

Voltage Feedback

NC

V

CC

• Undervoltage Lockout with Hysteresis

C

• Low Startup and Operating Current

Current Sense

NC

Output

V

CC

7(12)

Gnd

8

R /C

T

Power Ground

T

V

CC

ref

5.0V

Reference

Undervoltage

Lockout

(Top View)

8(14)

R

V

ref

V

C

Undervoltage

Lockout

ORDERING INFORMATION

See detailed ordering and shipping information in the package

7(11)

dimensions section on page 16 of this data sheet.

R /C

T

Output

T

Oscillator

6(10)

4(7)

Latching

PWM

Power

Ground

5(8)

DEVICE MARKING INFORMATION

See general marking information in the device marking

section on page 17 of this data sheet.

Voltage

Feedback

Input

+

-

2(3)

Error

Amplifier

Current

Sense

Input

Output

Compensation

3(5)

1(1)

Gnd 5(9)

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

Figure 1. Simplified Block Diagram

Semiconductor Components Industries, LLC, 2001

1

Publication Order Number:

December, 2001 – Rev. 3

UC3842B/D

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

MAXIMUM RATINGS

Rating

Symbol

, V

Value

Unit

Bias and Driver Voltages (Zero Series Impedance, see also Total Device spec)

V

30

V

CC

C

Total Power Supply and Zener Current

Output Current, Source or Sink (Note 1)

Output Energy (Capacitive Load per Cycle)

Current Sense and Voltage Feedback Inputs

Error Amp Output Sink Current

(I + I )

30

mA

A

CC

Z

I

O

1.0

5.0

W

µJ

V

in

– 0.3 to + 5.5

10

I

O

mA

Power Dissipation and Thermal Characteristics

D Suffix, Plastic Package, SO–14 Case 751A

Maximum Power Dissipation @ T = 25°C

Thermal Resistance, Junction–to–Air

P

862

145

mW

°C/W

A

D

R

θ

JA

D1 Suffix, Plastic Package, SO–8 Case 751

Maximum Power Dissipation @ T = 25°C

Thermal Resistance, Junction–to–Air

N Suffix, Plastic Package, Case 626

P

702

178

mW

°C/W

A

D

R

θ

JA

Maximum Power Dissipation @ T = 25°C

Thermal Resistance, Junction–to–Air

P

1.25

100

W

°C/W

A

D

R

θ

JA

J

Operating Junction Temperature

T

+150

°C

Operating Ambient Temperature

UC3842B, UC3843B

T

A

0 to + 70

UC2842B, UC2843B

UC3842BV, UC3843BV, NCV3843BV

– 25 to + 85

–40 to +105

Storage Temperature Range

T

stg

– 65 to +150

°C

ELECTRICAL CHARACTERISTICS (V = 15 V [Note 2], R = 10 k, C = 3.3 nF. For typical values T = 25°C, for min/max values

CC

T

A

T is the operating ambient temperature range that applies [Note 3], unless otherwise noted.)

A

UC284XB

UC384XB, XBV

Characteristics

REFERENCE SECTION

Reference Output Voltage (I = 1.0 mA, T = 25°C)

Symbol

Min

Typ

Max

Min

Typ

Max

Unit

V

ref

4.95

–

5.0

2.0

3.0

0.2

–

5.05

20

25

–

4.9

–

5.0

2.0

3.0

0.2

–

5.1

20

V

mV

mV/°C

V

O

J

Line Regulation (V = 12 V to 25 V)

Reg

CC

line

load

S

Load Regulation (I = 1.0 mA to 20 mA)

Reg

–

25

O

Temperature Stability

T

–

Total Output Variation over Line, Load, and Temperature

Output Noise Voltage (f = 10 Hz to 10 kHz, T = 25°C)

V

ref

4.9

–

5.1

–

4.82

–

5.18

–

V

n

50

µV

J

Long Term Stability (T = 125°C for 1000 Hours)

S

–

5.0

– 85

–

5.0

– 85

–

mV

mA

A

Output Short Circuit Current

I

– 30

–180

– 30

–180

SC

OSCILLATOR SECTION

Frequency

f

kHz

OSC

T = 25°C

49

48

52

–

55

56

49

48

52

–

55

56

J

T = T

to T

high

A

low

T = 25°C (R = 6.2 k, C = 1.0 nF)

225

250

275

225

250

275

J

T

Frequency Change with Voltage (V = 12 V to 25 V)

∆f

/∆V

/∆T

–

0.2

1.0

1.6

1.0

–

0.2

0.5

1.6

1.0

–

%

CC

OSC

Frequency Change with Temperature, T = T

to T

high

A

low

OSC

Oscillator Voltage Swing (Peak–to–Peak)

V

–

V

OSC

Discharge Current (V

= 2.0 V)

I

mA

OSC

dischg

T = 25°C

7.8

7.5

–

8.3

–

8.8

–

7.8

7.6

7.2

8.3

–

8.8

J

T = T

to T

(UC284XB, UC384XB)

(UC384XBV)

A

low

high

T = T

A

1. Maximum Package power dissipation limits must be observed.

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

CC

3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.

T

= 0°C for UC3842B, UC3843B; –25°C for UC2842B, UC2843B; –40°C for UC3842BV, UC3843BV

= +70°C for UC3842B, UC3843B; +85°C for UC2842B, UC2843B; +105°C for UC3842BV, UC3843BV

low

high

NCV3843BV: T = –40°C, T

= +105°C. Guaranteed by design. NCV prefix is for automotive and other applications requiring site and

low

high

change control.

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UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

ELECTRICAL CHARACTERISTICS (V = 15 V [Note 4], R = 10 k, C = 3.3 nF. For typical values T = 25°C, for min/max values

CC

T

A

T is the operating ambient temperature range that applies [Note 5], unless otherwise noted.)

A

UC284XB

UC384XB, XBV

Characteristics

ERROR AMPLIFIER SECTION

Voltage Feedback Input (V = 2.5 V)

Symbol

Min

Typ

Max

Min

Typ

Max

Unit

V

FB

2.45

–

2.5

– 0.1

90

2.55

–1.0

–

2.42

–

2.5

– 0.1

90

2.58

V

µA

O

Input Bias Current (V = 5.0 V)

I

IB

– 2.0

FB

Open Loop Voltage Gain (V = 2.0 V to 4.0 V)

A

VOL

65

0.7

60

65

0.7

60

–

dB

O

Unity Gain Bandwidth (T = 25°C)

BW

1.0

70

–

1.0

70

MHz

dB

J

Power Supply Rejection Ratio (V = 12 V to 25 V)

PSRR

–

CC

Output Current

mA

Sink (V = 1.1 V, V = 2.7 V)

I

Sink

I

Source

2.0

– 0.5

12

–1.0

–

2.0

– 0.5

12

–1.0

–

O

FB

Source (V = 5.0 V, V = 2.3 V)

O

FB

Output Voltage Swing

V

High State (R = 15 k to ground, V = 2.3 V)

V

OH

5.0

6.2

–

5.0

6.2

–

L

FB

Low State (R = 15 k to V , V = 2.7 V)

V

OL

L

ref

FB

(UC284XB, UC384XB)

(UC384XBV)

–

0.8

–

1.1

–

0.8

1.1

1.2

CURRENT SENSE SECTION

Current Sense Input Voltage Gain (Notes 6 & 7)

(UC284XB, UC384XB)

A

V/V

V

2.85

–

3.0

–

3.15

–

2.85

3.0

3.15

3.25

(UC384XBV)

Maximum Current Sense Input Threshold (Note 6)

(UC284XB, UC384XB)

V

th

0.9

–

1.0

–

1.1

–

0.9

0.85

1.0

1.1

(UC384XBV)

Power Supply Rejection Ratio (V = 12 V to 25 V, Note 6)

PSRR

–

70

–

70

–

dB

µA

ns

CC

Input Bias Current

I

– 2.0

150

–10

300

– 2.0

150

–10

300

IB

PLH(In/Out)

Propagation Delay (Current Sense Input to Output)

t

OUTPUT SECTION

Output Voltage

V

Low State (I

(I

= 20 mA)

= 200 mA) (UC284XB, UC384XB)

(UC384XBV)

= 20 mA) (UC284XB, UC384XB)

(UC384XBV)

= 200 mA)

V

–

13

–

12

0.1

1.6

–

13.5

–

0.4

2.2

–

13

12.9

12

0.1

1.6

13.5

13.4

0.4

2.2

2.3

–

Sink

OL

High State (I

(I

V

OH

Source

13.4

–

Source

Output Voltage with UVLO Activated (V = 6.0 V, I

= 1.0 mA)

V

–

0.1

50

1.1

150

–

0.1

50

1.1

150

V

CC

Sink

OL(UVLO)

Output Voltage Rise Time (C = 1.0 nF, T = 25°C)

t

r

ns

L

J

Output Voltage Fall Time (C = 1.0 nF, T = 25°C)

t

f

L

J

UNDERVOLTAGE LOCKOUT SECTION

Startup Threshold (V

UCX842B, BV

)

V

CC

th

15

7.8

16

8.4

17

9.0

14.5

7.8

16

8.4

17.5

9.0

UCX843B, BV

Minimum Operating Voltage After Turn–On (V

UCX842B, BV

)

V

CC(min)

CC

9.0

7.0

10

7.6

11

8.2

8.5

7.0

10

7.6

11.5

8.2

UCX843B, BV

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

CC

5. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.

T

= 0°C for UC3842B, UC3843B; –25°C for UC2842B, UC2843B; –40°C for UC3842BV, UC3843BV

= +70°C for UC3842B, UC3843B; +85°C for UC2842B, UC2843B; +105°C for UC3842BV, UC3843BV

low

high

NCV3843BV: T = –40°C, T

= +125°C. Guaranteed by design. NCV prefix is for automotive and other applications requiring site and

low

high

change control.

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

FB

∆V Output Compensation

∆V Current Sense Input

7. Comparator gain is defined as: A

V

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UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

ELECTRICAL CHARACTERISTICS (V = 15 V [Note 8], R = 10 k, C = 3.3 nF, for typical values T = 25°C, for min/max values

CC

T

A

T is the operating ambient temperature range that applies [Note 9], unless otherwise noted.)

A

UC284XB

UC384XB, BV

Typ

Characteristics

Symbol

Min

Typ

Max

Min

Max

Unit

PWM SECTION

Duty Cycle

%

Maximum (UC284XB, UC384XB)

Maximum (UC384XBV)

Minimum

DC

94

–

96

–

0

94

93

–

96

–

0

(max)

DC

(min)

TOTAL DEVICE

Power Supply Current

Startup (V = 6.5 V for UCX843B,

I

+ I

mA

V

CC

C

–

0.3

0.5

–

0.3

0.5

CC

Startup (V 14 V for UCX842B, BV)

CC

Operating (Note 8)

–

12

36

17

–

12

36

17

–

Power Supply Zener Voltage (I = 25 mA)

V

Z

30

CC

8. Adjust V above the Startup threshold before setting to 15 V.

CC

9. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.

T

= 0°C for UC3842B, UC3843B; –25°C for UC2842B, UC2843B; –40°C for UC3842BV, UC3843BV

= +70°C for UC3842B, UC3843B; +85°C for UC2842B, UC2843B; +105°C for UC3842BV, UC3843BV

low

high

NCV3843BV: T = –40°C, T

= +125°C. Guaranteed by design. NCV prefix is for automotive and other applications requiring site and

low

high

change control.

80

50

100

1. C = 10 nF

T

2. C = 5.0 nF

4

50

T

3. C = 2.0 nF

3

T

4. C = 1.0 nF

2

T

5. C = 500 pF

20

10

T

6. C = 200 pF

1

T

7. C = 100 pF

T

8.0

5.0

7

6

5

5.0

V

= 15 V

2.0

0.8

CC

V

= 15 V

2.0

1.0

CC

T = 25°C

A

T = 25°C

A

10 k

20 k

50 k

100 k

200 k

500 k

1.0 M

10 k

20 k

50 k

100 k

200 k

500 k

1.0 M

f

, OSCILLATOR FREQUENCY (kHz)

f

OSC

, OSCILLATOR FREQUENCY (kHz)

OSC

Figure 2. Timing Resistor

versus Oscillator Frequency

Figure 3. Output Deadtime

versus Oscillator Frequency

9.0

8.5

8.0

7.5

7.0

100

90

80

70

60

50

40

V

= 15 V

= 2.0 V

CC

OSC

I

= 7.5 mA

dischg

I

= 8.8 mA

dischg

V

= 15 V

C = 3.3 nF

CC

T

T = 25°C

A

-Ă55

-Ă25

0

25

50

75

100

125

0.8 1.0

2.0

3.0

4.0 5.0 6.0 7.0 8.0

T , AMBIENT TEMPERATURE (°C)

A

R , TIMING RESISTOR (kΩ)

T

Figure 4. Oscillator Discharge Current

versus Temperature

Figure 5. Maximum Output Duty Cycle

versus Timing Resistor

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UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

2.55 V

2.50 V

2.45 V

V

CC

A = -1.0

T = 25°C

A

= 15 V

V

CC

A = -1.0

T = 25°C

A

= 15 V

3.0 V

V

2.5 V

2.0 V

0.5 µs/DIV

1.0 µs/DIV

Figure 6. Error Amp Small Signal

Transient Response

Figure 7. Error Amp Large Signal

Transient Response

100

80

60

40

20

1.2

0

V

= 15 V

= 2.0 V to 4.0 V

CC

V

CC

= 15 V

O

1.0

0.8

0.6

0.4

0.2

0

30

60

90

120

R = 100 K

L

T = 25°C

A

Gain

T = 25°C

A

T = 125°C

A

Phase

T = -55°C

A

0

150

180

-Ă20

10

100

1.0 k

10 k

100 k

1.0 M

10 M

0

2.0

4.0

6.0

8.0

f, FREQUENCY (Hz)

V , ERROR AMP OUTPUT VOLTAGE (V)

O

Figure 8. Error Amp Open Loop Gain and

Phase versus Frequency

Figure 9. Current Sense Input Threshold

versus Error Amp Output Voltage

0

-Ă4.0

-Ă8.0

-12

110

V

= 15 V

CC

V

= 15 V

CC

R ≤ 0.1 Ω

L

90

70

50

T = -55°C

A

T = 125°C

A

-16

-Ă20

-Ă24

T = 25°C

A

0

20

I

40

60

80

100

120

-Ă55

-Ă25

0

25

50

75

100

125

, REFERENCE SOURCE CURRENT (mA)

T , AMBIENT TEMPERATURE (°C)

ref

A

Figure 10. Reference Voltage Change

versus Source Current

Figure 11. Reference Short Circuit Current

versus Temperature

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UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

V

= 15 V

= 1.0 mA to 20 mA

CC

V

= 12 V to 25

CC

I

O

T = 25°C

A

T = 25°C

A

2.0 ms/DIV

Figure 12. Reference Load Regulation

Figure 13. Reference Line Regulation

0

-1.0

-Ă2.0

Source Saturation

(Load to Ground)

V

= 15 V

CC

V

CC

80 µs Pulsed Load

120 Hz Rate

T = 25°C

A

V

= 15 V

C = 1.0 nF

CC

90%

L

T = 25°C

A

T = -Ă55°C

A

3.0

2.0

1.0

0

T = -Ă55°C

A

T = 25°C

A

Sink Saturation

)

Gnd

600

10%

(Load to V

CC

0

200

400

800

50 ns/DIV

I , OUTPUT LOAD CURRENT (mA)

O

Figure 14. Output Saturation Voltage

versus Load Current

Figure 15. Output Waveform

25

20

15

10

5

V

= 30 V

C = 15 pF

CC

L

T = 25°C

A

R = 10 k

T

C = 3.3 nF

T

V

FB

= 0 V

I

= 0 V

Sense

T = 25°C

A

0

10

20

, SUPPLY VOLTAGE (V)

30

40

100 ns/DIV

V

CC

Figure 16. Output Cross Conduction

Figure 17. Supply Current versus Supply Voltage

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UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

PIN FUNCTION DESCRIPTION

8–Pin

14–Pin

Function

Description

1

2

1

3

Compensation

This pin is the Error Amplifier output and is made available for loop compensation.

Voltage

Feedback

This is the inverting input of the Error Amplifier. It is normally connected to the switching

power supply output through a resistor divider.

3

4

5

7

Current

Sense

A voltage proportional to inductor current is connected to this input. The PWM uses this

information to terminate the output switch conduction.

R /C

The Oscillator frequency and maximum Output duty cycle are programmed by

T

connecting resistor R to V and capacitor C to ground. Operation to 500 kHz

T

ref

T

is possible.

5

6

Gnd

This pin is the combined control circuitry and power ground.

10

Output

This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are

sourced and sunk by this pin.

7

8

12

14

8

V

This pin is the positive supply of the control IC.

CC

V

This is the reference output. It provides charging current for capacitor C through resistor R .

ref

T

Power

Ground

This pin is a separate power ground return that is connected back to the power source. It is

used to reduce the effects of switching transient noise on the control circuitry.

11

V

C

The Output high state (V ) is set by the voltage applied to this pin. With a separate

OH

power source connection, it can reduce the effects of switching transient noise on the

control circuitry.

9

Gnd

NC

This pin is the control circuitry ground return and is connected back to the power

source ground.

2,4,6,13

No connection. These pins are not internally connected.

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UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

OPERATING DESCRIPTION

The UC3842B, UC3843B series are high performance,

This occurs when the power supply is operating and the load

is removed, or at the beginning of a soft–start interval

(Figures 24, 25). The Error Amp minimum feedback

resistance is limited by the amplifier’s source current

fixed frequency, current mode controllers. They are

specifically designed for Off–Line and dc–to–dc converter

applications offering the designer a cost–effective solution

with minimal external components. A representative block

diagram is shown in Figure 18.

(0.5 mA) and the required output voltage (V ) to reach the

OH

comparator’s 1.0 V clamp level:

3.0 (1.0 V) + 1.4 V

R_f(min)

≈

= 8800 Ω

Oscillator

0.5 mA

The oscillator frequency is programmed by the values

selected for the timing components R and C . Capacitor C

T

Current Sense Comparator and PWM Latch

is charged from the 5.0 V reference through resistor R to

T

The UC3842B, UC3843B operate as a current mode

controller, whereby output switch conduction is initiated by

the oscillator and terminated when the peak inductor current

reaches the threshold level established by the Error

Amplifier Output/Compensation (Pin 1). Thus the error

approximately 2.8 V and discharged to 1.2 V by an internal

current sink. During the discharge of C , the oscillator

T

generates an internal blanking pulse that holds the center

input of the NOR gate high. This causes the Output to be in

a low state, thus producing a controlled amount of output

signal controls the peak inductor current on

a

deadtime. Figure 2 shows R versus Oscillator Frequency

T

cycle–by–cycle basis. The Current Sense Comparator PWM

Latch configuration used ensures that only a single pulse

appears at the Output during any given oscillator cycle. The

inductor current is converted to a voltage by inserting the

and Figure 3, Output Deadtime versus Frequency, both for

given values of C . Note that many values of R and C will

T

give the same oscillator frequency but only one combination

will yield a specific output deadtime at a given frequency.

The oscillator thresholds are temperature compensated to

within ±6% at 50 kHz. Also because of industry trends

moving the UC384X into higher and higher frequency

applications, the UC384XB is guaranteed to within ±10% at

250 kHz. These internal circuit refinements minimize

variations of oscillator frequency and maximum output duty

cycle. The results are shown in Figures 4 and 5.

In many noise–sensitive applications it may be desirable

to frequency–lock the converter to an external system clock.

This can be accomplished by applying a clock signal to the

circuit shown in Figure 21. For reliable locking, the

free–running oscillator frequency should be set about 10%

less than the clock frequency. A method for multi–unit

synchronization is shown in Figure 22. By tailoring the

clock waveform, accurate Output duty cycle clamping can

be achieved.

ground–referenced sense resistor R in series with the

S

source of output switch Q1. This voltage is monitored by the

Current Sense Input (Pin 3) and compared to a level derived

from the Error Amp Output. The peak inductor current under

normal operating conditions is controlled by the voltage at

pin 1 where:

V_{(Pin 1)}– 1.4 V

I_pk

=

3 R_S

Abnormal operating conditions occur when the power

supply output is overloaded or if output voltage sensing is

lost. Under these conditions, the Current Sense Comparator

threshold will be internally clamped to 1.0 V. Therefore the

maximum peak switch current is:

1.0 V

R_S

I_pk(max)

=

When designing a high power switching regulator it

becomes desirable to reduce the internal clamp voltage in

Error Amplifier

order to keep the power dissipation of R to a reasonable

A fully compensated Error Amplifier with access to the

inverting input and output is provided. It features a typical

dc voltage gain of 90 dB, and a unity gain bandwidth of

1.0 MHz with 57 degrees of phase margin (Figure 8). The

non–inverting input is internally biased at 2.5 V and is not

pinned out. The converter output voltage is typically divided

down and monitored by the inverting input. The maximum

input bias current is –2.0 µA which can cause an output

voltage error that is equal to the product of the input bias

current and the equivalent input divider source resistance.

The Error Amp Output (Pin 1) is provided for external

loop compensation (Figure 32). The output voltage is offset

by two diode drops (≈1.4 V) and divided by three before it

connects to the non–inverting input of the Current Sense

Comparator. This guarantees that no drive pulses appear at

S

level. A simple method to adjust this voltage is shown in

Figure 23. The two external diodes are used to compensate

the internal diodes, yielding a constant clamp voltage over

temperature. Erratic operation due to noise pickup can result

if there is an excessive reduction of the I

voltage.

clamp

pk(max)

A narrow spike on the leading edge of the current

waveform can usually be observed and may cause the power

supply to exhibit an instability when the output is lightly

loaded. This spike is due to the power transformer

interwinding capacitance and output rectifier recovery time.

The addition of an RC filter on the Current Sense Input with

a time constant that approximates the spike duration will

usually eliminate the instability (refer to Figure 27).

the Output (Pin 6) when pin 1 is at its lowest state (V ).

OL

http://onsemi.com

8

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

V

CC

V

in

V

CC 7(12)

36V

V

ref

Reference

Regulator

8(14)

(See

Text)

+

-

V

CC

UVLO

R

V

C

Internal

Bias

2.5V

R

C

T

7(11)

+

3.6V

V

ref

UVLO

-

Output

Q1

Oscillator

4(7)

6(10)

T

+

1.0mA

S

Power Ground

2R

Q

Voltage

Feedback

Input

PWM

Latch

R

5(8)

2(3)

1(1)

R

Error

Amplifier

1.0V

Current Sense Input

Output/

Compensation

Current Sense

Comparator

3(5)

R

S

Gnd 5(9)

Pin numbers adjacent to terminals are for the 8-pin dual-in-line package.

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

= Sink Only Positive True Logic

Figure 18. Representative Block Diagram

Capacitor C

T

Latch

Set" Input

Output/

Compensation

Current Sense

Input

Latch

Reset" Input

Output

Small R /Large C

T

Large R /Small C

T

Figure 19. Timing Diagram

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9

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

Undervoltage Lockout

Design Considerations

Two undervoltage lockout comparators have been

incorporated to guarantee that the IC is fully functional

before the output stage is enabled. The positive power

Do not attempt to construct the converter on

wire–wrap or plug–in prototype boards. High frequency

circuit layout techniques are imperative to prevent

pulse–width jitter. This is usually caused by excessive noise

pick–up imposed on the Current Sense or Voltage Feedback

inputs. Noise immunity can be improved by lowering circuit

impedances at these points. The printed circuit layout should

contain a ground plane with low–current signal and

high–current switch and output grounds returning on

separate paths back to the input filter capacitor. Ceramic

supply terminal (V ) and the reference output (V ) are

CC

ref

each monitored by separate comparators. Each has built–in

hysteresis to prevent erratic output behavior as their

respective thresholds are crossed. The V

comparator

CC

upper and lower thresholds are 16 V/10 V for the UCX842B,

and 8.4 V/7.6 V for the UCX843B. The V comparator

ref

upper and lower thresholds are 3.6 V/3.4 V. The large

hysteresis and low startup current of the UCX842B makes

it ideally suited in off–line converter applications where

efficient bootstrap startup techniques are required

(Figure 34). The UCX843B is intended for lower voltage

dc–to–dc converter applications. A 36 V zener is connected

bypass capacitors (0.1 µF) connected directly to V , V ,

CC

C

and V may be required depending upon circuit layout.

ref

This provides a low impedance path for filtering the high

frequency noise. All high current loops should be kept as

short as possible using heavy copper runs to minimize

radiated EMI. The Error Amp compensation circuitry and

the converter output voltage divider should be located close

to the IC and as far as possible from the power switch and

other noise–generating components.

Current mode converters can exhibit subharmonic

oscillations when operating at a duty cycle greater than 50%

with continuous inductor current. This instability is

independent of the regulator’s closed loop characteristics

and is caused by the simultaneous operating conditions of

fixed frequency and peak current detecting. Figure 20A

as a shunt regulator from V to ground. Its purpose is to

CC

protect the IC from excessive voltage that can occur during

system startup. The minimum operating voltage (V ) for

CC

the UCX842B is 11 V and 8.2 V for the UCX843B.

These devices contain a single totem pole output stage that

was specifically designed for direct drive of power

MOSFETs. It is capable of up to ±1.0 A peak drive current

and has a typical rise and fall time of 50 ns with a 1.0 nF load.

Additional internal circuitry has been added to keep the

Output in a sinking mode whenever an undervoltage lockout

is active. This characteristic eliminates the need for an

external pull–down resistor.

shows the phenomenon graphically. At t , switch

0

conduction begins, causing the inductor current to rise at a

The SO–14 surface mount package provides separate pins

slope of m . This slope is a function of the input voltage

1

for V (output supply) and Power Ground. Proper

divided by the inductance. At t , the Current Sense Input

C

1

implementation will significantly reduce the level of

switching transient noise imposed on the control circuitry.

reaches the threshold established by the control voltage.

This causes the switch to turn off and the current to decay at

This becomes particularly useful when reducing the I

a slope of m , until the next oscillator cycle. The unstable

pk(max)

2

clamp level. The separate V supply input allows the

designer added flexibility in tailoring the drive voltage

condition can be shown if a perturbation is added to the

control voltage, resulting in a small ∆I (dashed line). With

a fixed oscillator period, the current decay time is reduced,

C

independent of V . A zener clamp is typically connected

CC

to this input when driving power MOSFETs in systems

and the minimum current at switch turn–on (t ) is increased

2

where V is greater than 20 V. Figure 26 shows proper

by∆I + ∆I m /m . The minimum current at the next cycle (t )

2 1 3

CC

power and control ground connections in a current–sensing

power MOSFET application.

decreases to (∆I + ∆I m /m ) (m /m ). This perturbation is

2 1 2 1

multiplied by m /m on each succeeding cycle, alternately

2

1

increasing and decreasing the inductor current at switch

turn–on. Several oscillator cycles may be required before

the inductor current reaches zero causing the process to

Reference

The 5.0 V bandgap reference is trimmed to ±1.0%

tolerance at T = 25°C on the UC284XB, and ±2.0% on the

UC384XB. Its primary purpose is to supply charging current

to the oscillator timing capacitor. The reference has short–

circuit protection and is capable of providing in excess of

20 mA for powering additional control system circuitry.

J

commence again. If m /m is greater than 1, the converter

2

1

will be unstable. Figure 20B shows that by adding an

artificial ramp that is synchronized with the PWM clock to

the control voltage, the ∆I perturbation will decrease to zero

on succeeding cycles. This compensating ramp (m ) must

3

have a slope equal to or slightly greater than m /2 for

2

stability. With m /2 slope compensation, the average

2

inductor current follows the control voltage, yielding true

current mode operation. The compensating ramp can be

derived from the oscillator and added to either the Voltage

Feedback or Current Sense inputs (Figure 33).

http://onsemi.com

10

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

(A)

∆I

Control Voltage

m

2

m

1

Inductor

Current

m

2

1

Dl ) Dl

V

m

2

1

2

1

ref

Dl ) Dl ĂĂĂ

8(14)

R

Oscillator Period

Bias

R

T

t

0

t

1

t

2

t

3

(B)

External

Sync

Input

Osc

4(7)

C

T

Control Voltage

+

m

3

0.01

2R

∆I

R

2(3)

1(1)

EA

47

m

1

m

2

Inductor

Current

5(9)

Oscillator Period

The diode clamp is required if the Sync amplitude is large enough to cause the bottom

side of C to go more than 300 mV below ground.

T

t

4

t

5

t

6

Figure 20. Continuous Current Waveforms

Figure 21. External Clock Synchronization

V

in

CC

7(12)

5.0V Ref

8(14)

R

+

-

Bias

8(14)

R

A

B

7(11)

6(10)

Bias

+

-

R

8

4

Q1

Osc

5.0k

3

7

6

4(7)

V

+

Clamp

1.0V

Osc

R

S

2

S

R

4(7)

1.0 mA

2R

+

5

2

Q

5(8)

3(5)

2R

EA

2(3)

1(1)

R

Comp/Latch

R

2(3)

1(1)

EA

C

MC1455

R

S

1

R

1

5(9)

1.67

R R

Where: 0 ≤ V

≤ 1.0 V

1

2

-3

+ 0.33x10

Clamp

5(9)

ǒ

Ǔ

) R

2

V

≈

Clamp

To Additional

UCX84XBs

R

1

R

2

1

ǒ

_{) 1}Ǔ

V

Clamp

1.44

(R Ă )Ă 2R )C

R

B

fĂ +Ă

D

Ă+Ă

I

Ă [Ă

(max)

pk(max)

R

Ă)Ă 2R

R

S

A

B

A

B

Figure 22. External Duty Cycle Clamp and

Multi–Unit Synchronization

Figure 23. Adjustable Reduction of Clamp Level

http://onsemi.com

11

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

V

in

CC

7(12)

5.0V Ref

8(14)

R

+

-

Bias

5.0V Ref

R

7(11)

6(10)

+

-

8(14)

R

Q1

Bias

Osc

4(7)

V

+

Clamp

+

S

R

-

1.0 mA

2R

Q

Osc

5(8)

3(5)

4(7)

2(3)

EA

2(3)

1(1)

R

+

Comp/Latch

1.0V

5(9)

R

2

S

R

1.0mA

Q

R

S

2R

R

1

C

MPSA63

1.0V

EA

1.0M

1.67

Where: 0 ≤ V

≤ 1.0 V

V

Ă[Ă

Clamp

R

2

ǒ

_{) 1}Ǔ

1(1)

_{+ * In}ƪ¹_{1 *Ă}

ƫ_ĂC

C

V

Clamp

V

R ĂR

1 2

C

5(9)

t

I

Ă [Ă

SoftĆStart

pk(max)

t

≈ 3600C in µF

Soft-Start

3ĂV

R

Ă)Ă R

R

S

Clamp

1

2

Figure 24. Soft–Start Circuit

Figure 25. Adjustable Buffered Reduction of

Clamp Level with Soft–Start

V

in

CC

R

I

r

S pk DS(on)

) R

V

in

V

[

CC

(12)

Pin 5

r

DM(on)

S

If: SENSEFET = MTP10N10M

= 200

7(12)

R

S

5.0V Ref

Then :Ă V Ă [Ă 0.075ĂI

PinĂ5 pk

+

-

5.0V Ref

+

-

D

SENSEFET

(11)

(10)

+

-

7(11)

S

K

+

-

G

Q1

M

6(10)

5(8)

S

R

Q

S

R

(8)

(5)

Q

Comp/Latch

Power Ground:

To Input Source

Return

3(5)

R

Comp/Latch

R

1/4 W

S

C

R

S

Control Circuitry Ground:

To Pin (9)

Virtually lossless current sensing can be achieved with the implementation of a

SENSEFET power switch. For proper operation during over-current conditions,

reduction of the I clamp level must be implemented. Refer to Figures 23 and 25.

a

The addition of the RC filter will eliminate instability caused by the leading

edge spike on the current waveform.

pk(max)

Figure 26. Current Sensing Power MOSFET

Figure 27. Current Waveform Spike Suppression

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12

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

V

in

CC

I

B

7(12)

V

in

+

0

5.0V Ref

Base Charge

Removal

+

-

7(11)

+

-

C1

R

g

Q1

6(10)

S

R

Q

5(8)

3(5)

5(8)

3(5)

Comp/Latch

R

S

R

S

Series gate resistor R will damp any high frequency parasitic oscillations

g

The totem pole output can furnish negative base current for enhanced

transistor turn-off, with the addition of capacitor C .

1

caused by the MOSFET input capacitance and any series wiring inductance in

the gate-source circuit.

Figure 28. MOSFET Parasitic Oscillations

Figure 29. Bipolar Transistor Drive

V

in

V

CC

8(14)

R

Bias

7(12)

R

Isolation

Boundary

5.0V Ref

Osc

4(7)

+

-

+

V

Waveforms

+

GS

1.0 mA

2R

+

0

-

7(11)

Q1

+

-

R

EA

2(3)

1(1)

0

-

50% DC

25% DC

6(10)

5(8)

S

R

MCR

101

2N

3905

V

* 1.4

(Pin1)

3ĂR

N

S

N

5(9)

Q

_Ăǒ Ǔ

I k +

p

S

p

2N

3903

R

3(5)

Comp/Latch

C

R

N

S

N

P

The MCR101 SCR must be selected for a holding of < 0.5 mA @ T

. The simple two

A(min)

transistor circuit can be used in place of the SCR as shown. All resistors are 10 k.

Figure 30. Isolated MOSFET Drive

Figure 31. Latched Shutdown

http://onsemi.com

13

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

From V

O

2.5V

+

1.0mA

R

2R

i

2(3)

EA

R

C

f

R

f

R

d

1(1)

R ≥ 8.8 k

f

5(9)

Error Amp compensation circuit for stabilizing any current mode topology except for boost and flyback

converters operating with continuous inductor current.

From V

2.5V

O

+

1.0mA

R

p

2R

R

2(3)

i

R

EA

C

f

R

f

p

R

d

1(1)

5(9)

Error Amp compensation circuit for stabilizing current mode boost and flyback

topologies operating with continuous inductor current.

Figure 32. Error Amplifier Compensation

V

CC

V

in

7(12)

36V

5.0V Ref

+

-

8(14)

R

T

Bias

MPS3904

+

-

7(11)

6(10)

Osc

R

Slope

From V

4(7)

2(3)

O

C

T

+

-m

S

R

1.0mA

R

i

2R

Q

5(8)

3(5)

EA

R

C

1.0V

f

Comp/Latch

R

f

d

m

R

S

1(1)

- 3.0m

5(9)

The buffered oscillator ramp can be resistively summed with either the voltage

feedback or current sense inputs to provide slope compensation.

Figure 33. Slope Compensation

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14

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

L1

MBR1635

5.0V/4.0A

4.7Ω

+

T1

4.7k

+

250

MDA

202

3300

pF

2200

1000

56k

115 Vac

5.0V RTN

12V/0.3A

MUR110

1000

1N4935 1N4935

L2

10

+

7(12)

68

+

47

±12V RTN

100

1000

10

L3

1N4937

5.0V Ref

-12V/0.3A

0.01

8(14)

10k

R

+

-

MUR110

680pF

Bias

7(11)

+

-

1N4937

2.7k

22

Osc

4(7)

2(3)

MTP

4N50

4700pF

6(10)

+

1N5819

S

R

18k

L1 - 15 µH at 5.0 A, Coilcraft Z7156

L2, L3 - 25 µH at 5.0 A, Coilcraft Z7157

Q

5(8)

3(5)

EA

100

pF

150k

1(1)

1.0k

Comp/Latch

4.7k

T1 - Primary: 45 Turns #26 AWG

Secondary ±12 V: 9 Turns #30 AWG

(2 Strands) Bifiliar Wound

0.5

470pF

5(9)

Secondary 5.0 V: 4 Turns (six strands)

#26 Hexfiliar Wound

Secondary Feedback: 10 Turns

#30 AWG (2 strands) Bifiliar Wound

Core: Ferroxcube EC35-3C8

Bobbin: Ferroxcube EC35PCB1

Gap: ≈ 0.10" for a primary inductance

of 1.0 mH

Figure 34. 27 W Off–Line Flyback Regulator

Test

Conditions

Results

Line Regulation: 5.0 V

V

in

= 95 to 130 Vac

∆ = 50 mV or ± 0.5%

∆ = 24 mV or ± 0.1%

±12V

Load Regulation: 5.0 V

V

= 115 Vac,

∆ = 300 mV or ± 3.0%

∆ = 60 mV or ± 0.25%

in

I

= 1.0 A to 4.0 A

out

±12V

= 115 Vac,

in

I

= 100 mA to 300 mA

out

Output Ripple:

Efficiency

5.0 V

±12V

V

= 115 Vac

40 mV

80 mV

in

pp

V

in

= 115 Vac

70%

All outputs are at nominal load currents, unless otherwise noted

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15

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

ORDERING INFORMATION

Operating

Temperature Range

Device

Package

SO–14

SO–8

Shipping

55 Units/Rail

UC384XBD

UC384XBDR2

UC384XBD1

UC384XBD1R2

UC384XBN

2500 Tape & Reel

98 Units/Rail

T = 0° to +70°C

A

SO–8

2500 Tape & Reel

50 Units/Rail

PDIP–8

SO–14

SO–8

UC3842BN1

UC284XBD

50 Units/Rail

55 Units/Rail

UC2843BDR2

UC284XBD1

UC284XBD1R2

UC284XBN

2500 Tape & Reel

98 Units/Rail

T = –25° to +85°C

A

SO–8

2500 Tape & Reel

50 Units/Rail

PDIP–8

SO–14

SO–8

UC3843BVD

UC384XBVDR2

UC384XBVD1

55 Units/Rail

2500 Tape & Reel

98 Units/Rail

T = –40° to +105°C

A

UC384XBVD1R2

UC3843BVN

SO–8

2500 Tape & Reel

50 Units/Rail

PDIP–8

SO–14

NCV3843BVDR2

2500 Tape & Reel

X indicates either a 2 or 3 to define specific device part numbers.

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16

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

MARKING DIAGRAMS

PDIP–8

N SUFFIX

CASE 626

8

UC384xBN

UC3843BVN

AWL

UC284xBN

FAWL

AWL

YYWW

1

SO–8

D1 SUFFIX

CASE 751

8

1

384xB

ALYW

384xB

284xB

ALYW

ALYWV

1

SO–14

D SUFFIX

CASE 751A

14

1

14

1

14

*

UC384xBD

AWLYWW

UC384xBVD

AWLYWW

UC284xBD

AWLYWW

1

x

A

= 2 or 3

= Assembly Location

WL, L = Wafer Lot

YY, Y = Year

WW, W = Work Week

*This marking diagram also applies to NCV3843BV.

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17

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

PACKAGE DIMENSIONS

PDIP–8

N SUFFIX

CASE 626–05

ISSUE L

NOTES:

1. DIMENSION L TO CENTER OF LEAD WHEN

FORMED PARALLEL.

2. PACKAGE CONTOUR OPTIONAL (ROUND OR

SQUARE CORNERS).

8

5

3. DIMENSIONING AND TOLERANCING PER ANSI

Y14.5M, 1982.

–B–

MILLIMETERS

INCHES

1

4

DIM MIN

MAX

10.16

6.60 0.240

4.45 0.155

0.51 0.015

1.78 0.040

MIN

0.370

MAX

0.400

0.260

0.175

0.020

0.070

A

B

C

D

F

9.40

6.10

3.94

0.38

1.02

F

–A–

NOTE 2

L

G

H

J

2.54 BSC

0.100 BSC

0.76

0.20

2.92

1.27 0.030

0.30 0.008

3.43

0.050

0.012

0.135

K

L

0.115

C

7.62 BSC

0.300 BSC

M

N

---

0.76

10

---

1.01 0.030

10

0.040

_

J

–T–

SEATING

PLANE

N

M

D

K

G

H

M

0.13 (0.005)

T

A

B

SO–8

D1 SUFFIX

CASE 751–07

ISSUE W

–X–

NOTES:

1. DIMENSIONING AND TOLERANCING PER ANSI

Y14.5M, 1982.

A

2. CONTROLLING DIMENSION: MILLIMETER.

3. DIMENSION A AND B DO NOT INCLUDE MOLD

PROTRUSION.

8

5

4. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER

SIDE.

S

M

B

0.25 (0.010)

Y

5. DIMENSION D DOES NOT INCLUDE DAMBAR

PROTRUSION. ALLOWABLE DAMBAR

PROTRUSION SHALL BE 0.127 (0.005) TOTAL IN

EXCESS OF THE D DIMENSION AT MAXIMUM

MATERIAL CONDITION.

1

4

K

–Y–

G

MILLIMETERS

INCHES

DIM MIN

MAX

5.00

4.00

1.75

0.51

MIN

MAX

0.197

0.157

0.069

0.020

A

B

C

D

G

H

J

4.80

3.80

1.35

0.33

0.189

0.150

0.053

0.013

0.050 BSC

0.004

C

N X 45

_

SEATING

PLANE

–Z–

1.27 BSC

0.10 (0.004)

0.10

0.19

0.40

0

0.25

1.27

8

0.010

0.050

8

0.007

0.016

0

M

J

H

D

K

M

N

S

_

0.25

5.80

0.50

6.20

0.010

0.228

0.020

0.244

M

S

X

0.25 (0.010)

Z

Y

http://onsemi.com

18

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

PACKAGE DIMENSIONS

SO–14

D SUFFIX

CASE 751A–03

ISSUE F

NOTES:

1. DIMENSIONING AND TOLERANCING PER ANSI

Y14.5M, 1982.

2. CONTROLLING DIMENSION: MILLIMETER.

3. DIMENSIONS A AND B DO NOT INCLUDE

MOLD PROTRUSION.

–A–

14

1

8

7

4. MAXIMUM MOLD PROTRUSION 0.15 (0.006)

PER SIDE.

–B–

5. DIMENSION D DOES NOT INCLUDE DAMBAR

PROTRUSION. ALLOWABLE DAMBAR

PROTRUSION SHALL BE 0.127 (0.005) TOTAL

IN EXCESS OF THE D DIMENSION AT

MAXIMUM MATERIAL CONDITION.

P 7 PL

M

B

0.25 (0.010)

MILLIMETERS

DIM MIN MAX

INCHES

G

MIN

MAX

0.344

0.157

0.068

0.019

0.049

F

R X 45

_

C

A

B

C

D

F

8.55

3.80

1.35

0.35

0.40

8.75 0.337

4.00 0.150

1.75 0.054

0.49 0.014

1.25 0.016

–T–

SEATING

PLANE

J

M

G

J

1.27 BSC

0.050 BSC

K

D 14 PL

0.19

0.10

0

0.25 0.008

0.25 0.004

0.009

7

0.244

0.019

M

S

0.25 (0.010)

T

B

A

K

M

P

R

7

0

_

5.80

0.25

6.20 0.228

0.50 0.010

http://onsemi.com

19

UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV

SENSEFET is a trademark of Semiconductor Components Industries, LLC.

ON Semiconductor and

are trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes

without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular

purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability,

including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or

specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be

validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others.

SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications

intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or

death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold

SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable

attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim

alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer.

PUBLICATION ORDERING INFORMATION

Literature Fulfillment:

JAPAN: ON Semiconductor, Japan Customer Focus Center

4–32–1 Nishi–Gotanda, Shinagawa–ku, Tokyo, Japan 141–0031

Phone: 81–3–5740–2700

Literature Distribution Center for ON Semiconductor

P.O. Box 5163, Denver, Colorado 80217 USA

Phone: 303–675–2175 or 800–344–3860 Toll Free USA/Canada

Fax: 303–675–2176 or 800–344–3867 Toll Free USA/Canada

Email: ONlit@hibbertco.com

Email: r14525@onsemi.com

ON Semiconductor Website: http://onsemi.com

For additional information, please contact your local

Sales Representative.

N. American Technical Support: 800–282–9855 Toll Free USA/Canada

UC3842B/D

http://onsemi.com

20


型号：	UC384XBDR2
厂家：	ONSEMI
描述：	HIGH PERFORMANCE CURRENT MODE CONTROLLERS 高性能电流模式控制器控制器
文件：	总20页 (文件大小：295K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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