ON UC2844DG, UC2844N, UC2845DG, UC2845N, UC3844 Schematic

UC3844, UC3845, UC2844, UC2845

High Performance Current Mode Controllers

The UC3844, UC3845 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 an oscillator, 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, a latch for single pulse metering, and a flip−flop which blanks the output off every other oscillator cycle, allowing output dead times to be programmed for 50% to 70%.

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

The UCX844 has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off−line converters. The UCX845 is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and

7.6 V (off).

Features

• Current Mode Operation to 500 kHz Output Switching Frequency

• Output Deadtime Adjustable from 50% to 70%

• Automatic Feed Forward Compensation

• Latching PWM for Cycle−By−Cycle Current Limiting

• Internally Trimmed Reference with Undervoltage Lockout

• High Current Totem Pole Output

• Input Undervoltage Lockout with Hysteresis

• Low Startup and Operating Current

• Direct Interface with ON Semiconductor SENSEFETt Products

• Pb−Free Packages are Available

V

7(12)

CC

8(14)

R

TCT

4(7)

Voltage

Feedback

2(3)

1(1) Output Comp.

V

ref

R

Oscillator

+

−

Error

Amplifier

Pin numbers in parenthesis are for the D suffix SOIC−14 package.

V

Undervoltage

Lockout

GND 5(9)

5.0V

Reference

ref

Flip

Flop

&

Latching

PWM

Figure 1. Simplified Block Diagram

V

CC

Undervoltage

Lockout

V

C

7(11)

Output

6(10)

PWR GND

5(8)

Current Sense

3(5)

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PDIP−8

N SUFFIX

8

1

14

1

8

1

CASE 626

SOIC−14

D SUFFIX

CASE 751A

SOIC−8

D1 SUFFIX

CASE 751A

PIN CONNECTIONS

Compensation

Voltage Feedback

Current Sense

R

T/CT

Compensation

NC

Voltage Feedback

NC

Current Sense

NC

R

T/CT

1

2

3

45

(Top View)

1

2

3

4

5

6

7

(Top View)

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

ORDERING INFORMATION

See detailed ordering and shipping information in the package dimensions section on page 14 of this data sheet.

DEVICE MARKING INFORMATION

See general marking information in the device marking section on page page 14 of this data sheet.

July, 2006 − Rev. 7

1 Publication Order Number:

UC3844/D

UC3844, UC3845, UC2844, UC2845

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

Current Sense and Voltage Feedback Inputs V

Error Amp Output Sink Current I

in

O

Power Dissipation and Thermal Characteristics

D Suffix, Plastic Package, Case 751A

Maximum Power Dissipation @ T Thermal Resistance Junction−to−Air

N Suffix, Plastic Package, Case 626

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

Operating Junction Temperature T

Operating Ambient Temperature

UC3844, UC3845

= 25°C

A

P

D

R

q

JA

P

D

R

q

JA

J

T

A

UC2844, UC2845

Storage Temperature Range T

stg

Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability.

1. Maximum Package power dissipation limits must be observed.

1.0 A

mJ

− 0.3 to + 5.5 V

10 mA

862 145

1.25 100

mW

°C/W

W

°C/W

+ 150 °C

°C

0 to + 70

− 25 to + 85

− 65 to + 150 °C

ELECTRICAL CHARACTERISTICS (V

= 15 V, (Note 2), RT = 10 k, CT = 3.3 nF, TA = T

CC

low

to T

(Note 3), unless otherwise noted.)

high

UC284X UC384X

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

Temperature Stability T

Total Output Variation over Line, Load, Temperature V

Output Noise Voltage (f = 10 Hz to 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 −

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

= 25°C

T

J

= T

T

to T

A

low

high

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

Frequency Change with Temperature

= T

T

to T

A

low

high

Oscillator Voltage Swing (Peak−to−Peak) V

Discharge Current (V

= 2.0 V, TJ = 25°C) I

osc

Df

f

osc

osc/DV

osc/DT

osc

dischg

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

− 10.8 − − 10.8 − mA

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

65 90 − 65 90 − dB

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 UC3844, UC3845 T

T

low

−25°C for UC2844, UC2845 +85°C for UC2844, UC2845

= +70°C for UC3844, UC3845

high

mV

kHz

mA

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2

UC3844, UC3845, UC2844, UC2845

ELECTRICAL CHARACTERISTICS (V

= 15 V, (Note 4), RT = 10 k, CT = 3.3 nF, TA = T

CC

low

to T

(Note 5), unless otherwise noted.)

high

UC284X UC384X

Characteristics Symbol Min Typ Max Min Ty p Max Unit

ERROR AMPLIFIER SECTION (continued)

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

O

Source (V

= 1.1 V, VFB = 2.7 V)

= 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

5.0−6.2

0.8

1.1

−

5.0

6.2

−

0.8

−

1.1

CURRENT SENSE SECTION

Current Sense Input Voltage Gain (Notes 6 & 7)

Maximum Current Sense Input Threshold (Note 6) V

Power Supply Rejection Ratio

= 12 V to 25 V (Note 6)

V

CC

PSRR

Input Bias Current I

Propagation Delay (Current Sense Input to Output) t

PLH(IN/OUT)

A

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

− 150 300 − 150 300 ns

OUTPUT SECTION

Output Voltage

Low State (I

High State (I

Output Voltage with UVLO Activated

= 6.0 V, I

V

CC

Sink

(I

Sink

(I

Sink

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

= 1.0 mA

V

OL(UVLO)

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

r

f

−

12 12

0.1

−

1.6

13.5

13.4

0.4

2.2

−

0.1

−

13

−

12

1.6

13.5

13.4

0.4

2.2

−

− 0.1 1.1 − 0.1 1.1

− 50 150 − 50 150 ns

UNDERVOLTAGE LOCKOUT SECTION

Startup Threshold

UCX844 UCX845

Minimum Operating Voltage After Turn−On

UCX844 UCX845

V

CC(min)

th

15

7.8168.4

9.0

7.0107.6

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 DC

max

min

46

48

−

50

−

47

0

48

−

50

−

0

TOTAL DEVICE

Power Supply Current (Note 4)

I

CC

Startup:

= 6.5 V for UCX845A,

(V

CC

14 V for UCX844) Operating

(V

CC

Power Supply Zener Voltage (ICC = 25 mA) V

Z

−

0.5

−

12

1.0 17

−

0.5

−

12

1.0 17

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 UC3844, UC3845 T

T

low

−25°C for UC2844, UC2845 +85°C for UC2844, UC2845

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

7. Comparator gain is defined as: A

DV Output Compensation

V

DV Current Sense Input

= +70°C for UC3844, UC3845

high

= 0 V.

FB

mA

V

dB

mA

V

%

mA

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3

UC3844, UC3845, UC2844, UC2845

10

0

50

VCC = 15 V T

A

Ω, TIMING RESISTOR (k )

20

10

5.0

T

2.0

R

NOTE: Output switches at one−half the oscillator frequency.

1.0 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

VCC = 15 V A

= −1.0

2.55 V

V

T

A

= 25°C

75

70

65

CT = 10 nF

5.0 nF

2.0 nF

60

55

% DT, PERCENT OUTPUT DEADTIME

50

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

f

, OSCILLATOR FREQUENCY (Hz)

osc

500 pF

Figure 3. Output Deadtime versus

Oscillator Frequency

VCC = 15 V A

= −1.0

3.0 V

V

T

A

= 25°C

200 pF

1.0 nF

100 pF

2.5 V

2.45 V

100

80

60

40

20

, OPEN LOOP VOLTAGE GAIN (dB)

0

VOL

A

−20

0.5 ms/DIV

Figure 4. Error Amp Small Signal

Transient Response

VCC = 15 V V

= 2.0 V to 4.0 V

O

R

= 100 K

Gain

100 1.0 k 10 k 100 k 1.0 M

f, FREQUENCY (Hz)

L

T

= 25°C

A

Phase

2.5 V

20 mV/DIV

2.0 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

V

1.0 ms/DIV

Figure 5. Error Amp Large Signal

Transient Response

VCC = 15 V

TA = 25°C

TA = 125°C

TA = −55°C

0

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

V

O

200 mV/DIV

Figure 6. Error Amp Open Loop Gain and

Phase versus Frequency

Figure 7. Current Sense Input Threshold

versus Error Amp Output Voltage

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4

UC3844, UC3845, UC2844, UC2845

0

VCC = 15 V

−4.0

−8.0

−12

−16

−20

ref

V Δ , REFERENCE VOLTAGE CHANGE (mV)

−24 0 20 40 60 80 100 120

TA = 125°C

TA = −55°C

TA = 25°C

, REFERENCE SOURCE CURRENT (mA)

I

ref

Figure 8. Reference Voltage Change

versus Source Current

VCC = 15 V I

= 1.0 mA to 20 mA

O

TA = 25°C

110

VCC = 15 V

≤ 0.1 W

R

L

90

70

50

SC

−55 −25 0 25 50 75 100 125

, REFERENCE SHORT CIRCUIT CURRENT (mA)

, AMBIENT TEMPERATURE (°C)

I

T

A

Figure 9. Reference Short Circuit Current

versus Temperature

VCC = 12 V to 25 V T

= 25°C

A

O

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

Figure 10. Reference Load Regulation Figure 11. Reference Line Regulation

0

−1.0

−2.0

3.0

2.0

, OUTPUT SATURATION VOLTAGE (V)

1.0

sat

V

0

V

CC

TA = 25°C

TA = −55°C

Figure 12. Output Saturation Voltage

2.0 ms/DIV

Source Saturation

(Load to Ground)

TA = −55°C

Sink Saturation

(Load to V

I

, OUTPUT LOAD CURRENT (mA)

O

)

CC

versus Load Current

VCC = 15 V

80 ms Pulsed Load

120 Hz Rate

TA = 25°C

GN

D

O

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

2.0 ms/DIV

VCC = 15 V C

= 1.0 nF

90%

L

T

A

= 25°C

10%

8006004002000

50 ns/DIV

Figure 13. Output Waveform

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5

UC3844, UC3845, UC2844, UC2845

VCC = 30 V

25

C

= 15 pF

, OUTPUT VOLTAGE

CC

V

, SUPPLY CURRENT

CC

I

100 ns/DIV

L

= 255C

T

A

, SUPPLY CURRENT (mA)

CC

I

100 mA/DIV 20 V/DIV

20

15

10

5

UCX845

0

010203040

UCX844

, SUPPLY VOLTAGE (V)

V

CC

RT = 10 k C

= 3.3 nF

T

= 0 V

V

FB

I

= 0 V

Sense

T

= 255C

A

Figure 14. Output Cross Conduction Figure 15. Supply Current versus

Supply Voltage

PIN FUNCTION DESCRIPTION

8−Pin 14−Pin

1 1 Compensation This pin is Error Amplifier output and is made available for loop compensation.

2 3 Voltage

3 5 Current Sense A voltage proportional to inductor current is connected to this input. The PWM uses this

4 7 RT/C

5 − GND This pin is combined control circuitry and power ground (8−pin package only).

6 10 Output This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are

7 12 V

8 14 V

− 8 Power Ground This pin is a separate power ground return (14−pin package only) that is connected back to

− 11 V

− 9 GND This pin is the control circuitry ground return (14−pin package only) and is connected to back

− 2,4,6,13 NC No connection (14−pin package only). These pins are not internally connected.

Function Description

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

Feedback

power supply output through a resistor divider.

information to terminate the output switch conduction.

T

The Oscillator frequency and maximum Output duty cycle are programmed by connecting resistor RT to V

and capacitor CT to ground. Operation to 1.0 MHz is possible.

ref

sourced and sunk by this pin. The output switches at one−half the oscillator frequency.

CC

ref

This pin is the positive supply of the control IC.

This is the reference output. It provides charging current for capacitor CT through resistor RT.

the power source. It is used to reduce the effects of switching transient noise on the control circuitry.

C

The Output high state (VOH) is set by the voltage applied to this pin (14−pin package only). With a separate power source connection, it can reduce the effects of switching transient noise on the control circuitry.

to the power source ground.

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ON UC2844DG, UC2844N, UC2845DG, UC2845N, UC3844 Schematic [ru]