Motorola UC3845N, UC3845DR2, UC3845D, UC3844N, UC3844DR2 Datasheet

     

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 deadtimes 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 (SO–14). The SO–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).

• 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 Motorola SENSEFET Products

Simplified Block Diagram

V

7(12)

CC

8(14)

RTC

4(7)

Voltage

Feedback

2(3)

1(1) Output Comp.

V

ref

R

V

R

T

Oscillator

+ –

Error

Amplifier

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

ref

Undervoltage

Lockout

Gnd 5(9)

5.0V

Reference

Latching

Flip

Flop

&

PWM

V

CC

Undervoltage

Lockout

V

C

7(11)

Output

6(10)

PWR GND

5(8)

Current Sense

3(5)

Order this document by UC3844/D

   

HIGH PERFORMANCE

CURRENT MODE

CONTROLLERS

N SUFFIX

PLASTIC PACKAGE

CASE 626

D SUFFIX

PLASTIC PACKAGE

CASE 751A

(SO–14)

PIN CONNECTIONS

Compensation

Voltage Feedback

Current Sense

Compensation

Voltage Feedback

Current Sense

ORDERING INFORMATION

Device

UC3844D UC3845D UC3844N UC3845N UC2844D UC2845D UC2844N UC2845N

1 2 3

45

RT/C

T

(T op View)

1 2

NC

3 4

NC

5 6

NC

RT/C

7

T

(T op V iew)

Operating

Temperature Range

TA = 0° to +70°C

TA = – 25° to +85°C

8

1

14

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

Package

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

MOTOROLA ANALOG IC DEVICE DATA

 Motorola, Inc. 1996 Rev 1

1

UC3844, 45 UC2844, 45

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, Case 751A

Maximum Power Dissipation @ TA = 25°C 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

P

D

R

θJA

P

D

R

θJA

J

T

A

UC2844, UC2845

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.)

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 T emperature Stability T Total Output V ariation 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 – 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

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

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 UC3844, UC3845 T

low

T

= –25°C for UC2844, UC2845 T

low

= 2.0 V, TJ = 25°C) I

osc

f

osc

47 46

osc/∆V

∆f

osc/∆T

osc

dischg

= +70°C for UC3844, UC3845

high

= +85°C for UC2844, UC2845

high

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

– 1.6 – – 1.6 – V – 10.8 – – 10.8 – mA

52

–

60

57

47 46

52

–

60

57

kHz

2

MOTOROLA ANALOG IC DEVICE DATA

UC3844, 45 UC2844, 45

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,)

UC284X UC384X

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

6.2

–

0.8

–

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 V 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

(I

Sink Sink Sink Sink

Sink

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

= 1.0 mA

V

OL

V

OH

V

OL(UVLO)

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 – 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

7.8

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

46

48

–

50

–

47

0

48

–

50

0

TOTAL DEVICE

Power Supply Current (Note 2)

Startup: (VCC = 6.5 V for UCX845A,

(VCC 14 V for UCX844) 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 UC3844, UC3845 T

low

T

= –25°C for UC2844, UC2845 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

high

I

CC

– –

Z

= +70°C for UC3844, UC3845

= +85°C for UC2844, UC2845

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

UC3844, 45 UC2844, 45

Figure 1. Timing Resistor versus

Oscillator Frequency

100

50

Ω

20

10

5.0

, TIMING RESISTOR (k )

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

, OSCILLAT OR FREQUENCY (Hz)

osc

VCC = 15 V TA = 25

Figure 3. Error Amp Small Signal

Transient Response

VCC = 15 V

2.55 V

AV = –1.0 TA = 25

Figure 2. Output Deadtime versus

Oscillator Frequency

75

°

C

70

65

60

55

% DT, PERCENT OUTPUT DEADTIME

50

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

CT = 10 nF

f

, OSCILLAT OR FREQUENCY (Hz)

osc

5.0 nF

500 pF

1.0 nF

2.0 nF

100 pF

200 pF

Figure 4. Error Amp Large Signal

Transient Response

VCC = 15 V

°

C

3.0 V

AV = –1.0

°

TA = 25

C

2.5 V

2.45 V

0.5 µs/DIV

Figure 5. 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)

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

°

C

TA = 25

Phase

10 M10

2.5 V

20 mV/DIV

2.0 V

Figure 6. Current Sense Input Threshold

0

30

60

90

120

150 180

1.2 VCC = 15 V

1.0

0.8

0.6

0.4

, EXCESS PHASE (DEGREES)

0.2

φ

, CURRENT SENSE INPUT THRESHOLD (V)

th

0

V

0

200 mV/DIV

1.0 µs/DIV

versus Error Amp Output Voltage

TA = 25°C

TA = 125°C

TA = –55°C

2.0 4.0 6.0 8.0

VO, ERROR AMP OUTPUT VOLTAGE (V)

4

MOTOROLA ANALOG IC DEVICE DATA

UC3844, 45 UC2844, 45

Figure 7. Reference V oltage Change

versus Source Current

0

VCC = 15 V

–4.0

–8.0

–12

–16

, REFERENCE VOLTAGE CHANGE (mV)

–20

ref

V

∆

–24

0 20 40 60 80 100 120

TA = 125°C

TA = –55°C

TA = 25°C

I

, REFERENCE SOURCE CURRENT (mA)

ref

Figure 9. Reference Load Regulation Figure 10. Reference Line Regulation

VCC = 15 V IO = 1.0 mA to 20 mA

°

C

TA = 25

Figure 8. Reference Short Circuit Current

versus T emperature

110

VCC = 15 V

≤

0.1

RL

90

70

, REFERENCE SHORT CIRCUIT CURRENT (mA)

50

SC

–55 –25 0 25 50 75 100 125

I

TA, AMBIENT TEMPERATURE (

°

C)

VCC = 12 V to 25 V

°

C

TA = 25

Ω

, OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)

O

V

∆

Figure 11. Output Saturation Voltage

versus Load Current

, OUTPUT SA TURATION VOLTAGE (V)

sat

V

0 –1.0 –2.0

3.0

2.0

1.0 0

V

CC

TA = 25°C

TA = –55°C

IO, OUTPUT LOAD CURRENT (mA)

2.0 ms/DIV

Source Saturation

(Load to Ground)

TA = –55°C

Sink Saturation

(Load to VCC)

VCC = 15 V

µ

s Pulsed Load

80

120 Hz Rate

TA = 25°C

Gnd

, OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)

O

V

∆

2.0 ms/DIV

Figure 12. Output Waveform

VCC = 15 V

90%

10%

8006004002000

50 ns/DIV

CL = 1.0 nF

°

C

TA = 25

MOTOROLA ANALOG IC DEVICE DATA

5