Microsemi UC3845AM, UC3845ADM, UC3844AM, UC3844ADM, UC3845AD Datasheet

DESCRIPTION KEY FEATURES

■■

■■

■ LOW START-UP CURRENT. (0.5mA max.)

■■

■■

■ TRIMMED OSCILLATOR DISCHARGE

CURRENT. (See Product Highlight)

p OPTIMIZED FOR OFF-LINE AND DC-TO-DC

CONVERTERS.

p AUTOMATIC FEED FORWARD

COMPENSATION.

p PULSE-BY-PULSE CURRENT LIMITING.
p ENHANCED LOAD RESPONSE

CHARACTERISTICS.

p UNDER-VOLTAGE LOCKOUT WITH

HYSTERESIS.

p DOUBLE PULSE SUPPRESSION.
p HIGH-CURRENT TOTEM POLE OUTPUT.

p INTERNALLY TRIMMED BANDGAP

REFERENCE.

p 500KHz OPERATION.

p LOW R

O

ERROR AMPLIFIER.

The UC184xA family of control ICs
provides all the necessary features to
implement off-line fixed-frequency,
current-mode switching power supplies
with a minimum of external compo­nents. The current mode architecture
demonstrates improved load regulation,
pulse-by-pulse current limiting and
inherent protection of the power supply
output switch. The IC includes: A
bandgap reference trimmed to ±1%
accuracy, an error amplifier, a current
sense comparator with internal clamp to
1V, a high current totem pole output
stage for fast switching of power

MOSFET's, and an externally program­mable oscillator to set frequency and
maximum duty cycle. The under­voltage lock-out is designed to operate
with 250µA typ. start-up current,
allowing an efficient bootstrap supply
voltage design. Available options for
this family of products, such as start-up
voltage hysteresis and duty cycle, are
summarized below in the Available
Options section. The UC184xA family
of control ICs is also available in 14-pin
SOIC package which makes the Power
Output Stage Collector and Ground pins
available.

APPLICATIONS

■■

■■

■ ECONOMICAL OFF-LINE FLYBACK OR

FORWARD CONVERTERS.

■ DC-DC BUCK OR BOOST CONVERTERS.

■ LOW COST DC MOTOR CONTROL.

A VAILABLE OPTIONS

Part # Start-Up Hysteresis Max. Duty

Voltage Cycle

PACKAGE ORDER INFORMATION

T

A

(°C)

Plastic DIP
8-pin

0 to 70 UC384xAM UC384xADM UC384xAD —

-40 to 85 UC284xAM UC284xADM UC284xAD UC284xAY

-55 to 125 — — — UC184xAY

M

Plastic SOIC
8-pin

DM

Plastic SOIC
14-pin

D

Ceramic DIP
8-pin

Y

Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number. (i.e. UC3842ADMT)

UCx842A 16V 6V <100%

UCx843A 8.4V 0.8V <100%

UCx844A 16V 6V <50%

UCx845A 8.4V 0.8V <50%

PRODUCT HIGHLIGHT

COMPARISON OF UC384XA VS. SG384X DISCHARGE CURRENT

UC384xA

7.5 8.3 9.3
Mean

SG384x

Min. Limit

7.8

−3σ

8.8

+3σ

SG384x

Max. Limit

Discharge Current Distribution - mA

T

A

=25°C

C URRENT MODE PWM CONTROLLER

P RODUCTION DATA SHEET

THE INFINITE POWER OF INNOVATION

Copyright © 1995
Rev. 1.2 12/95

FOR FURTHER INFORMATION CALL [phone]

11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841

UC184xA/284xA/384xA

LIN DOC #:

1840

1

C URRENT MODE PWM CONTROLLER

UC184xA/284xA/384xA

PRODUCT DATABOOK 1996/1997

Copyright © 1995

Rev. 1.2 12/95

2

P

RODUCTION DATA SHEET

ABSOLUTE MAXIMUM RATINGS (Note 1)

Supply Voltage (Low Impedance Source) (VCC) ......................................................... 30V

Supply Voltage (I

CC

< 30mA).......................................................................... Self Limiting

Output Current ............................................................................................................. ±1A

Output Energy (Capacitive Load)................................................................................. 5µJ

Analog Inputs (V

FB

& I

SENSE

) ........................................................................ -0.3V to +6.3V

Error Amp Output Sink Current ............................................................................... 10mA

Power Dissipation at T

A

= 25°C (M Package) .............................................................. 1W

Storage Temperature Range .................................................................... -65°C to +150°C

Lead Temperature (Soldering, 10 Seconds) ............................................................. 300°C

PACKAGE PIN OUTS

Note 1. Exceeding these ratings could cause damage to the device. All voltages are with respect

to Ground. Currents are positive into, negative out of the specified terminal. Pin
numbers refer to DIL packages only.

1 8

27

36

45

M & Y PACKAGE

(Top View)

M PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

θθ

θθ

θ

JA

95°C/W

DM PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

θθ

θθ

θ

JA

165°C/W

D PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

θθ

θθ

θ

JA

120°C/W

Y PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

θθ

θθ

θ

JA

130°C/W

Junction Temperature Calculation: T

J

= TA + (P

D

x θ

JA

).

The θ

JA

numbers are guidelines for the thermal performance of the device/pc-board system.

All of the above assume no ambient airflow

THERMAL DATA

DM PACKAGE

(Top View)

V

REF

V

CC

OUTPUT
GND

COMP

V

FB

I

SENSE

RT/C

T

1 8

27

36

45

V

REF

N.C.
V

CC

V

C

OUTPUT
GND
PWR GND

COMP

N.C.

V

FB

N.C.
I

SENSE

N.C.

RT/C

T

1 14

213

312

411

510

69

78

D PACKAGE

(Top View)

COMP

V

FB

I

SENSE

RT/C

T

V

REF

V

CC

OUTPUT
GND

C URRENT MODE PWM CONTROLLER

UC184xA/284xA/384xA

PRODUCT DATABOOK 1996/1997

3

Copyright © 1995
Rev. 1.2 12/95

P RODUCTION DATA SHEET

ELECTRICAL CHARACTERISTICS

(Unless otherwise specified, these specifications apply over the operating ambient temperatures for UC384xA with 0°C ≤ TA ≤ 70°C, UC284xA with -40°C ≤ TA ≤ 85°C,
UC184xA with -55°C ≤ T

A

≤ 125°C; V

CC

=15V; RT=10K; CT=3.3nF. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal

to the ambient temperature.)

Reference Section

Parameter

Symbol

Test Conditions

Output Voltage V

REFTJ

= 25°C, IL = 1mA

Line Regulation 12 ≤ VIN ≤ 25V
Load Regulation 1 ≤ I

O

≤ 20mA

Temperature Stability (Note 2 & 7)
Total Output Variation Over Line, Load, and Temperature
Output Noise Voltage (Note 2) V

N

10Hz ≤ f ≤ 10kHz, TJ = 25°C

Long Term Stability (Note 2) TA = 125°C, t = 1000hrs
Output Short Circuit Current I

SC

UC384xA

Units

Min. Typ. Max. Min. Typ. Max.

UC184xA/284xA

4.95 5.00 5.05 4.90 5.00 5.10 V
620 620 mV
625 625 mV

0.2 0.4 0.2 0.4 mV/°C

4.9 5.1 4.82 5.18 V
50 50 µV

525 525 mV

-30 -100 -180 -30 -100 -180 mA

Oscillator Section

Initial Accuracy (Note 6) TJ = 25°C
Voltage Stability 12 ≤ VCC ≤ 25V
Temperature Stability (Note 2) T

MIN

≤ TA ≤ T

MAX

Amplitude (Note 2)
Discharge Current TJ = 25°C, V

PIN 4

= 2V

V

PIN 4

= 2V, T

MIN

≤ TA ≤ T

MAX

47 52 57 47 52 57 kHz

0.2 1 0.2 1 %
55%

1.7 1.7 V

7.8 8.3 8.8 7.8 8.3 8.8 mA

7.5 8.8 7.6 8.8 mA

Output Low Level

V

OL

I

SINK

= 20mA

I

SINK

= 200mA

Output High Level

V

OH

I

SOURCE

= 20mA

I

SOURCE

= 200mA

Rise Time (Note 2) T

R

TJ = 25°C, CL = 1nF

Fall Time (Note 2) T

F

TJ = 25°C, CL = 1nF

UVLO Saturation V

SATVCC

= 5V, I

SINK

= 10mA

Current Sense Section

Gain (Note 3 & 4) A

VOL

Maximum Input Signal (Note 3) V

PIN 1

= 5V

Power Supply Rejection Ratio (Note 3) PSRR 12 ≤ V

CC

≤ 25V

Input Bias Current I

B

Delay to Output (Note 2) T

pdVPIN 3

= 0 to 2V

Output Section

2.85 3 3.15 2.85 3 3.15 V/V

0.9 1 1.1 0.9 1 1.1 V
70 70 dB

-2 -10 -2 -10 µA

150 300 150 300 ns

0.1 0.4 0.1 0.4 V

1.5 2.2 1.5 2.2 V
13 13.5 13 13.5 V
12 13.5 12 13.5 V

50 150 50 150 ns
50 150 50 150 ns

0.7 1.2 0.7 1.2 V

(Electrical Characteristics continue next page.)

Error Amp Section

Input Voltage V

PIN 1

= 2.5V

Input Bias Current I

B

Open Loop Gain A

VOL

2 ≤ VO ≤ 4V

Unity Gain Bandwidth (Note 2) UGBW T

j

= 25°C

Power Supply Rejection Ratio (Note 3) PSRR 12 ≤ VCC ≤ 25V
Output Sink Current I

OLVPIN 2

= 2.7V, V

PIN 1

= 1.1V

Output Source Current I

OHVPIN 2

= 2.3V, V

PIN 1

= 5V

Output Voltage High Level V

OHVPIN 2

= 2.3V, RL = 15K to ground

Output Voltage Low Level V

OLVPIN 2

= 2.7V, RL = 15K to V

REF

2.45 2.50 2.55 2.42 2.50 2.58 V

-0.3 -1 -0.3 -2 µA

65 90 65 90 dB

0.7 1 0.7 1 MHz
60 70 60 70 dB

26 26 mA

-0.5 -0.8 -0.5 -0.8 mA
56 56 V

0.7 1.1 0.7 1.1 V

C URRENT MODE PWM CONTROLLER

UC184xA/284xA/384xA

PRODUCT DATABOOK 1996/1997

Copyright © 1995

Rev. 1.2 12/95

4

P

RODUCTION DATA SHEET

ELECTRICAL CHARACTERISTICS (Con't.)

Under-Voltage Lockout Section

Parameter

Symbol

Test Conditions

Start Threshold x842A/4A

x843A/5A

Min. Operation Voltage After Turn-On x842A/4A

x843A/5A

UC384xA

Units

Min. Typ. Max. Min. Typ. Max.

UC184xA/284xA

15 16 17 14.5 16 17.5 V

7.8 8.4 9.0 7.8 8.4 9.0 V
9 10 11 8.5 10 11.5 V

7.0 7.6 8.2 7.0 7.6 8.2 V

PWM Section

Maximum Duty Cycle x842A/3A

x844A/5A

Minimum Duty Cycle

94 96 100 94 96 100 %
47 48 50 47 48 50 %

00%

Total Standby Section

Start-Up Current
Operating Supply Current I

CC

Zener Voltage VZICC = 25mA

0.3 0.5 0.3 0.5 mA
11 17 11 17 mA

30 35 30 35 V

BLOCK DIAGRAM

*

- V

CC

and VC are internally connected for 8 pin packages.

**

- POWER GROUND and GROUND are internally connected for 8 pin packages.

***

- Toggle flip flop used only in x844A and x845A series.

Notes: 2. These parameters, although guaranteed, are not 100% tested in

production.

3. Parameter measured at trip point of latch with V

VFB

= 0.

4. Gain defined as: A

VOL

= ; 0 ≤ V

ISENSE

≤ 0.8V.

5. Adjust VCC above the start threshold before setting at 15V.

6. Output frequency equals oscillator frequency for the UC1842A
and UC1843A. Output frequency is one half oscillator frequency
for the UC1844A and UC1845A.

7. "Temperature stability, sometimes referred to as average temperature
coefficient, is described by the equation:

Temp Stability =

V

REF

(max.) & V

REF

(min.) are the maximum & minimum reference
voltage measured over the appropriate temperature range. Note that
the extremes in voltage do not necessarily occur at the extremes in
temperature."

V

REF

(max.) - V

REF

(min.)

TJ (max.) - TJ (min.)

∆ V

COMP

∆ V

ISENSE

UVLO

S / R

5V

Ref

Internal

Bias

34V

Error Amp

1V

Current Sense
Comparator

PWM
Latch

S

R

R

Oscillator

2R

**

T***

V

REF

Good Logic

2.5V

UVLO

16V (1842A/4A)

8.4V (1843A/5A)

Hysteresis

6V (1842A/4A)

0.8V (1843A/5A)

COMP

CURRENT SENSE

V

FB

RT/C

T

GROUND

*

V

CC

V

REF

5.0V
50mA

V

C

*

OUTPUT

POWER GROUND

**

C URRENT MODE PWM CONTROLLER

UC184xA/284xA/384xA

PRODUCT DATABOOK 1996/1997

5

Copyright © 1995
Rev. 1.2 12/95

P RODUCTION DATA SHEET

CHARACTERISTIC CURVES

FIGURE 1. — OSCILLATOR FREQUENCY vs. TIMING

RESISTOR

300 3.0k 100

k

0

100k

RT - (ohms)

Oscillator Frequency - (Hz)

10k

1M

1.0k 10.0k 30.0k

CT = 1nF

CT = 2.2nF

CT = 4.7nF

FIGURE 2. — MAXIMUM DUTY CYCLE vs. TIMING RESISTOR

300 3.0k 100

k

0

40.0

RT - (ohms)

Maximum Duty Cycle - (%)

20.0

60.0

1.0k 10.0k 30.0k

80.0

100.0

Note: Output drive frequency is half the oscillator frequency for

the UCx844A/5A devices.

8

4

5

V

REF

RT/C

T

GROUND

R

T

C

T

For R

T

> 5k, f »

1.72
R

T CT

C URRENT MODE PWM CONTROLLER

UC184xA/284xA/384xA

PRODUCT DATABOOK 1996/1997

Copyright © 1995

Rev. 1.2 12/95

6

P

RODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS

FIGURE 3. — CURRENT SENSE SPIKE SUPPRESSION

FIGURE 4. — MOSFET PARASITIC OSCILLATIONS

6

Q1

V

CC

DC BUS

5

R

S

R

1

UCx84xA

7

UCx84xA

3

5

6

7

R

S

C

Q1

V

CC

DC BUS

I

PK

I

PK(MAX)

=

1.0V
R

S

CHANGE

FIGURE 5. — EXTERNAL DUTY CYCLE CLAMP AND MULTI-UNIT SYNCHRONIZATION

A resistor (R1) in series with the MOSFET gate will reduce overshoot
& ringing caused by the MOSFET input capacitance and any
inductance in series with the gate drive. (Note: It is very important to
have a low inductance ground path to insure correct operation of the
I.C. This can be done by making the ground paths as short and as
wide as possible.)

The RC low pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.

f =

(RA + 2RB)C

1.44

f =

RA + 2R

B

R

B Precision duty cycle limiting as well as synchronizing several parts is

possible with the above circuitry.

2

6

7

R

B

R

A

5 1

84

3

555

TIMER

4

5

8

To other

UCx84xA devices

0.01

UCx84xA

C URRENT MODE PWM CONTROLLER

UC184xA/284xA/384xA

PRODUCT DATABOOK 1996/1997

7

Copyright © 1995
Rev. 1.2 12/95

P RODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS (continued)

FIGURE 6. — SLOPE COMPENSATION

FIGURE 7. — OPEN LOOP LABORATORY FIXTURE

2

3

4

8

7

6

5

COMP

V

FB

I

SENSE

RTC

T

V

REF

V

CC

OUTPUT

GROUND

0.1µF 0.1µF

A

UCx84xA

R

T

2N2222

100K

4.7K

1K

4.7K

5K

I

SENSE

ADJUST

ERROR AMP

A

DJUST

C

T

1K

GROUND

OUTPUT

V

CC

V

REF

1

OSCILLATOR

V

REF

GOOD LOGIC

S

R5VREF

INTERNAL

BIAS

8(14)

4(7)

2(3)

1(1)

R

F

C

F

R

d

R

i

From V

O

R

SLOPE

2N222A

R

T

5V

UVLO

2.5V

ERROR

AMP

C

T

1V

2R

R

C.S.

COMP

PWM

LATCH

5(9)

3(5)

5(8)

CR

S

R

6(10)

7(11)

7(12)

V

CC

DC BUS

V

O

Q1

UCx84xA

Due to inherent instability of current mode converters running above 50% duty cycle, slope compensation should be added to either
the current sense pin or the error amplifier. Figure 6 shows a typical slope compensation technique.

High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be
connected to pin 5 in a single point ground. The transistor and 5k potentiometer are used to sample the oscillator waveform and apply an
adjustable ramp to pin 3.

C URRENT MODE PWM CONTROLLER

UC184xA/284xA/384xA

PRODUCT DATABOOK 1996/1997

Copyright © 1995

Rev. 1.2 12/95

8

P

RODUCTION DATA SHEET

TYPICAL APPLICATION CIRCUITS (continued)

FIGURE 8. — OFF-LINE FLYBACK REGULATOR

SPECIFICATIONS

Input line voltage: 90VAC to 130VAC
Input frequency: 50 or 60Hz
Switching frequency: 40KHz ±10%
Output power: 25W maximum
Output voltage: 5V +5%
Output current: 2 to 5A
Line regulation: 0.01%/V
Load regulation: 8%/A*
Efficiency @ 25 Watts,

V

IN

= 90VAC: 70%

V

IN

= 130VAC: 65%

Output short-circuit current: 2.5Amp average

* This circuit uses a low-cost feedback scheme in which the DC

voltage developed from the primary-side control winding is
sensed by the UC3844A error amplifier. Load regulation is
therefore dependent on the coupling between secondary and
control windings, and on transformer leakage inductance.

7

150kW

100pF

V

FB

COMP

V

REF

RT/C

T

4700µF

10V

5V

2-5A

ISOLATION

BOUNDARY

3600pF
400V

1N4935

820pF

2.5k

W

1N4935

IRF830

27k

W

0.01µF

10µF
20V

1N4935

1k

W

470pF

0.85k

W

MBR735TI

4.7k

W

2W

140kW
1/2W

220µF
250V

4.7kW 1W

1N4004

1N40041N4004

1N4004

AC

INPUT

V

CC

OUT

CUR
SEN

GND

UC3844A

20kW

3.6k

W

10kW

.0022µF0.01µF

16V

3

6

2

1

8

4

5