Datasheet UC3845AN, UC3844AN, UC3843AN, UC3845AD, UC3844AD Datasheet (SGS Thomson Microelectronics)

UC2842A/3A/4A/5A



UC3842A/3A/4A/5A

HIGH PERFORMANCE CURRENTMODE PWM CONTROLLER

TRIMMED OSCILLATOR DISCHARGE CUR-

.

RENT
CURRENT MODEOPERATIONTO500kHz

.

AUTOMATIC FEED FORWARD COMPENSA-

.

TION
LATCHING PWM FOR CYCLE-BY-CYCLE

.

CURRENT LIMITING
INTERNALLY TRIMMED REFERENCE WITH

.

UNDERVOLTAGELOCKOUT
HIGHCURRENTTOTEMPOLEOUTPUT

.

UNDERVOLTAGE LOCKOUT WITH HYSTER-

.

ESIS
LOWSTART-UPCURRENT (< 0.5mA)

.

DOUBLEPULSESUPPRESSION

.

DESCRIPTION

TheUC384xAfamilyofcontrolICsprovidesthenec­essaryfeaturesto implement off-lineor DC to DC
fixedfrequencycurrent modecontrolschemeswith
a minimal external parts count. Internally imple­mentedcircuitsincludea trimmedoscillatorfor pre­cise DUTY CYCLECONTROL under voltagelock­outfeaturingstart-upcurrentlessthan0.5mA,a pre­cision reference trimmed for accuracyat the error
ampinput,logictoinsurelatchedoperation,a PWM

comparatorwhichalsoprovidescurrentlimit control,
and a totempole output stage designed to source
orsinkhighpeakcurrent.Theoutputstage,suitable
for driving N-Channel MOSFETs, is low in the off­state.

Differencesbetweenmembersof thisfamily arethe
under-voltagelockoutthresholdsandmaximumduty
cycle ranges. The UC3842A and UC3844A have
UVLOthresholds of 16V (on) and 10V (off), ideally
suitedoff-lineapplicationsThecorrespondingthresh­olds for the UC3843A and UC3845A are 8.5 V and

7.9V.The UC3842A and UC3843A can oper ateto
dutycyclesapproaching100%.Arangeofthezeroto
<50%is obtainedbytheUC3844AandUC3845Aby
theadditionofaninternaltoggleflipflopwhichblanks
theoutputoffeveryotherclockcycle.

Minidip

SO8

BLOCK DIAGRAM (toggle flip flop used only in UC3844A and UC3845A)

7

Vi

2.50V

UVLO

S/R

2R

R1V

5V

REF

VREF GOOD

LOGIC

S
R

CURRENT

SENSE

COMPARATOR

INTERNAL

BIAS

T

LATCH

UC3842A

March 1999

GROUND

RT/CT

VFB

COMP

CURRENT

SENSE

34V

5

4

2

1

3

OSC

ERROR AMP.

+

- PWM

D95IN331

8

6

VREF

5V 50mA

OUTPUT

1/15

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

ABSOLUTEMAXIMUMRATINGS

Symbol Parameter Value Unit

V
V
I

O

E

O

P

tot

P

tot

T

stg

T

J

T

L

*

Allvoltagesare with respect to pin 5, all currents arepositiveinto the specifiedterminal.

PIN CONNE C TI ON

SupplyVoltage (low impedance source) 30 V

i

SupplyVoltage (Ii < 30mA) Self Limiting

i

Output Current

1

±

Output Energy (capacitive load) 5
Analog Inputs(pins 2, 3) – 0.3to 5.5 V
ErrorAmplifier Output SinkCurrent 10 mA
Power Dissipation at T

amb

≤25°

C (Minidip)

Power Dissipation at Tamb≤25°C (SO8)

1.25 W
800 mW

Storage Temperature Range – 65 to 150
JunctionOperating Temperature – 40 to 150 °C
Lead Temperature (soldering 10s) 300

(top view)

Minid i p/ SO8

A

J

µ

C

°

C

°

COMP

V

FB

I

SENSE

RT/C

T

1
2
3
4

D95IN332

8
7
6
5

V

REF

Vi
OUTPUT
GROUND

PIN FUNCTIONS

No Function Description

1 COMP This pin is the Error Amplifier output and is made available for loop compensation.
2V

3I

4R

SENSE

T/CT

5 GROUND This pin is the combined control circuitry and power ground.
6 OUTPUT This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced

7V

CC

8V

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

FB

power supply output through a resistor divider.
A voltage proportional to inductor current is connected to this input. The PWM uses this

information to terminate the output switch conduction.
The oscillator frequency and maximum Output duty cycle are programmed by connecting

resistor R

to Vref and cpacitor CTto ground. Operation to 500kHz is possible.

T

and sunk by this pin.
This pin is the positive supply of the control IC.

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

ref

ORDERINGNUMBERS

UC2842AD1; UC3842AD1
UC2843AD1; UC3843AD1
UC2844AD1; UC3844AD1
UC2845AD1; UC3845AD1

2/15

SO8 Minidip

UC2842AN; UC3842AN
UC2843AN; UC3843AN
UC2844AN; UC3844AN
UC2845AN; UC3845AN

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

THERMAL DATA

Symbol Description Mi n i dip SO 8 U n it

R

th j-amb

Thermal ResistanceJunction-ambient. max. 100 150

°

C/W

ELECTRICALCHARACTERISTICS

-25 < T

<85°C forUC284XA;0 < T

amb

( [note 1] Unless otherwise stated, these specificationsapply for

<70°CforUC384XA;Vi=15V(note 5); RT= 10K; CT= 3.3nF)

amb

Symbol Parameter Test Conditions

REFERENCE SECTION

V

∆V
∆V

V

∆

REF

Output Voltage

REF

Line Regulation

REF

Load Regulation

REF

Temperature Stability (Note 2) 0.2 0.2

/∆T

=25°CIo= 1mA

T

j

12V ≤ V
1 ≤ I

i

≤ 20mA

o

≤ 25V

Total Output Variation Line, Load, Temperature 4.9 5.1 4.82 5.18 V

e

Output Noise Voltage

N

10Hz≤f≤10KHz T
(note 2)

Long Term Stability

= 125°C, 1000Hrs

T

amb

(note 2)

I

Output Short Circuit -30 -100 -180 -30 -100 -180 mA

SC

OSCILLATOR SECTION

f

f

∆

OSC

f

∆

OSC

V

I

dischg

OSC

Frequency
Frequency Change with Volt. V

/∆V

Frequency Change with Temp. T

/∆T

Oscillator Voltage Swing (peak to peak) – 1.6 – – 1.6 – V

OSC

Discharge Current (V

=2V) TJ=25°C 7.8 8.3 8.8 7.8 8.3 8.8 mA

OSC

=25°C

T

j

= 12V to 25V – 0.2 1 – 0.2 1 %

CC

A=Tlow

to T

high

ERROR AMP SECTION

V

BW Unity Gain Bandwidth T

PSRR Power Supply Rejec. Ratio

Input Voltage V

2

I

Input Bias Current VFB= 5V -0.1 -1 -0.1 -2

b

A

VOL

I

Output Sink Current VPIN2 = 2.7V V

o

I

Output Source Current VPIN2 = 2.3V V

o

V

High V

OUT

Low V

V

OUT

= 2.5V 2.45 2.50 2.55 2.42 2.50 2.58 V

PIN1

2V ≤ Vo≤ 4V

=25°C 0.7 1 0.7 1 MHz

J

12V≤V

PIN2

= 15KΩto Ground

R

L

PIN2

= 15KΩto Pin 8

R

L

≤

i

= 2.3V;

= 2.7V;

25V

PIN1

PIN1

CURRENT SENSE SECTION

G

V

SVR Supply Voltage Rejection

Gain (note 3 & 4) 2.85 3 3.15 2.85 3 3.15 V/V

V

Maximum Input Signal V

3

I

Input Bias Current -2 -10 -2 -10

b

= 5V (note 3) 0.9 1 1.1 0.9 1 1.1 V

PIN1

12≤V

25V (note 3)

≤

i

Delay to Output 150 300 150 300 ns

UC284XA UC38 4XA

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

Unit

4.95 5.00 5.05 4.90 5.00 5.10 V
220 220mV
325 325mV

mV/°C

=25°C

j

50 50 µ

525 525mV

47 52 57 47 52 57 KHz

–5––5–%

µA

65 90 65 90 dB

60 70 60 70 dB

= 1.1V 2 12 2 12 mA

= 5V -0.5 -1 -0.5 -1 mA

5 6.2 5 6.2 V

0.8 1.1 0.8 1.1 V

70 70 dB

µ

V

A

3/15

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

ELECTRICAL CHARACTERISTICS

(continued)

Symbol Pa ram et er Test C o n diti o n s

OUTPUT SECTION

V

V

V

Output Low Level I

OL

Output High Level I

OH

UVLO Saturation VCC= 6V; I

OLS

t

Rise Time

r

t

Fall Time

f

= 20mA 0.1 0.4 0.1 0.4 V

SINK

I

= 200mA 1.6 2.2 1.6 2.2 V

SINK

= 20mA 13 13.5 13 13.5 V

SOURCE

I

T
T

= 200mA 12 13.5 12 13.5 V

SOURCE

= 1mA 0.7 1.2 0.7 1.2 V

SINK

=25°CCL= 1nF (2)

j

=25°CCL= 1nF (2)

j

UNDER-VOLTAGE LOCKOUT SECTION

Start Threshold X842A/4A 15 16 17 14.5 16 17.5 V

X843A/5A 7.8 8.4 9.0 7.8 8.4 9.0 V

Min Operating Voltage
After Turn-on

X842A/4A 9 10 11 8.5 10 11.5 V
X843A/5A 7.0 7.6 8.2 7.0 7.6 8.2 V

PWM SECTION

Maximum Duty Cycle X842A/3A 94 96 100 94 96 100 %

X844A/5A 47 48 50 47 48 50 %

Minimum Duty Cycle 0 0 %

TOTAL STANDBY CURRENT

I

Start-up Current Vi= 6.5V for UCX843A/45A 0.3 0.5 0.3 0.5 mA

st

V

= 14V for UCX842A/44A 0.3 0.5 0.3 0.5 mA

i

I

V

Operating Supply Current V

i

Zener Voltage Ii= 25mA 30 36 30 36 V

iz

PIN2=VPIN3

=0V 12 17 12 17 mA

UC284X A UC384 X A

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

50 150 50 150 ns
50 150 50 150 ns

Unit

Notes : 1. Max package power dissipation limitsmust be respected; low duty cycle pulse techniquesare used duringtestmaintainTjas

close to T

2. Theseparameters, although guaranteed, are not100%testedin production.

3. Parametermeasured at trippointof latchwithV

4. Gain definedas :
A= ;0≤V

5. AdjustViabovethestart threshold before setting at 15 V.

∆ V
∆ V

aspossible.

amb

PIN1
PIN3

PIN3

≤

0.8V

PIN2

=0.

4/15

Figure1: OpenLoop Test Circuit.

4.7KΩ

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

V

REF

R

T

V

REF

ERROR AMP.

ADJUST

4.7KΩ

1KΩ

100KΩ

I

SENSE

ADJUST

D95IN343

5KΩ

COMP

V

I

SENSE

RT/C

FB

T

1
2

UC3842A

3

4

Highpeakcurrentsassociatedwithcapacitiveloads
necessitate careful grounding techniques. Timing
and bypass capacitorsshould be connectedclose

Figure 2:

Oscillator Frequency vs Timing Resis­tance

f

(Hz)

o

D96IN362

A2N2222

7

6

5

0.1µF

V

i

OUTPUT

GROUND

0.1µF

1W

1KΩ

8

C

T

V

i

OUTPUT

GROUND

to pin 5 ina singlepointground.The transistorand
5KΩpotentiometerareusedtosampletheoscillator

waveformand applyan adjustablerampto pin 3.

Figure 3:

Maximum Duty Cycle vs Timing Resis­tor

f

o

(Hz)

D96IN363

1M

CT=470pF

1nF

100K

10K

1K

300 1K 3K 10K 30K RT(Ω)

2.2nF

4.7nF

80

60

40

20

0

300 1K 3K 10K 30K RT(Ω)

5/15

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

Figure 4: Oscillator Discharge Current vs. Tem-

perature.

I

dischg

(mA)

D95IN335

Vi=15V
V

=2V

8.5

8.0

7.5

7.0

-55 -25 0 25 50 75 100 TA(°C)

OSC

Figure 6: Current Sense Input Threshold vs. Er-

ror Amp Output Voltage.

Vth
(V)

1.0

0.8

0.6

Vi=15V

T

=125°C

T

A

=25°C

A

D95IN338

Figure 5: Error Amp Open-Loop Gain and

Phase vs. Frequency.

(dB)

Vi=15V

80

Gain

60

40

20

0

-20
10 100 1K 10K 100K 1M f(Hz)

VO=2V to
RL=100K
TA=25°C

D95IN337

4V

Phase

Figure 7: Reference Voltage Change vs.

Source Current.

60

50

40

30

T

=125°C

A

T

A

Vi=15V

=-40°C

D95IN339

φ

30

60

90

120

150

180

0.4

T

=-40°C

0.2

0.0
0246V

A

(V)

O

Figure 8: ReferenceShort Circuit Current vs.

Temperature.

I

SC

(mA)

100

90

80

70

60

50

-55 -25 0 25 50 75 100 TA(°C)

Vi=15V
RL≤0.1Ω

D95IN340

20

10

0

0 20406080100I

=25°C

A

T

ref

(mA)

6/15

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

Figure 9: Output Saturation Voltage vs. Load

Figure 10: Supply Current vs. Supply Voltage.

Current.

V

sat

(V)

V

-1

-2
Vi=15V

80µs Pulsed Load 120Hz Rate

3

2

1

0

0 200 400 600 IO(mA)

i

T

=25°C

A

TA=-40°C

Source

Saturation

(Load to Ground)

TA=-40°C

T

Saturation

Sink
(Load to Vi)

=25°C

A

D95IN341

GND

I

i

(mA)

20

15

10

5

0

UCX843/45

0 102030V

UCX842/44

RT=10K
CT=3.3nF
VFB=0V
I

Sense

TA=25°C

Figure 11: Output Waveform. Figure 12: Output Cross Conduction

Vi=15V
C

= 1.0nF

90%

L

T

A

=25°C

V

O

D95IN342

=0V

V

=30V

i

C

L

T

A

(V)

i

= 15pF
=25°C

20V/DIV

10%

Figure 13:

50ns/DIV

Oscillator and Output Waveforms.

V

i

7

8

PWM

R

T

4

I

C

T

5V REG

CLOCK

OSCILLATOR

D

5

GND

6

I

CC

OUTPUT

OUTPUT

OUTPUT

CT

CT

100ns/DIV

LARGE R

SMALL R

/SMALL C

T

/LARGE C

T

D95IN344

100mA/DIV

T

T

7/15

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

Figure14 : ErrorAmp Configuration.

V

Z

i

Z

f

FB

COMP

2.5V

1mA

+

2

-

1

D95IN345

Figure15 :

UnderVoltageLockout.

V

i

7

ON/OFF

TO REST OF IC

UC3842A
UC3844A

V

ON

V

OFF

Figure16 : Current SenseCircuit.

I

S

COMP

R

CURRENT

CR

S

D95IN347

SENSE

COMMAND

UC3843A
UC3845A

16V 8.4V

10V 7.6V

1

3

5

GND

ERROR

AMPL.

I

<17mA

<0.5mA

Fig.15-UC3842A

2R

CC

V

OFFVON

R1V

COMPARATOR

CURRENT

SENSE

V

CC

Peakcurrent (is) isdeterminedby theformula

S max

R

S

1.0 V

≈

I

A small RC filter may be required to suppressswitchtransients.

8/15

Figure17 : Slope CompensationTechniques.

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

I

S

R

R

R

S

Figure18 :

V

REG

8

R

T

RT/C

T

SLOPE

1

C

T

I

SENSE

UC3842A

4

3

5

I

S

R

SLOPE

R

1

R

S

GND

IsolatedMOSFETDrive and CurrentTransformerSensing.

V

CC

7

V

REG

8

R

T

RT/C

T

4

UC3842A

C

T

I

SENSE

3

5

GND

D95IN348

V

in

5.0V

+

-

-

+

ref

S

Q

R

COMP/LATCH

C

ISOLATION

BOUNDARY

R

R

S

VGSWaveforms

Q1

N

S

+
0

50% DC 25% DC

V

(pin 1)

I

=

pk

N

P

3R

-1.4

S

+
0

--

N

S

()

N

P

+

-

6

3

D95IN349

9/15

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

Figure19 :

LatchedShutdown.

4

2N

3905

8

2

1

2N

3903

R

R

+

­EA

SCR must be selected for a holding current of less than 0.5mA at T
The simple two transistor circuit can be used in place of the SCR as shown. All resistors are 10K.

OSC

BIAS

+

1mA

2R

R

5

D95IN350

.

A(min)

Figure 20:

Error Amplifier Compensation

EA

EA

+

1mA

2R

R

+

1mA

2R

R

From V

O

R

i

R

C

d

f

2.5V

+

-

2

R

f

1

Error Amp compensation circuit for stabilizing any current-mode topology except
for boost and flyback converters operating with continuous inductor current.

From V

R

P

C

P

O

R

i

R

C

d

f

2.5V

+

-

2

R

f

1

Error Amp compensation circuit for stabilizing current-mode boost and flyback
topologies operating with continuous inductor current.

5

D95IN351

5

10/15

Figure 21: External Clock Synchronization.

V

REF

R

T

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

8

R

BIAS

R

EXTERNAL

SYNC INPUT

The diode clamp is required if the Sync amplitude is large enough to
the bottom side of CTto go more than 300mV below ground

Figure 22:

V

R

A

B

4

+

EA

0.01µF

C

47Ω

T

+

2

-

1

External Duty Cycle Clamp and Multi Unit Synchronization.

REF

5K
6
5

5K

84

+

-

R

Q

3

7

8

4

OSC

2R

cause

+

R

5

D95IN352

R

BIAS

RR

OSC

f=

C

(R

1.44
+2RB)C

A

2

5K

+

-

1

D

=

max

RA+2R

R

B

S

NE555

B

+

2

­EA

1

TO ADDITIONAL

UCX84XAs

UCX84XAs

2R

R

5

D95IN353

11/15

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

Figure 23: Soft-StartCircuit

8

R

BIAS

R

4

+

OSC

1mA

2R

R

1MΩ

+

2

­EA

1

C

5

Figure 24: Soft-Startand Error Amplifier Output Duty Cycle Clamp.

5V

1V

ref

+

-

S

+

-

D95IN354

Q

R

V

V

CC

in

C

12/15

R2

R1

8

4

2

1

BC109

7

Q

V

CLAMP

+

-

7

6

5

R

S

D95IN355

Q1

R

S

5V

ref

R

BIAS

R

R

1

R1+R

OSC

2R

R

where 0 <V

2

V

Clamp

5

CLAMP

+

1mA

+

­EA

V

= ·

CLAMP

1V

<1V I

+

-

­+

Comp/Latch

=

pk(max)

S

R

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

DIM.

MIN. TYP. MAX. MIN. TYP. MAX.

A 1.75 0.069
a1 0.1 0.25 0.004 0.010
a2 1.65 0.065
a3 0.65 0.85 0.026 0.033

b 0.35 0.48 0.014 0.019

b1 0.19 0.25 0.007 0.010

C 0.25 0.5 0.010 0.020
c1 45°(typ.)

D (1) 4.8 5.0 0.189 0.197

E 5.8 6.2 0.228 0.244

e 1.27 0.050

e3 3.81 0.150

F (1) 3.8 4.0 0.15 0.157

L 0.4 1.27 0.016 0.050

M 0.6 0.024

S8°(max.)

(1) D and F do not include mold flash or protrusions. Mold flash or

potrusionsshall not exceed 0.15mm (.006inch).

mm inch

OUTLINE AND

MECHANICAL DATA

SO8

13/15

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

DIM.

MIN. TYP. MAX. MIN. TYP. MAX.

A 3.32 0.131

a1 0.51 0.020

B 1.15 1.65 0.045 0.065
b 0.356 0.55 0.014 0.022

b1 0.204 0.304 0.008 0.012

D 10.92 0.430

E 7.95 9.75 0.313 0.384

e 2.54 0.100
e3 7.62 0.300
e4 7.62 0.300

F 6.6 0.260

I 5.08 0.200
L 3.18 3.81 0.125 0.150
Z 1.52 0.060

mm inch

OUTLINE AND

MECHANICAL DATA

Minidip

14/15

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

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15/15