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

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