SGS Thomson Microelectronics UC3845BN, UC3843BN, UC3843BD, UC3845BD, UC3844BN Datasheet
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UC2842B/3B/4B/5B
UC3842B/3B/4B/5B
HIGH PERFORMANCE CURRENTMODE PWM CONTROLLER
TRIMMED OSCILLATORFOR PRECISE FRE-
.
QUENCY CONTROL
OSCILLATOR FREQUENCY GUARANTEED
.
AT 250kHz
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-UPANDOPERATINGCURRENT
.
DESCRIPTION
TheUC384xBfamilyofcontrolICsprovidesthenecessaryfeatures to implement off-line or 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 accuracy at the error
ampinput,logicto insurelatchedoperation,aPWM
comparatorwhichalsoprovidescurrentlimitcontrol,
and a totempole output stage designedto source
orsinkhighpeakcurrent.Theoutputstage,suitable
for driving N-Channel MOSFETs, is low in the offstate.
Differencesbetweenmembersofthisfamilyarethe
under-voltagelockoutthresholdsandmaximumduty
cycle ranges. The UC3842B and UC3844B have
UVLOthresholds of 16V (on) and 10V (off), ideally
suitedoff-lineapplicationsThecorrespondingthresholdsfortheUC3843BandUC3845Bare8.5Vand7.9
V. TheUC3842BandUC3843B can operateto duty
cyclesapproaching100%.Arangeof the zeroto <
50 % is obtainedby the UC3844Band UC3845Bby
theadditionofan internaltoggleflipflopwhichblanks
theoutputoffeveryotherclockcycle.
Minidip
SO8
BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B)
7
Vi
2.50V
UVLO
S/R
2R
R1V
5V
REF
VREF GOOD
LOGIC
S
R
CURRENT
SENSE
COMPARATOR
INTERNAL
BIAS
T
LATCH
UC3842B
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
UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
ABSOLUTEMAXIMUMRATINGS
Symbol Parameter Value Unit
V
V
I
O
E
O
P
tot
P
tot
T
stg
T
J
T
L
*
Allvoltages arewith respect topin 5, allcurrents are positiveinto the specifiedterminal.
PI N CONNE CTIO N (top view)
SupplyVoltage(low impedance source) 30 V
i
SupplyVoltage(Ii < 30mA) Self Limiting
i
Output Current
1
±
Output Energy (capacitive load) 5
Analog Inputs(pins2,3) – 0.3to 5.5 V
ErrorAmplifier Output Sink Current 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
Mini di p/ SO 8
A
J
µ
C
°
C
°
COMP
V
I
SENSE
RT/C
1
FB
T
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
UC2842BD1; UC3842BD1
UC2843BD1; UC3843BD1
UC2844BD1; UC3844BD1
UC2845BD1; UC3845BD1
2/15
SO8 Minidip
UC2842BN; UC3842BN
UC2843BN; UC3843BN
UC2844BN; UC3844BN
UC2845BN; UC3845BN
UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
THERMAL DATA
Symbol Descriptio n M in i dip SO 8 U n it
R
th j-amb
Thermal ResistanceJunction-ambient. max. 100 150
°
C/W
ELECTRICALCHARACTERISTICS
-25 < T
<85°C forUC284XB;0 < T
amb
( [note 1] Unless otherwise stated, these specifications apply for
<70°CforUC384XB;Vi=15V(note5);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
OSC
Frequency
=25°C
T
j
T
A=Tlow
to T
high
TJ=25°C(RT=6.2k,CT=1nF)
f
∆
OSC
f
∆
OSC
V
I
dischg
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
OSC
= 12V to 25V – 0.2 1 – 0.2 1 %
CC
A=Tlow
T
A=Tlow
to T
to T
high
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 µ
b
A
VOL
I
Output Sink Current V
o
I
Output Source Current V
o
V
High V
OUT
V
Low V
OUT
= 2.5V 2.45 2.50 2.55 2.42 2.50 2.58 V
PIN1
2V≤V
J
12V≤V
PIN2
PIN2
PIN2
R
L
PIN2
R
L
4V
≤
o
=25°C 0.7 1 0.7 1 MHz
25V
≤
i
= 2.7V V
= 2.3V V
PIN1
PIN1
= 2.3V;
= 15KΩ to Ground
= 2.7V;
= 15KΩ to Pin 8
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
UC284XB UC38 4XB
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
49
52
55
49
52
55
KHz
48
–
56
48
–
56
KHz
225
250
275
225
250
275
KHz
–1––0.5–%
7.8
8.3–8.8
7.5
8.8
7.8
7.6
8.3–8.8
8.8mAmA
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
µA
V
A
3/15
UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
ELECTRICALCHARACTERISTICS
(continued)
Symbol Paramet er Test C o n dition 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 0.1 1.1 0.1 1.1 V
SINK
=25°CCL= 1nF (2)
j
=25°CCL= 1nF (2)
j
UNDER-VOLTAGE LOCKOUT SECTION
Start Threshold X842B/4B 15 16 17 14.5 16 17.5 V
X843B/5B 7.8 8.4 9.0 7.8 8.4 9.0 V
Min Operating Voltage
After Turn-on
X842B/4B 9 10 11 8.5 10 11.5 V
X843B/5B 7.0 7.6 8.2 7.0 7.6 8.2 V
PWM SECTION
Maximum Duty Cycle X842B/3B 94 96 100 94 96 100 %
X844B/5B 47 48 50 47 48 50 %
Minimum Duty Cycle 0 0 %
TOTAL STANDBY CURRENT
I
Start-up Current Vi= 6.5V for UCX843B/45B 0.3 0.5 0.3 0.5 mA
st
V
= 14V for UCX842B/44B 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 B UC384 X B
Min. Typ. Max. Min. Typ. Max.
50 150 50 150 ns
50 150 50 150 ns
Unit
Notes : 1. Max package power dissipation limitsmustbe respected; low duty cyclepulsetechniques are used during test maintainTjas
close toT
2. Theseparameters, althoughguaranteed, are not 100%testedin production.
3. Parametermeasured at trippointof latch withV
4. Gain definedas :
A= ;0≤V
5. AdjustViabovethe startthreshold beforesettingat 15 V.
∆ V
∆ V
aspossible.
amb
PIN1
PIN3
PIN3
≤
0.8V
PIN2
=0.
4/15
Figure1: OpenLoopTest Circuit.
4.7KΩ
UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
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
UC2842B
3
4
Highpeakcurrentsassociatedwithcapacitiveloads
necessitate careful grounding techniques. Timing
and bypass capacitorsshouldbe connectedclose
Figure 2:
Timing Resistor vs. Oscillator Frequency
T
=100pF
D95IN333
OSC
(KHz)
RT
(KΩ)
C
C
T
=1nF
T
=200pF
C
T
=500pF
CT=2nF
C
50
20
10
5
2
Vi=15V
TA=25°C
1
0.8
10K 20K 30K 50K 100K 200K 300K 500K f
CT=5nF
CT=10nF
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.Thetransistorand
5KΩpotentiometerareusedtosampletheoscillator
waveformand apply an adjustablerampto pin 3.
Figure 3:
Output Dead-Time vs. Oscillator Frequency
%
50
30
20
10
5
3
2
1
CT=200pF
10K 20K 30K 50K 100K 200K 300K 500K fOSC(KHz)
CT=500pF
CT=1nF
CT=10nF
CT=100pF
CT=5nF
CT=2nF
Vi=15V
TA=25°C
D95IN334
5/15
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