®
UC2842/3/4/5
UC3842/3/4/5
CURRENT MODE PWM CONTROLLER
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OPTIMIZED FOR OFF-LINE AND DC TO DC
CONVERTERS
LOW START-UP CURRENT (< 1 mA)
AUTOMATIC FEED FORWARD COMPENSA-
TION
PULSE-BY-PULSE CURRENT LIMITING
ENHANCED LOAD RESPONSE CHARAC-
TERISTICS
UNDER-VOLTAGE LOCKOUT WITH HYSTER-
ESIS
DOUBLE PULSE SUPPRESSION
HIGH CURRENT TOTEM POLE OUTPUT
INTERNALLY TRIMMED BANDGAP REFER-
ENCE
500 KHz OPERATION
LOW R
O
ERROR AMP
Minidip
SO14
DESCRIPTION
TheUC3842/3/4/5family of controlICs provides the
necessary features to implement off-line or DC to
DC fixed frequency current mode control schemes
with a minimal externalparts count.Internallyimple-
mentedcircuits include undervoltagelockout featur-
ing start-up current less than 1 mA, a precision ref-
erence trimmed for accuracy at the error amp input,
logic to insure latched operation, a PWM compara-
torwhich also providescurrentlimit control,and a to-
tem pole output stage designed to source or sink
high peak current. The output stage, suitable for
driving N-Channel MOSFETs, is low in theoff-state.
Differences between members of this family are the
under-voltage lockout thresholds and maximum
duty cycle ranges. The UC3842 and UC3844 have
UVLO thresholds of 16V (on) and 10V (off), ideally
suited off-line applications The corresponding
thresholds for the UC3843 and UC3845 are 8.5 V
and 7.9 V. The UC3842 and UC3843 can operate
to duty cycles approaching 100%. A range of the
zero to < 50 % is obtained by the UC3844 and
UC3845 by the additionof an internal toggle flip flop
which blanks the output off every other clock cycle.
BLOCK DIAGRAM
(toggle flip flop used only in U3844 and UC3845)
October 1998
1/11
UC2842/3/4/5-UC3842/3/4/5
ABSOLUTE MAXIMUM RATINGS
Symbol
V
i
V
i
I
O
E
O
Parameter
Supply Voltage (low impedance source)
Supply Voltage (Ii < 30mA)
Output Current
Output Energy (capacitive load)
Analog Inputs (pins 2, 3)
Error Amplifier Output Sink Current
P
tot
P
tot
T
stg
T
L
Power Dissipation at T
amb
≤
50
°C
(minidip, DIP-14)
Power Dissipation at Tamb
≤
25
°C
(SO14)
Storage Temperature Range
Lead Temperature (soldering 10s)
Value
30
Self Limiting
±
1
5
– 0.3 to 6.3
10
1
725
– 65 to 150
300
A
µ
J
V
mA
W
mW
°C
°C
Unit
V
* All voltages are with respect to pin 5, all currents are positive into the specified terminal.
PIN CONNECTIONS
(top views)
SO14
Minidip
ORDERING NUMBERS
T ype
UC2842
UC3843
UC2844
UC2845
UC3842
UC3843
UC3844
UC3845
Min idip
UC2842N
UC2843N
UC2844N
UC2845N
UC3842N
UC3843N
UC3844N
UC3845N
SO14
UC2842D
UC2843D
UC2844D
UC2845D
UC3842D
UC3843D
UC3844D
UC3845D
THERMAL DATA
Symbol
R
th j-amb
Description
Thermal Resistance Junction-ambient.
max.
Min id ip
100
SO14
165
Unit
°
C
2/11
UC2842/3/4/5-UC3842/3/4/5
ELECTRICAL CHARACTERISTICS
(Unless otherwise stated, these specifications apply for -25 < T
amb
<
85°C for UC2824X; 0 < T
amb
< 70°C for UC384X; V
i
= 15V (note 5); R
T
= 10K; C
T
= 3.3nF)
Symbo l
Parameter
T est Cond ition s
REFERENCE SECTION
V
REF
∆
V
REF
∆
V
REF
∆V
REF
/∆T
e
N
Output Voltage
Line Regulation
Load Regulation
Temperature Stability
Total Output Variant
Output Noise Voltage
Long Term Stability
I
SC
f
s
Output Short Circuit
OSCILLATOR SECTION
Initial Accuracy
Voltage Stability
Temperature Stability
V
4
V
2
I
b
B
SVR
I
o
I
o
Amplitude
Input Voltage
Input Bias Current
A
VOL
Unity Gain Bandwidth
Supply Voltage Rejection
Output Sink Current
Output Source Current
V
OUT
High
V
OUT
Low
2
≤
V
o
≤
4V
(2)
12V
≤
V
i
≤
25V
V
PIN2
= 2.7V V
PIN1
= 1.1V
V
PIN2
= 2.3V V
PIN1
= 5V
V
PIN2
= 2.3V;
R
L
= 15K
Ω
to Ground
V
PIN2
= 2.7V;
R
L
= 15K
Ω
to Pin 8
CURRENT SENSE SECTION
G
V
V
3
SVR
I
b
Gain
Maximum Input Signal
Supply Voltage Rejection
Input Bias Current
Delay to Output
OUTPUT SECTION
I
OL
I
OH
t
r
t
f
Output Low Level
Output High Level
Rise Time
Fall Time
I
SINK
= 20mA
I
SINK
= 200mA
ISOURCE = 20mA
I
SOURCE
= 200mA
T
j
= 25
°
C
T
j
= 25°C
C
L
= 1nF (2)
C
L
= 1nF (2)
13
12
0.1
1.5
13.5
13.5
50
50
150
150
0.4
2.2
13
12
0.1
1.5
13.5
13.5
50
50
150
150
0.4
2.2
V
V
V
V
ns
ns
(3 & 4)
V
PIN1
= 5V (3)
12
≤
V
i
≤
25V (3)
2.85
0.9
3
1
70
-2
150
-10
300
3.15
1.1
2.8
0.9
3
1
70
-2
150
-10
300
3.2
1.1
V/V
V
dB
µ
A
ns
65
0.7
60
2
-0.5
5
T
j
= 25
°
C (6)
12
≤
V
i
≤
25V
T
MIN
≤
T
amb
≤
T
MAX
(2)
V
PIN4
Peak to Peak
ERROR AMP SECTION
V
PIN1
= 2.5V
2.45 2.50 2.55 2.42 2.50 2.58
-0.3
90
1
70
6
-0.8
6
0.7
1.1
-1
65
0.7
60
2
-0.5
5
-0.3
90
1
70
6
-0.8
6
0.7
1.1
-2
V
µ
A
dB
MHz
dB
V
mA
V
V
47
52
0.2
5
1.7
57
1
47
52
0.2
5
1.7
57
1
KHz
%
%
V
T
j
= 25
°
C I
o
= 1mA
12V
≤
V
i
≤
25V
1
≤
I
o
≤
20mA
(Note 2)
Line, Load, Temperature (2)
10Hz
≤
f
≤
10KHz T
j
= 25°C
(2)
T
amb
= 125
°
C, 1000Hrs (2)
-30
4.9
50
5
25
-30
4.95 5.00 5.05 4.90 5.00 5.10
6
6
0.2
20
25
0.4
5.1
4.82
50
5
25
6
6
0.2
20
25
0.4
5.18
V
mV
mV
mV/°C
V
µV
mV
mA
UC284X
UC384X
Uni t
Min. T yp. Max. Min. Typ . Max.
-100 -180
-100 -180
3/11
UC2842/3/4/5-UC3842/3/4/5
ELECTRICAL CHARACTERISTICS
(continued)
Symbo l
Parameter
T est Cond ition s
UC284X
UC384X
Min. T yp. Max. Min. T yp. Max.
15
7.8
9
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
11.5
8.2
Unit
UNDER-VOLTAGE LOCKOUT SECTION
Start Threshold
X842/4
X843/5
Min Operating Voltage
After Turn-on
X842/4
X843/5
PWM SECTION
Maximum Duty Cycle
X842/3
X844/5
Minimum Duty Cycle
TOTAL STANDBY CURRENT
I
st
I
i
V
iz
Start-up Current
Operating Supply Current
Zener Voltage
V
PIN2
= V
PIN3
= 0V
I
i
= 25mA
0.5
11
34
1
20
0.5
11
34
1
20
mA
mA
V
93
46
97
48
100
50
0
93
47
97
48
100
50
0
%
%
%
V
V
V
V
N otes :
2. These parameters, although guaranteed, are not 100% tested in production.
3. Parameter measured at trip point of latch with V
PIN2
= 0.
4. Gain defined as :
∆
V
PIN1
A=
; 0
≤
V
PIN3
≤
0.8 V
∆
V
PIN3
5. Adjust V
i
above the start threshold before setting at 15 V.
6. Output frequency equals oscillator frequency for the UC3842 and UC3843.
Output frequency is one half oscillator frequency for the UC3844 and UC3845.
4/11
UC2842/3/4/5-UC3842/3/4/5
Figure 1 :
Error Amp Configuration.
Error amp can source or
sink up to 0.5mA
Figure 2 :
Under Voltage Lockout.
During Under-Voltage Lockout, the output driver is
biased to sink minor amounts of current. Pin 6
should be shunted to groundwith a bleederresistor
Figure 3 :
Current Sense Circuit .
to preventactivating the power switch with extrane-
ous leakage currents.
Peak current (i
s
) is determined by the formula
1.0 V
I
S max
≈
R
S
A small RC filter may be required to suppress switch transients.
5/11
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