UC1842A/3A/4A/5A
UC2842A/3A/4A/5A
UC3842A/3A/4A/5A
Current Mode PWM Controller
FEATURES
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Optimized for Off-line and DC to DC
Converters
Low Start Up Current (<0.5mA)
Trimmed Oscillator Discharge Current
Automatic Feed Forward Compensation
Pulse-by-Pulse Current Limiting
Enhanced Load Response Characteristics
Under-Voltage Lockout With Hysteresis
Double Pulse Suppression
Part #
UVLO On
16.0V
8.5V
16.0V
8.5V
UVLO Off
10.0V
7.9V
10.0V
7.9V
Maximum Duty
Cycle
<100%
<100%
<50%
<50%
DESCRIPTION
The UC1842A/3A/4A/5A family of control ICs is a pin for pin compat-
ible improved version of the UC3842/3/4/5 family. Providing the nec-
essary features to control current mode switched mode power
supplies, this family has the following improved features. Start up cur-
rent is guaranteed to be less than 0.5mA. Oscillator discharge is
trimmed to 8.3mA. During under voltage lockout, the output stage can
sink at least 10mA at less than 1.2V for V
CC
over 5V.
The difference between members of this family are shown in the table
below.
High Current Totem Pole Output
Internally Trimmed Bandgap Reference
500kHz Operation
Low R
O
Error Amp
UC1842A
UC1843A
UC1844A
UC1845A
BLOCK DIAGRAM
Note 1: A/B A = DIL-8 Pin Number. B = SO-14 Pin Number.
Note 2: Toggle flip flop used only in 1844A and 1845A.
9/94
UC1842A/3A/4A/5A
UC2842A/3A/4A/5A
UC3842A/3A/4A/5A
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage (Low Impedance Source) . . . . . . . . . . . . . . 30V
Supply Voltage (I
CC
mA). . . . . . . . . . . . . . . . . . . . . Self Limiting
Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
±
1A
Output Energy (Capacitive Load) . . . . . . . . . . . . . . . . . . . . . 5µJ
Analog Inputs (Pins 2, 3) . . . . . . . . . . . . . . . . . . -0.3V to +6.3V
Error Amp Output Sink Current . . . . . . . . . . . . . . . . . . . . 10mA
Power Dissipation at T
A
≤
25°C (DIL-8) . . . . . . . . . . . . . . . . 1W
Storage Temperature Range . . . . . . . . . . . . . -65°C to +150°C
Lead Temperature (Soldering, 10 Seconds) . . . . . . . . . . 300°C
Note 1. All voltages are with respect to Ground, Pin 5. Currents
are positive into, negative out of the specified terminal. Consult
Packaging Section of Databook for thermal limitations and con-
siderations of packages. Pin numbers refer to DIL package only.
CONNECTION DIAGRAMS
DIL-8, SOIC-8 (TOP VIEW)
J or N, D8 Package
SOIC-14 (TOP VIEW)
D Package
PLCC-20, LCC-20
(TOP VIEW)
Q, L Packages
PACKAGE PIN FUNCTION
FUNCTION
PIN
N/C
1
Comp
2
N/C
3-4
V
FB
5
N/C
6
I
SENSE
7
N/C
8-9
R
T
/C
T
10
N/C
11
Pwr Gnd
12
Gnd
13
N/C
14
Output
15
N/C
16
V
C
17
V
CC
18
N/C
19
V
REF
20
UC184xA; -40°C
≤
T
A
≤
85°C for the UC284xA; 0
≤
T
A
≤
70°C for the UC384xA; V
CC
= 15V (Note 5); R
T
= 10k; C
T
= 3.3nF; T
A
= T
J
; Pin
numbers refer to DIL-8.
PARAMETER
Reference Section
Output Voltage
Line Regulation
Load Regulation
Temp. Stability
Total Output Variation
Output Noise Voltage
Long Term Stability
Output Short Circuit
Oscillator Section
Initial Accuracy
Voltage Stability
Temp. Stability
Amplitude
Discharge Current
TEST CONDITIONS
UC184xA\UC284xA
MIN. TYP. MAX.
4.95
5.00
6
6
0.2
5.05
20
25
0.4
5.1
UC384xA
UNITS
MIN. TYP. MAX.
4.90
5.00
6
6
0.2
5.10
20
25
0.4
5.18
V
mV
mV
mV/°C
V
µV
mV
mA
kHz
%
%
V
mA
mA
ELECTRICAL CHARACTERISTICS
Unless otherwise stated, these specifications apply for -55°C
≤
T
A
≤
125°C for the
T
J
= 25°C, I
O
= 1mA
12
≤
V
IN
≤
25V
1
≤
I
O
≤
20mA
(Note 2, Note 7)
Line, Load, Temp.
10Hz
≤
f
≤
10kHz
T
J
= 25°C (Note 2)
T
A
= 125°C, 1000Hrs. (Note 2)
4.9
50
5
-100
52
0.2
5
1.7
8.3
4.82
50
5
-100
52
0.2
5
1.7
8.3
-30
T
J
= 25°C (Note 6)
12
≤
V
CC
≤
25V
T
MIN
≤
T
A
≤
T
MAX
(Note 2)
V
PIN 4
peak to peak (Note 2)
T
J
= 25°C, V
PIN 4
= 2V (Note 8)
V
PIN 4
= 2V (Note 8)
47
25
-180
57
1
-30
47
25
-180
57
1
7.8
7.5
8.8
8.8
7.8
7.6
8.8
8.8
2
UC1842A/3A/4A/5A
UC2842A/3A/4A/5A
UC3842A/3A/4A/5A
ELECTRICAL CHARACTERISTICS (cont.)
Unless otherwise stated, these specifications apply for -55°C
≤
T
A
≤
125°C for
the UC184xA; -40°C
≤
T
A
≤
85°C for the UC284xA; 0
≤
T
A
≤
70°C for the UC384xA; V
CC
= 15V (Note 5); R
T
= 10k; C
T
= 3.3nF; T
A
= T
J
;
Pin numbers refer to DIL-8.
PARAMETER
Error Amp Section
Input Voltage
Input Bias Current
A
VOL
Unity Gain Bandwidth
PSRR
Output Sink Current
Output Source Current
V
OUT
High
V
OUT
Low
Current Sense Section
Gain
Maximum Input Signal
PSRR
Input Bias Current
Delay to Output
Output Section
Output Low Level
Output High Level
Rise Time
Fall Time
UVLO Saturation
Under-Voltage Lockout Section
Start Threshold
Min. Operation Voltage After
Turn On
PWM Section
Maximum Duty Cycle
Minimum Duty Cycle
Total Standby Current
Start-Up Current
Operating Supply Current
V
CC
Zener Voltage
TEST CONDITIONS
UC184xA\UC284xA
MIN. TYP. MAX.
2.45
65
0.7
60
2
-0.5
5
2.50
-0.3
90
1
70
6
-0.8
6
0.7
3
1
70
-2
150
0.1
15
13.5
13.5
50
50
0.7
16
8.4
10
7.6
96
48
2.55
-1
UC384xA
UNITS
MIN. TYP. MAX.
2.42
65
0.7
60
2
-0.5
5
1.1
3.15
1.1
-10
300
0.4
2.2
13
12
150
150
1.2
17
9.0
11
8.2
100
50
0
0.5
17
30
14.5
7.8
8.5
7.0
94
47
2.85
0.9
2.50
-0.3
90
1
70
6
-0.8
6
0.7
3
1
70
-2
150
0.1
15
13.5
13.5
50
50
0.7
16
8.4
10
7.6
96
48
2.58
-2
V
µA
dB
MHz
dB
mA
mA
V
V
V/V
V
dB
µA
ns
V
V
V
V
ns
ns
V
V
V
V
V
%
%
%
mA
mA
V
V
PIN 1
= 2.5V
2
≤
V
O
≤
4V
T
J
= 25°C (Note 2)
12
≤
V
CC
≤
25V
V
PIN 2
= 2.7V, V
PIN 1
= 1.1V
V
PIN 2
= 2.3V, V
PIN 1
= 5V
V
PIN 2
= 2.3V, R
L
= 15k to ground
V
PIN 2
= 2.7V, R
L
= 15k to Pin 8
(Note 3, Note 4)
V
PIN 1
= 5V (Note 3)
12
≤
V
CC
≤
25V (Note 3)
V
PIN 3
= 0 to 2V (Note 2)
I
SINK
= 20mA
I
SINK
= 200mA
I
SOURCE
= 20mA
I
SOURCE
= 200mA
T
J
= 25°C, C
L
= 1nF (Note 2)
T
J
= 25°C, C
L
= 1nF (Note 2)
V
CC
= 5V, I
SINK
= 10mA
x842A/4A
x843A/5A
x842A/4A
x843A/5A
x842A/3A
x844A/5A
1.1
3.15
1.1
-10
300
0.4
2.2
2.85
0.9
13
12
150
150
1.2
17.5
9.0
11.5
8.2
100
50
0
0.5
17
15
7.8
9
7.0
94
47
V
PIN 2
= V
PIN 3
= 0V
I
CC
= 25mA
30
0.3
11
34
0.3
11
34
Note 2: These parameters, although guaranteed, are not 100%
tested in production.
Note 3: Parameter measured at trip point of latch with V
PIN2
= 0.
∆
V
PIN 1
Note 4: Gain defined as: A
=
; 0
≤
V
PIN 3
≤
0.8V.
∆
V
PIN 3
Note 5: Adjust V
CC
above the start threshold before setting at
15V.
Note 6: Output frequency equals oscillator frequency for the
UC1842A and UC1843A. Output frequency is one half
oscillator frequency for the UC1844A and UC1845A.
Note 7: "Temperature stability, sometimes referred to as average
temperature coefficient, is described by the equation:
V
REF
(
max
)
−
V
REF
(
min
)
.
T
J
(
max
) −
T
J
(
min
)
V
REF
(max) and V
REF
(min) are the maximum & mini-
mum reference voltage measured over the appropriate
temperature range. Note that the extremes in voltage
do not necessarily occur at the extremes in tempera-
ture."
Note 8: This parameter is measured with R
T
= 10k
Ω
to V
REF
.
This contributes approximately 300
µ
A of current to the
measurement. The total current flowing into the R
T
/C
T
pin will be approximately 300
µ
A higher than the meas-
ured value.
Temp Stability
=
3
UC1842A/3A/4A/5A
UC2842A/3A/4A/5A
UC3842A/3A/4A/5A
Error Amp Configuration
Error Amp can Source and Sink up to 0.5mA, and Sink up to 2mA.
Under-Voltage Lockout
During UVLO, the Output is low.
Current Sense Circuit
Peak Current (I
S
) is Determined By The Formula
1.0V
I
SMAX
≈
R
S
A small RC filter may be required to suppress switch transients.
4
APPLICATIONS DATA (cont.)
Output Saturation Characteristics
UC1842A/3A/4A/5A
UC2842A/3A/4A/5A
UC3842A/3A/4A/5A
Error Amplifier Open-Loop Frequency Response
Oscillator Section
Oscillator Frequency vs Timing Resistance
Maximum Duty Cycle vs Timing Resistor
Open-Loop Laboratory Test Fixture
High peak currents associated with capacitive loads necessi-
tate careful grounding techniques. Timing and bypass capaci-
tors should be connected close to pin 5 in a single point
ground. The transistor and 5k potentiometer are used to sam-
ple the oscillator waveform and apply an adjustable ramp to
pin 3.
5
51mcu
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