UC3842A, UC3843A,
UC2842A, UC2843A
High Performance
Current Mode Controllers
The UC3842A, UC3843A series of high performance fixed
frequency current mode controllers are specifically designed for
off−line and DC−to−DC converter applications offering the designer a
cost effective solution with minimal external components. These
integrated circuits feature a trimmed oscillator for precise duty cycle
control, a temperature compensated reference, high gain error
amplifier, current sensing comparator, and a high current totem pole
output ideally suited for driving a power MOSFET.
Also included are protective features consisting of input and
reference undervoltage lockouts each with hysteresis, cycle−by−cycle
current limiting, programmable output deadtime, and a latch for single
pulse metering.
These devices are available in an 8−pin dual−in−line plastic package
as well as the 14−pin plastic surface mount (SOIC−14). The SOIC−14
package has separate power and ground pins for the totem pole output
stage.
The UCX842A has UYLO thresholds of 16 V (on) and 10 V (off),
ideally suited for off−line converters. The UCX843A is tailored for
lower voltage applications having UVLO thresholds of 8.5 V (on) and
7.6 V (off).
Features
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8
1
PDIP−8
N SUFFIX
CASE 626
14
1
SOIC−14
D SUFFIX
CASE 751A
8
1
SOIC−8
D1 SUFFIX
CASE 751
PIN CONNECTIONS
Compensation 1
Voltage Feedback 2
Current Sense 3
R
T
/C
T
4
(Top View)
8
7
6
5
V
ref
V
CC
Output
GND
•
Trimmed Oscillator Discharge Current for Precise Duty Cycle
•
•
•
•
•
•
•
•
•
Control
Current Mode Operation to 500 kHz
Automatic Feed Forward Compensation
Latching PWM for Cycle−By−Cycle Current Limiting
Internally Trimmed Reference with Undervoltage Lockout
High Current Totem Pole Output
Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
Direct Interface with ON Semiconductor SENSEFET™ Products
Pb−Free Packages are Available
Compensation
NC
Voltage Feedback
NC
Current Sense
NC
R
T
/C
T
1
2
3
4
5
6
7
(Top View)
14 V
ref
13 NC
12 V
CC
11 V
C
10 Output
9
8
GND
Power Ground
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 15 of this data sheet.
DEVICE MARKING INFORMATION
See general marking information in the device marking
section on page 16 of this data sheet.
©
Semiconductor Components Industries, LLC, 2005
1
November, 2005 − Rev. 8
Publication Order Number:
UC3842A/D
UC3842A, UC3843A, UC2842A, UC2843A
V
CC
V
ref
8(14)
R
R
R
T
C
T
4(7)
Voltage
Feedback
Input
2(3)
Output
Compensation
1(1)
+
−
7(12)
5.0V
Reference
V
ref
Undervoltage
Lockout
Oscillator
Latching
PWM
Error
Amplifier
V
CC
Undervoltage
Lockout
V
C
7(11)
Output
6(10)
Power
Ground
5(8)
Current
Sense
3(5) Input
GND
5(9)
Pin numbers in parenthesis are for the D suffix SOIC−14 package.
Figure 1. Simplified Block Diagram
MAXIMUM RATINGS
Rating
Bias and Driver Voltages (Zero Series Impedance, see also Total Device spec)
Total Power Supply and Zener Current
Output Current, Source or Sink (Note 1)
Output Energy (Capacitive Load per Cycle)
Current Sense and Voltage Feedback Inputs
Error Amp Output Sink Current
Power Dissipation and Thermal Characteristics
D Suffix, Plastic Package
Maximum Power Dissipation @ T
A
= 25°C
Thermal Resistance, Junction−to−Air
N Suffix, Plastic Package
Maximum Power Dissipation @ T
A
= 25°C
Thermal Resistance, Junction−to−Air
Operating Junction Temperature
Operating Ambient Temperature
UC3842A, UC3843A
UC2842A, UC2843A
Storage Temperature Range
Symbol
V
CC
, V
C
(I
CC
+ I
Z
)
I
O
W
V
in
I
O
Value
30
30
1.0
5.0
− 0.3 to + 5.5
10
Unit
V
mA
A
mJ
V
mA
P
D
R
qJA
P
D
R
qJA
T
J
T
A
862
145
1.25
100
+ 150
0 to + 70
− 25 to + 85
mW
°C/W
W
°C/W
°C
°C
T
stg
− 65 to + 150
°C
Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit
values (not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied,
damage may occur and reliability may be affected.
1. Maximum Package power dissipation limits must be observed.
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2
UC3842A, UC3843A, UC2842A, UC2843A
ELECTRICAL CHARACTERISTICS
(V
CC
= 15 V, [Note 2], R
T
= 10 k, C
T
= 3.3 nF, T
A
= T
low
to T
high
[Note 3],
unless otherwise noted.)
UC284XA
Characteristics
REFERENCE SECTION
Reference Output Voltage (I
O
= 1.0 mA, T
J
= 25°C)
Line Regulation (V
CC
= 12 V to 25 V)
Load Regulation (I
O
= 1.0 mA to 20 mA)
Temperature Stability
Total Output Variation over Line, Load, Temperature
Output Noise Voltage (f = 10 Hz to 10 kHz,
T
J
= 25°C)
Long Term Stability (T
A
= 125°C for 1000 Hours)
Output Short Circuit Current
OSCILLATOR SECTION
Frequency
T
J
= 25°C
T
A
= T
low
to T
high
Frequency Change with Voltage (V
CC
= 12 V to 25 V)
Frequency Change with Temperature
T
A
= T
low
to T
high
Oscillator Voltage Swing (Peak−to−Peak)
Discharge Current (V
osc
= 2.0 V)
T
J
= 25°C
T
A
= T
low
to T
high
ERROR AMPLIFIER SECTION
Voltage Feedback Input (V
O
= 2.5 V)
Input Bias Current (V
FB
= 2.7 V)
Open Loop Voltage Gain (V
O
= 2.0 V to 4.0 V)
Unity Gain Bandwidth (T
J
= 25°C)
Power Supply Rejection Ratio (V
CC
= 12 V to 25 V)
Output Current
Sink (V
O
= 1.1 V, V
FB
= 2.7 V)
Source (V
O
= 5.0 V, V
FB
= 2.3 V)
Output Voltage Swing
High State (R
L
= 15 k to ground, V
FB
= 2.3 V)
Low State (R
L
= 15 k to V
ref
, V
FB
= 2.7 V)
V
FB
I
IB
A
VOL
BW
PSRR
I
Sink
I
Source
V
OH
V
OL
2.45
−
65
0.7
60
2.0
−0.5
2.5
−0.1
90
1.0
70
12
−1.0
2.55
−1.0
−
−
−
−
−
2.42
−
65
0.7
60
2.0
−0.5
2.5
−0.1
90
1.0
70
12
−1.0
2.58
−2.0
−
−
−
−
−
V
5.0
−
6.2
0.8
−
1.1
5.0
−
6.2
0.8
−
1.1
V
mA
dB
MHz
dB
mA
f
osc
47
46
Df
osc/
D
V
Df
osc/
D
T
V
osc
I
dischg
7.5
7.2
8.4
−
9.3
9.5
7.5
7.2
8.4
−
9.3
9.5
−
−
−
52
−
0.2
5.0
1.6
57
60
1.0
−
−
47
46
−
−
−
52
−
0.2
5.0
1.6
57
60
1.0
−
−
%
%
V
mA
kHz
V
ref
Reg
line
Reg
load
T
S
V
ref
V
n
S
I
SC
4.95
−
−
−
4.9
−
−
− 30
5.0
2.0
3.0
0.2
−
50
5.0
− 85
5.05
20
25
−
5.1
−
−
− 180
4.9
−
−
−
4.82
−
−
− 30
5.0
2.0
3.0
0.2
−
50
5.0
− 85
5.1
20
25
−
5.18
−
−
− 180
V
mV
mV
mV/°C
V
mV
mV
mA
Symbol
Min
Typ
Max
Min
UC384XA
Typ
Max
Unit
2. Adjust V
CC
above the Startup threshold before setting to 15 V.
3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
T
low
= 0°C for UC3842A, UC3843A
T
high
= +70°C for UC3842A, UC3843A
−25°C for UC2842A, UC2843A
+85°C for UC2842A, UC2843A
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3
UC3842A, UC3843A, UC2842A, UC2843A
ELECTRICAL CHARACTERISTICS
(V
CC
= 15 V, [Note 4], R
T
= 10 k, C
T
= 3.3 nF, T
A
= T
low
to T
high
[Note 5],
unless otherwise noted.)
UC284XA
Characteristics
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 6 & 7)
Maximum Current Sense Input Threshold (Note 6)
Power Supply Rejection Ratio
V
CC
= 12 to 25 V (Note 6)
Input Bias Current
Propagation Delay (Current Sense Input to Output)
OUTPUT SECTION
Output Voltage
Low State (I
Sink
= 20 mA)
Low State
(I
Sink
= 200 mA)
High State (I
Sink
= 20 mA)
High State
(I
Sink
= 200 mA)
Output Voltage with UVLO Activated
V
CC
= 6.0 V, I
Sink
= 1.0 mA
Output Voltage Rise Time (C
L
= 1.0 nF, T
J
= 25°C)
Output Voltage Fall Time (C
L
= 1.0 nF, T
J
= 25°C)
UNDERVOLTAGE LOCKOUT SECTION
Startup Threshold
UCX842A
UCX843A
Minimum Operating Voltage After Turn−On
UCX842A
UCX843A
PWM SECTION
Duty Cycle
Maximum
Minimum
TOTAL DEVICE
Power Supply Current (Note 4)
Startup:
(V
CC
= 6.5 V for UCX843A,
(V
CC
=
14 V for UCX842A) Operating
Power Supply Zener Voltage (I
CC
= 25 mA)
I
CC
−
−
V
Z
30
0.5
12
36
1.0
17
−
−
−
30
0.5
12
36
1.0
17
−
V
mA
%
DC
max
DC
min
94
−
96
−
−
0
94
−
96
−
−
0
V
th
15
7.8
V
CC(min)
9.0
7.0
10
7.6
11
8.2
8.5
7.0
10
7.6
11.5
8.2
16
8.4
17
9.0
14.5
7.8
16
8.4
17.5
9.0
V
V
V
V
OL
V
OH
V
OL(UVLO)
−
t
r
t
f
−
−
0.1
50
50
1.1
150
150
−
−
−
0.1
50
50
1.1
150
150
ns
ns
−
−
13
12
0.1
1.6
13.5
13.4
0.4
2.2
−
−
−
−
13
12
0.1
1.6
13.5
13.4
0.4
2.2
−
−
V
A
V
V
th
PSRR
−
I
IB
t
PLH(in/out)
−
−
70
−2.0
150
−
−10
300
−
−
−
70
−2.0
150
−
−10
300
mA
ns
2.85
0.9
3.0
1.0
3.15
1.1
2.85
0.9
3.0
1.0
3.15
1.1
V/V
V
dB
Symbol
Min
Typ
Max
Min
UC384XA
Typ
Max
Unit
4. Adjust V
CC
above the Startup threshold before setting to 15 V.
5. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
T
low
= 0°C for UC3842A, UC3843A
T
high
= +70°C for UC3842A, UC3843A
−25°C for UC2842A, UC2843A
+85°C for UC2842A, UC2843A
6. This parameter is measured at the latch trip point with V
FB
= 0 V.
DV
Output Compensation
7. Comparator gain is defined as: A
V
DV
Current Sense Input
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4
UC3842A, UC3843A, UC2842A, UC2843A
80
50
RT, TIMING RESISTOR (k
Ω
)
20
8.0
5.0
2.0
0.8
V
CC
= 15 V
T
A
= 25°C
10 k
20 k
50 k
100 k
200 k
500 k
1.0 M
100
% DT, PERCENT OUTPUT DEADTIME
50
20
10
5.0
2.0
1.0
V
CC
= 15 V
T
A
= 25°C
10 k
20 k
50 k
100 k
200 k
500 k
1.0 M
f
OSC
, OSCILLATOR FREQUENCY (Hz)
f
OSC
, OSCILLATOR FREQUENCY (Hz)
Figure 2. Timing Resistor versus
Oscillator Frequency
Figure 3. Output Deadtime versus
Oscillator Frequency
9.0
I dischg , DISCHARGE CURRENT (mA)
V
CC
= 15 V
V
OSC
= 2.0 V
8.5
Dmax , MAXIMUM OUTPUT DUTY CYCLE (%)
100
90
80
70
60
50
40
800
V
CC
= 15 V
C
T
= 3.3 nF
T
A
= 25°C
I
dischg
= 7.2 mA
8.0
7.5
I
dischg
= 9.5 mA
1.0 k
2.0 k
3.0 k
4.0 k
6.0 k
8.0 k
7.0
−55
−25
0
25
50
75
T
A
, AMBIENT TEMPERATURE (°C)
100
125
R
T
, TIMING RESISTOR (W)
Figure 4. Oscillator Discharge Current
versus Temperature
Figure 5. Maximum Output Duty Cycle
versus Timing Resistor
2.55 V
V
CC
= 15 V
A
V
= −1.0
T
A
= 25°C
3.0 V
V
CC
= 15 V
A
V
= −1.0
T
A
= 25°C
20 mV/DIV
2.5 V
2.5 V
2.45 V
0.5
ms/DIV
2.0 V
0.1
ms/DIV
Figure 6. Error Amp Small Signal
Transient Response
Figure 7. Error Amp Large Signal
Transient Response
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5
200 mV/DIV
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