UC3844, UC3845, UC2844,
UC2845
High Performance
Current Mode Controllers
The UC3844, UC3845 series are high performance fixed frequency
current mode controllers. They 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 an oscillator, 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, a latch for single pulse metering, and a flip−flop which
blanks the output off every other oscillator cycle, allowing output dead
times to be programmed for 50% to 70%.
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 UCX844 has UVLO thresholds of 16 V (on) and 10 V (off),
ideally suited for off−line converters. The UCX845 is tailored for
lower voltage applications having UVLO thresholds of 8.5 V (on) and
7.6 V (off).
Features
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PDIP−8
N SUFFIX
CASE 626
1
14
1
8
1
SOIC−14
D SUFFIX
CASE 751A
SOIC−8
D1 SUFFIX
CASE 751A
8
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
•
•
•
•
•
•
•
•
•
•
Current Mode Operation to 500 kHz Output Switching Frequency
Output Deadtime Adjustable from 50% to 70%
Automatic Feed Forward Compensation
Latching PWM for Cycle−By−Cycle Current Limiting
Internally Trimmed Reference with Undervoltage Lockout
High Current Totem Pole Output
Input Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
Direct Interface with ON Semiconductor SENSEFETt Products
Pb−Free Packages are Available
V
CC
V
ref
8(14)
R
R
R
T
C
T
4(7)
V
ref
Undervoltage
Lockout
Oscillator
Flip
Flop
&
Latching
PWM
5.0V
Reference
7(12)
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
V
CC
Undervoltage
Lockout
V
C
7(11)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 14 of this data sheet.
Output
6(10)
PWR GND
5(8)
Current
Sense
3(5)
Voltage
Feedback
2(3)
1(1)
Output
Comp.
+
−
DEVICE MARKING INFORMATION
See general marking information in the device marking
section on page page 14 of this data sheet.
Error
Amplifier
GND 5(9)
Pin numbers in parenthesis are for the D suffix SOIC−14 package.
Figure 1. Simplified Block Diagram
©
Semiconductor Components Industries, LLC, 2006
July, 2006
−
Rev. 7
1
Publication Order Number:
UC3844/D
UC3844, UC3845, UC2844, UC2845
MAXIMUM RATINGS
Rating
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, Case 751A
Maximum Power Dissipation @ T
A
= 25°C
Thermal Resistance Junction−to−Air
N Suffix, Plastic Package, Case 626
Maximum Power Dissipation @ T
A
= 25°C
Thermal Resistance Junction−to−Air
Operating Junction Temperature
Operating Ambient Temperature
UC3844, UC3845
UC2844, UC2845
Storage Temperature Range
Symbol
(I
CC
+ I
Z
)
I
O
W
V
in
I
O
Value
30
1.0
5.0
−
0.3 to + 5.5
10
Unit
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
−
65 to + 150
mW
°C/W
W
°C/W
°C
°C
T
stg
°C
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
1. Maximum Package power dissipation limits must be observed.
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.)
UC284X
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 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)
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)
V
FB
I
IB
A
VOL
2.45
−
65
2.5
−0.1
90
2.55
−1.0
−
2.42
−
65
2.5
−0.1
90
2.58
−2.0
−
V
mA
dB
f
osc
47
46
−
−
−
−
52
−
0.2
5.0
1.6
10.8
57
60
1.0
−
−
−
47
46
−
−
−
−
52
−
0.2
5.0
1.6
10.8
57
60
1.0
−
−
−
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
UC384X
Typ
Max
Unit
Df
osc/
D
V
Df
osc/
D
T
V
osc
I
dischg
%
%
V
mA
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
high
= +70°C for UC3844, UC3845
T
low
= 0°C for UC3844, UC3845
−25°C
for UC2844, UC2845
+85°C for UC2844, UC2845
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UC3844, UC3845, UC2844, UC2845
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.)
UC284X
Characteristics
ERROR AMPLIFIER SECTION (continued)
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)
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 V 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)
(I
Sink
= 200 mA)
High State (I
Sink
= 20 mA)
(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
UCX844
UCX845
Minimum Operating Voltage After Turn−On
UCX844
UCX845
PWM SECTION
Duty Cycle
Maximum
Minimum
TOTAL DEVICE
Power Supply Current (Note 4)
Startup:
(V
CC
= 6.5 V for UCX845A,
(V
CC
14 V for UCX844) 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
46
−
48
−
50
0
47
−
48
−
50
0
V
th
V
15
7.8
9.0
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
9.0
V
11.5
8.2
V
V
OL
V
OH
V
OL(UVLO)
t
r
t
f
−
−
12
12
−
−
−
0.1
1.6
13.5
13.4
0.1
50
50
0.4
2.2
−
−
1.1
150
150
−
−
13
12
−
−
−
0.1
1.6
13.5
13.4
0.1
50
50
0.4
2.2
−
−
V
1.1
150
150
ns
ns
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
BW
PSRR
I
Sink
I
Source
V
OH
V
OL
0.7
60
2.0
−0.5
5.0
−
1.0
70
12
−1.0
6.2
0.8
−
−
−
−
−
1.1
0.7
60
2.0
−0.5
5.0
−
1.0
70
12
−1.0
6.2
0.8
−
−
−
−
V
−
1.1
MHz
dB
mA
Symbol
Min
Typ
Max
Min
UC384X
Typ
Max
Unit
V
CC(min)
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
high
= +70°C for UC3844, UC3845
T
low
= 0°C for UC3844, UC3845
−25°C
for UC2844, UC2845
+85°C for UC2844, UC2845
6. This parameter is measured at the latch trip point with V
FB
= 0 V.
7. Comparator gain is defined as: A
V
DV
Output Compensation
DV
Current Sense Input
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UC3844, UC3845, UC2844, UC2845
% DT, PERCENT OUTPUT DEADTIME
10
0
50
20
10
5.0
2.0
75
V
CC
= 15 V
T
A
= 25°C
RT, TIMING RESISTOR (k
Ω
)
70
65
C
T
= 10 nF
5.0 nF
1.0 nF
2.0 nF
60
55
50
10 k
500
pF
NOTE: Output switches
at one−half the oscillator
frequency.
1.0
10 k
100
pF
200
pF
20 k
50 k
100 k
200 k
500 k
1.0 M
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
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
1.0
ms/DIV
Figure 4. Error Amp Small Signal
Transient Response
Figure 5. Error Amp Large Signal
Transient Response
A VOL , OPEN LOOP VOLTAGE GAIN (dB)
100
80
Gain
60
40
Phase
20
0
V
CC
= 15 V
V
O
= 2.0 V to 4.0 V
R
L
= 100 K
T
A
= 25°C
Vth, CURRENT SENSE INPUT THRESHOLD (V)
0
30
60
90
120
150
φ
EXCESS PHASE (DEGREES)
,
1.2
V
CC
= 15 V
1.0
0.8
0.6
T
A
= 125°C
0.4
0.2
0
T
A
= −55°C
T
A
= 25°C
− 20
10
100
1.0 k
10 k
100 k
1.0 M
180
10 M
0
f, FREQUENCY (Hz)
2.0
4.0
6.0
V
O
, ERROR AMP OUTPUT VOLTAGE (V)
8.0
Figure 6. Error Amp Open Loop Gain and
Phase versus Frequency
Figure 7. Current Sense Input Threshold
versus Error Amp Output Voltage
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200 mV/DIV
UC3844, UC3845, UC2844, UC2845
Δ
V ref , REFERENCE VOLTAGE CHANGE (mV)
0
V
CC
= 15 V
, REFERENCE SHORT CIRCUIT CURRENT (mA)
SC
110
V
CC
= 15 V
R
L
≤
0.1
W
90
−4.0
−8.0
−12
−16
−20
−24
T
A
= 125°C
T
A
= 25°C
70
T
A
= −55°C
0
20
40
60
80
100
120
50
−55
−25
0
25
50
75
100
125
I
ref
, REFERENCE SOURCE CURRENT (mA)
T
A
, AMBIENT TEMPERATURE (°C)
Figure 8. Reference Voltage Change
versus Source Current
I
Figure 9. Reference Short Circuit Current
versus Temperature
Δ
V , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)
V
CC
= 15 V
I
O
= 1.0 mA to 20 mA
T
A
= 25°C
Δ
V , OUTPUT VOLTAGE CHANGE (2.0 mV/DIV)
V
CC
= 12 V to 25 V
T
A
= 25°C
O
O
2.0 ms/DIV
2.0 ms/DIV
Figure 10. Reference Load Regulation
Figure 11. Reference Line Regulation
V sat , OUTPUT SATURATION VOLTAGE (V)
0
V
CC
−1.0
−2.0
Source Saturation
(Load to Ground)
T
A
= 25°C
T
A
= −55°C
V
CC
= 15 V
80
ms
Pulsed Load
120 Hz Rate
90%
V
CC
= 15 V
C
L
= 1.0 nF
T
A
= 25°C
3.0
T
A
= −55°C
2.0
1.0
0
0
200
Sink Saturation
(Load to V
CC
)
T
A
= 25°C
10%
GN
D
400
600
800
50 ns/DIV
I
O
, OUTPUT LOAD CURRENT (mA)
Figure 12. Output Saturation Voltage
versus Load Current
Figure 13. Output Waveform
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