UNISONIC TECHNOLOGIES CO., LTD
UC3844/45
HIGH PERFORMANCE
CURRENT MODE PWM
CONTROLLERS
DESCRIPTION
LINEAR INTEGRATED CIRCUIT
The UTC
UC3844/3845
are high performance fixed frequency
current mode controllers that specifically designed for Off-Line and
DC to DC converter applications with minimal external parts count.
The differences between
UC3844
and
UC3845
are the
maximum duty cycle ranges and under-voltage lockout thresholds.
The
UC3844
ideally suited to off-line applications with UVLO
thresholds of 16V
(ON)
and 10V
(OFF)
, and
UC3845
has UVLO
thresholds of 8.5V
(ON)
and 7.6V
(OFF)
for lower voltage applications.
FEATURES
* Operation output switching frequency up to 500 kHz
* Automatic feed forward compensation
* Latching PWM for cycle-by-cycle current limiting
* High current totem pole output
* Internally trimmed reference with under voltage lockout
* UVLO with hysteresis
* Low startup and operating current
ORDERING INFORMATION
Ordering Number
Lead Free
UC3844L-D08-T
-
UC3845L-D08-T
-
Halogen Free
UC3844G-D08-T
UC3844G-S08-R
UC3845G-D08-T
UC3845G-S08-R
Package
DIP-8
SOP-8
DIP-8
SOP-8
Packing
Tube
Tape Reel
Tube
Tape Reel
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UC3844/45
MARKING
UC3844
LINEAR INTEGRATED CIRCUIT
UC3845
DIP-8
SOP-8
PIN CONFIGURATION
PIN DESCRIPTION
PIN NAME
FUNCTION
Compensation Error amplifier output, this pin is made available for loop compensation.
Voltage Feedback, the inverting input of the Error Amplifier. It is normally connected to the
V
FB
switching power supply output through a resistor divider.
A voltage proportional to inductor current is connected to this input. The PWM uses this
I
SENSE
information to terminate the output switch conduction.
The Oscillator frequency and maximum output duty cycle are programmed by connecting
R
T
/C
T
resistor R
T
to Vref and capacitor C
T
to ground. Operation to 1 MHz is possible.
GND
Power ground.
This output directly drives the gate of a power MOSFET. Peak currents up to 1A are
Output
sourced and sunk by this pin. The output switches at one-half the oscillator frequency.
V
CC
Positive supply.
V
REF
Reference output, provides charging current for capacitor C
T
though resistor R
T
.
PIN NO
1
2
3
4
5
6
7
8
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UC3844/45
BLOCK DIAGRAM
LINEAR INTEGRATED CIRCUIT
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UC3844/45
ABSOLUTE MAXIMUM RATINGS
(T
A
=25°C)
LINEAR INTEGRATED CIRCUIT
PARAMETER
SYMBOL
RATINGS
UNIT
Current Sense and Voltage feedback Inputs
V
IN
-0.3 ~ +5.5
V
Total Power Supply and Zener Current
(I
CC
+I
Z
)
30
mA
Error Amp Output Sink Current
I
SINK
10
mA
Output Current, Source or Sink (Note 2)
I
OUT
1.0
A
Output Energy (Capacitive Load per cycle)
W
5.0
μJ
DIP-8
1250
Power Dissipation
P
D
mW
SOP-8
800
Junction Temperature
T
J
+150
°C
Operation Temperature
T
OPR
0 ~ 70
°C
Storage Temperature
T
STG
-65 ~ +150
°C
Note: 1. Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.
2. Maxmum package power dissipation limits must be observed.
THERMAL DATA
PARAMETER
SYMBOL
SOP-8
DIP-8
θ
JA
RATINGS
156
100
UNIT
°C/W
Junction to Ambient
ELECTRICAL CHARACTERISTICS
(T
A
=25°C, V
CC
=15V, R
T
=10k, C
T
=3.3nF, 0°C
≤
T
A
≤
70°C, unless otherwise specified)
PARAMETER
REFERENCE SECTION
Reference Output Voltage
Line Regulation
Load Regulation
Temperature Stability
Total Output Variation over Line,
Load, Temperature
Output Noise Voltage
Long Term Stability
Output Short Circuit Current
OSCILLATOR SECTION
Oscillator Voltage Swing
Discharge Current
Frequency
Frequency Change with Voltage
Frequency Change with Temperature
ERROR AMPLIFIER SECTION
Voltage Feedback Input
High
Output Voltage Swing
Low
Sink
Output Current
Source
Input Bias Current
Open Loop Voltage Gain
Power Supply Rejection Ratio
Unity Gain Bandwidth
SYMBOL
V
REF
△V
OUT
△V
OUT
t
S
V
REF
e
N
S
I
SC
V
OSC
I
DSG
f
OSC
f
OSC
/V
f
OSC
/T
V
FB
V
OH
V
OL
I
SINK
I
SOURCE
I
I(BIAS)
G
VO
PSRR
GB
W
f=10Hz ~ kHz, T
J
=25°C
T
A
=125°C for 1000 Hours
-30
4.82
50
5
-85
1.6
10.8
52
0.2
5.0
2.42
5.0
2.0
-0.5
65
60
0.7
2.50
6.2
0.8
12
-1.0
-0.1
90
70
1.0
TEST CONDITIONS
I
OUT
=1.0mA,T
J
=25°C
V
CC
=12V ~ 25V
I
OUT
=1.0mA ~ 20mA
MIN
4.9
TYP
5.0
2.0
3.0
0.2
MAX
5.1
20
25
5.18
UNIT
V
mV
mV
mV/°C
V
μV
mV
mA
V
mA
57
60
1.0
kHz
%
%
V
V
mA
-2.0
μA
dB
dB
MHz
-180
V
OSC
=2.0V, T
J
=25°C
T
J
=25°C
0°C
≤
T
A
≤
70°C
V
CC
=12V ~ 25V
0°C
≤
T
A
≤
70°C
V
OUT
=2.5V
R
L
=15k to ground, V
FB
=2.3V
R
L
=15k to V
REF
, V
FB
=2.7V
V
OUT
=1.1V, V
FB
=2.7V
V
OUT
=5.0V, V
FB
=2.3V
V
FB
=2.7V
V
OUT
=2.0V ~ 4.0V
V
CC
=12V ~ 25V
T
J
=25°C
47
46
2.58
1.1
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ELECTRICAL CHARACTERISTICS(Cont.)
SYMBOL
G
V
V
I(THR)
I
I(BIAS)
PSRR
t
PLH(IN/OUT)
V
OL
V
OH
PARAMETER
CURRENT SENSE SECTION
Current Sense Input Voltage Gain
(Note 2, 3)
Maximum Current Sense Input
Threshold (Note 2)
Input Bias Current
Power Supply Rejection Ratio
Propagation Delay
OUTPUT SECTION
Low
Output Voltage
High
LINEAR INTEGRATED CIRCUIT
TEST CONDITIONS
MIN
2.85
0.9
TYP
3.0
1.0
-2.0
70
150
0.1
1.6
13.5
13.4
0.1
50
50
MAX
3.15
1.1
-10
300
0.4
2.2
UNIT
V/V
V
μA
dB
ns
V
V
V
CC
=12V ~ 25V (Note 4)
Output Voltage with U
VLO
Activated
V
OL(UVLO)
1.1
V
Output Voltage Rise Time
t
R
150
ns
Output Voltage Fall Time
t
F
150
ns
UNDERVOLTAGE LOCKOUT SECTION
UC3844
14.5
16.0
17.5
Startup Threshold
V
THR
V
UC3845
7.8
8.4
9.0
UC3844
8.5
10.0
11.5
Minimum Operating
V
CC(MIN)
V
Voltage After Turn-On
UC3845
7.0
7.6
8.2
PWM SECTION
MAX
DC
MAX
47
48
50
%
Duty Cycle
MIN
DC
MIN
0
%
TOTAL DEVICE
Power Supply Zener Voltage
VZ
I
CC
=25mA
30
36
V
V
CC
=6.5V
UC3845
0.5
1.0
Power Supply Current
I
CC
mA
(Note 4)
UC3844
V
CC
=14V
12
17
Startup Current
I
START-UP
V
CC
=14V, UVLO Active
0.3
0.5
mA
Notes: 1. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient
as possible.
2. This parameter is measured at the latch trip point with V
FB
=0V.
3. Comparator gain is defined as:
V
Output Compensation
A
V
=
V
Current Sense Input
4. Adjust V
CC
above the startup threshold before setting to 15V.
I
SINK
=20mA
I
SINK
=200mA
I
SINK
=20mA
I
SINK
=200mA
V
CC
=6.0V, I
SINK
=1.0mA
C
L
=1.0nF,T
J
=25°C
C
L
=1.0nF,T
J
=25°C
13
12
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