UC3844A High Performance
Current Mode Controller
The UC3844A 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.
This integrated circuit features 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 deadtimes to be programmed for 50%
to 70%.
This device is available in an 8–pin dual–in–
line plastic package as well as the 14–pin plastic sur-
face mount (SOP–14). The SOP–14 package has sepa-
rate power and ground pins for the totem pole output
stage.
The UC3844A has UVLO thresholds of
16V (on) and 10V (off), Ideally suited for off-line
converters.
l
l
l
l
l
l
l
l
Output Deadtime Adjustable from 50% to 70%
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
CD SUFFIX
PLASTIC PACKAGE
8 DIP
D8 SUFFIX
PLASTIC PACKAGE
8 SOP
CS SUFFIX
PLASTIC PACKAGE
SOP-14
SIMPLIFIED BLOCK DIAGRAM
PIN CONNECTIONS
Pin numbers adjacent to terminals are for the D suffix 8-DIP package.
Pin numbers in parenthesis are for the S suffix SOP–14 package.
NOTES:
1. Maximum Package power dissipation limits must be observed.
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, T
high
= +70°C.
4. This parameter is measured at the latch trip point with V
FB
= 0V.
5. Comparator gain is defined as: A
V
∆V
Output Compensation
∆V
Current Sense Input
UC3844A High Performance
Current Mode Controller
ABSOLUTE MAXIMUM RATINGS
Item
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
CS, D8 Suffix, SOP-14, SOP-8 Package
Maximum Power Dissipation
Thermal Resistance, Junction to Air
CD Suffix, 8-DIP Package
Maximum Power Dissipation
Thermal Resistance, Junction to Air
Operating Ambient Temperature Range
Operating Junction Temperature
Storage Temperature Range
Symbol
(I
CC
+I
Z
)
I
O
W
V
in
I
O
Rating
30
1.0
5.0
-0.3 to +5.5
10
Unit
mA
A
µJ
V
mA
P
D
R
θJA
P
D
R
θJA
T
A
T
J
T
S
862
145
1.25
100
0 to 70
150
-65 to 150
o
mW
C/W
W
C/W
o
o
o
o
C
C
C
ELECTRICAL CHARACTERISTICS
V
CC
= 15V (Note 2), R
T
= 10k, CT = 3.3nF, T
A
= 0 to 70
o
C (Note 3) unless otherwise noted.
REFERENCE SECTION
Item
Symbol
o
Reference Output Voltage (I
O
= 1.0mA, T
J
= 25 C)
V
REF
Line Regulation (V
CC
= 12V to 25V)
Reg
line
Load Regulation (I
O
= 1.0mA to 20mA)
Reg
load
Temperature Stability
T
S
Total Output Variation over Line, Load, Temp.
V
REF
o
Output Noise Voltage (f = 10Hz to 10kHz, T
J
= 25 C)
V
n
o
Long Term Stability (T
A
= 125 C for 1000 Hours)
S
Output Short Circuit Current
ISC
OSCILLATOR SECTION
Frequency
f
OSC
o
T
J
= 25 C
T
A
= 0 to 70
o
C
Frequency Change with Voltage (V
CC
= 12V to 25V)
∆f
OSC
/∆V
Frequency Change with Temperature
∆f
OSC
/∆T
Oscillator Voltage Swing (Peak-to-Peak)
V
OSC
Discharge Current (V
OSC
= 2.0V)
I
dischg
o
T
J
= 25 C
Min Typ
4.9
5.0
---
2.0
---
3.0
---
0.2
4.82 ---
---
50
---
5.0
-30 -85
Max
5.1
20
25
---
5.18
---
---
-180
Unit
V
m
V
m
V
mV/
o
C
V
µV
m
V
mA
V
47
46
---
---
---
---
52
---
0.2
5.0
1.6
10.8
57
60
1.0
---
---
---
%
%
V
mA
UC3844A High Performance
Current Mode Controller
ELECTRICAL CHARACTERISTICS
ERROR AMPLIFIER SECTION
Item
Symbol
Voltage Feedback Input (V
O
= 2.5V)
V
FB
I
IB
Input Bias Current (V
FB
= 2.7V)
Open Loop Voltage Gain (V
O
= 2.0V to 4.0V)
A
VOL
o
Unity Gain Bandwidth (T
J
= 25 C)
BW
Power Supply Rejection Ratio (V
CC
= 12V to 25V)
PSRR
Output Current
Sink (V
O
= 1.1V, V
FB
= 2.7V)
I
Sink
Source (V
O
= 5.0V, V
FB
= 2.3V)
I
Source
Output Voltage Swing
High State (R
L
= 15k to GND, V
FB
= 2.3V)
V
OH
Low State (R
L
= 15k to V
REF
, V
FB
= 2.3V)
V
OL
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 4 & 5)
A
V
Maximum Current Sense Input Threshold (Note 4)
V
TH
Power Supply Rejection Ratio (V
CC
= 12V to 25V)
PSRR
Input Bias Current
I
IB
Propagation Delay (Current Sense Input to Output) t
PLH(in/out)
OUTPUT SECTION
Output Voltage
Low State
(I
Sink
= 20mA)
V
OL
(I
Sink
= 200mA)
High State
(I
Sink
= 20mA)
V
OH
(I
Sink
= 200mA)
Output Voltage with UVLO Activated
V
OL(UVLO)
(V
CC
= 6.0V, I
Sink
= 1.0mA)
Output Voltage Rise Time (C
L
= 1.0nF, T
J
= 25
o
C)
t
r
o
Output Voltage Fall Time (C
L
= 1.0nF, T
J
= 25 C)
t
f
UNDERVOLTAGE LOCKOUT SECTION
Startup Threshold
V
th
Minimum Operating Voltage After Turn-On
V
CC(min)
PWM SECTION
Duty Cycle
Max.
DC
max
Min.
DC
min
TOTAL DEVICE
Power Supply Current (V
CC
= 14V) (Note 2)
I
CC
Startup
Operating
Power Supply Zener Voltage
V
Z
Min Typ
2.42 2.5
---
-0.1
65
90
0.7
1.0
60
70
2.0
-0.5
5.0
---
2.85
0.9
---
---
---
12
-1.0
6.2
0.8
3.0
1.0
70
-2.0
150
Max
2.58
-2.0
---
---
---
---
---
V
---
1.1
3.15
1.1
---
-10
300
V/V
V
dB
µA
ns
V
---
---
13
12
---
---
---
14.5
8.5
47
---
0.1
1.6
13.5
13.4
0.1
50
50
16
10
48
---
0.4
2.2
---
---
V
1.1
150
150
17.5
11.5
50
0
ns
ns
V
V
%
Unit
V
µA
dB
MHz
dB
mA
mA
---
---
30
0.17
12
36
0.3
17
---
V
UC3844A High Performance
Current Mode Controller
FIGURE 1 - TIMING RESISTOR versus
OSCILLATOR FREQUENCY
PERCENT OUTPUT DEADTIME
OSCILLATOR FREQUENCY (Hz)
FIGURE 3 - ERROR AMP SMALL SIGNAL
TRANSIENT RESPONSE
FIGURE 2 - OUTPUT DEADTIME versus
OSCILLATOR FREQUENCY
TIMING RESISTOR (kΩ)
OSCILLATOR FREQUENCY (Hz)
FIGURE 4 - ERROR AMP LARGE SIGNAL
TRANSIENT RESPONSE
FIGURE 5 - ERROR AMP OPEN-LOOP GAIN
AND PHASE versus FREQUENCY
OPEN-LOOP VOLTAGE GAIN (dB)
EXCESS PHASE (DEGREES)
FREQUENCY (Hz)
FIGURE 6 - CURRENT SENSE INPUT THRESHOLD
versus ERROR AMP OUTPUT VOLTAGE
CURRENT SENSE INPUT
THRESHOLD (V)
ERROR AMP OUTPUT VOLTAGE (V)
UC3844A High Performance
Current Mode Controller
REFERENCE VOLTAGE CHANGE (mV)
FIGURE 7 - REFERENCE VOLTAGE CHANGE
versus SOURCE CURRENT
FIGURE 8 - REFERENCE SHORT CIRCUIT CURRENT
versus TEMPERATURE
REFERENCE SHORT CIRCUIT
CURRENT (mA)
REFERENCE SOURCE CURRENT (mA)
OUTPUT VOLTAGE CHANGE (2.0mV/DIV)
OUTPUT VOLTAGE CHANGE (2.0mV/DIV)
FIGURE 9 - REFERENCE LOAD REGULATION
AMBIENT TEMPERATURE (
o
C)
FIGURE 10 - REFERENCE LINE REGULATION
2.0 mS/DIV
FIGURE 11 - OUTPUT SATURATION VOLTAGE
versus LOAD CURRENT
2.0 mS/DIV
FIGURE 12 - OUTPUT WAVEFORM
OUTPUT SATURATION VOLTAGE (V)
OUTPUT LOAD CURRENT (mA)
DSP and ARM Processors
京公网安备 11010802033920号
EEWORLD
