UC3842A High Performance
Current Mode Controller
l
Trimmed Oscillator Discharge Current for Precise Duty
Cycle Control
l
Current Mode Operation to 500 kHz
l
Automatic Feed Forward Compensation
l
Latching PWM for CycleByCycle Current Limiting
l
Internally Trimmed Reference with Undervoltage Lockout
l
High Current Totem Pole Output
l
Undervoltage Lockout with Hysteresis
l
Low Startup and Operating Current
CS SUFFIX
PLASTIC PACKAGE
SOP-14
The UC3842A series of high performance
fixed frequency current mode controllers are
specifically designed for offline and dctodc
converter applications offering the designer a cost
effective solution with minimal external components.
This integrated circuit features 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, cyclebycycle current limiting,
programmable output deadtime, and a latch for single
pulse metering.
This device is available in an 8pin dualin
line plastic package as well as the 14pin plastic surface
mount (SO14). The SO14 package has separate
power and ground pins for the totem pole output
stage.
The UC3842A has UVLO thresholds of
16V(on) and 10V(off), ideally suited for offline
converters.
CD SUFFIX
PLASTIC PACKAGE
8 DIP
PIN CONNECTIONS
SIMPLIFIED BLOCK DIAGRAM
Pin numbers adjacent to terminals are for the D suffix 8-DIP package.
Pin numbers in parenthesis are for the S suffix SOP14 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
D8 SUFFIX
PLASTIC PACKAGE
8 SOP
4-12
UC3842A High Performance
Current Mode Controller
Total Power Supply and Zener Current
(I
CC
+I
Z
)
30
mA
Output Current, Source or Sink (Note 1)
I
O
1.0
A
Output Energy (Capacitive Load per Cycle)
W
5.0
J
Current Sense and Voltage Feedback Inputs
V
in
-0.3 to +5.5
V
Error Amp Output Sink Current
I
O
10
mA
Power Dissipation and Thermal Characteristics
CS, D8 Suffix, SOP-14, SOP-8 Package
Maximum Power Dissipation
P
D
862
mW
Thermal Resistance, Junction to Air
R
JA
145
o
C/W
CD Suffix, 8-DIP Package
Maximum Power Dissipation
P
D
1.25
W
Thermal Resistance, Junction to Air
R
JA
100
o
C/W
Operating Ambient Temperature Range
T
A
0 to 70
o
C
Operating Junction Temperature
T
J
150
o
C
Storage Temperature Range
T
S
-65 to 150
o
C
Item
Symbol
Rating
Unit
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
Item
Symbol
Min
Typ
Max
Unit
Reference Output Voltage (I
O
= 1.0mA, T
J
= 25
o
C)
V
REF
4.9
5.0
5.1
V
Line Regulation (V
CC
= 12V to 25V)
Reg
line
---
2.0
20
mV
Load Regulation (I
O
= 1.0mA to 20mA)
Reg
load
---
3.0
25
mV
Temperature Stability
T
S
---
0.2
---
mV/
o
C
Total Output Variation over Line, Load, Temp.
V
REF
4.82
---
5.18
V
Output Noise Voltage (f = 10Hz to 10kHz, T
J
= 25
o
C)
V
n
---
50
---
V
Long Term Stability (T
A
= 125
o
C for 1000 Hours)
S
---
5.0
---
mV
Output Short Circuit Current
ISC
-30
-85
-180
mA
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
Frequency
f
OSC
V
T
J
= 25
o
C
47
52
57
T
A
= 0 to 70
o
C
46
---
60
Frequency Change with Voltage (V
CC
= 12V to 25V)
f
OSC
/
V
---
0.2
1.0
%
Frequency Change with Temperature
f
OSC
/
T
---
5.0
---
%
Oscillator Voltage Swing (Peak-to-Peak)
V
OSC
---
1.6
---
V
Discharge Current (V
OSC
= 2.0V)
I
dischg
mA
T
J
= 25
o
C
7.5
8.4
9.3
T
A
= 0 to 70
o
C
7.2
---
9.5
OSCILLATOR SECTION
4-13
ELECTRICAL CHARACTERISTICS
Item
Symbol
Min
Typ
Max
Unit
Voltage Feedback Input (V
O
= 2.5V)
V
FB
2.42
2.5
2.58
V
Input Bias Current (V
FB
= 2.7V)
I
IB
---
-0.1
-2.0
A
Open Loop Voltage Gain (V
O
= 2.0V to 4.0V)
A
VOL
65
90
---
dB
Unity Gain Bandwidth (T
J
= 25
o
C)
BW
0.7
1.0
---
MHz
Power Supply Rejection Ratio (V
CC
= 12V to 25V)
PSRR
60
70
---
dB
Output Current
mA
Sink (V
O
= 1.1V, V
FB
= 2.7V)
I
Sink
2.0
12
---
Source (V
O
= 5.0V, V
FB
= 2.3V)
I
Source
-0.5
-1.0
---
Output Voltage Swing
V
High State (R
L
= 15k to GND, V
FB
= 2.3V)
V
OH
5.0
6.2
---
Low State (R
L
= 15k to V
REF
, V
FB
= 2.3V)
V
OL
---
0.8
1.1
ERROR AMPLIFIER SECTION
UC3842A High Performance
Current Mode Controller
Current Sense Input Voltage Gain (Notes 4 & 5)
A
V
2.85
3.0
3.15
V/V
Maximum Current Sense Input Threshold (Note 4)
V
TH
0.9
1.0
1.1
V
Power Supply Rejection Ratio (V
CC
= 12V to 25V)
PSRR
---
70
---
dB
Input Bias Current
I
IB
---
-2.0
-10
A
Propagation Delay (Current Sense Input to Output) t
PLH(in/out)
---
150
300
ns
CURRENT SENSE SECTION
Output Voltage
V
Low State
(I
Sink
= 20mA)
V
OL
---
0.1
0.4
(I
Sink
= 200mA)
---
1.6
2.2
High State
(I
Sink
= 20mA)
V
OH
13
13.5
---
(I
Sink
= 200mA)
12
13.4
---
Output Voltage with UVLO Activated
V
OL(UVLO)
V
(V
CC
= 6.0V, I
Sink
= 1.0mA)
---
0.1
1.1
Output Voltage Rise Time (C
L
= 1.0nF, T
J
= 25
o
C)
t
r
---
50
150
ns
Output Voltage Fall Time (C
L
= 1.0nF, T
J
= 25
o
C)
t
f
---
50
150
ns
OUTPUT SECTION
Startup Threshold
V
th
14.5
16
17.5
V
Minimum Operating Voltage After Turn-On
V
CC(min)
8.5
10
11.5
V
UNDERVOLTAGE LOCKOUT SECTION
Duty Cycle
Max.
DC
max
94
96
---
%
Min.
DC
min
---
---
0
PWM SECTION
Power Supply Current (V
CC
= 14V) (Note 2)
I
CC
mA
Startup
---
0.17
0.3
Operating
---
12
17
Power Supply Zener Voltage
V
Z
30
36
---
V
TOTAL DEVICE
4-14
UC3842A High Performance
Current Mode Controller
FIGURE 1 - TIMING RESISTOR versus
OSCILLATOR FREQUENCY
FIGURE 2 - OUTPUT DEADTIME versus
OSCILLATOR FREQUENCY
OSCILLATOR FREQUENCY (Hz)
TIMING RESISTOR (k
)
OSCILLATOR FREQUENCY (Hz)
PERCENT OUTPUT DEADTIME
FIGURE 4 - MAXIMUM OUTPUT DUTY CYCLE
versus TIMING RESISTOR
TIMING RESISTOR (
)
MAXIMUM OUTPUT DUTY CYCLE (%)
FIGURE 3 - OSCILLATOR DISCHARGE CURRENT
versus TEMPERATURE
AMBIENT TEMPERATURE (
o
C)
DISCHARGE CURRENT (mA)
FIGURE 5 - ERROR AMP SMALL SIGNAL
TRANSIENT RESPONSE
FIGURE 6 - ERROR AMP LARGE SIGNAL
TRANSIENT RESPONSE
4-15
UC3842A High Performance
Current Mode Controller
FIGURE 7 - ERROR AMP OPEN-LOOP GAIN
AND PHASE versus FREQUENCY
FREQUENCY (Hz)
OPEN-LOOP VOL
T
AGE GAIN (dB)
EXCESS PHASE (DEGREES)
FIGURE 8 - CURRENT SENSE INPUT THRESHOLD
versus ERROR AMP OUTPUT VOLTAGE
ERROR AMP OUTPUT VOLTAGE (V)
CURRENT SENSE INPUT
THRESHOLD (V)
FIGURE 10 - REFERENCE SHORT CIRCUIT CURRENT
versus TEMPERATURE
AMBIENT TEMPERATURE (
o
C)
REFERENCE SHOR
T CIRCUIT
CURRENT (mA)
FIGURE 9 - REFERENCE VOLTAGE CHANGE
versus SOURCE CURRENT
REFERENCE SOURCE CURRENT (mA)
REFERENCE VOL
T
AGE CHANGE (mV)
FIGURE 11 - REFERENCE LOAD REGULATION
2.0 mS/DIV
OUTPUT VOL
T
AGE CHANGE (2.0mV/DIV)
FIGURE 12 - REFERENCE LINE REGULATION
2.0 mS/DIV
OUTPUT VOL
T
AGE CHANGE (2.0mV/DIV)
4-16
PDF 
ZIP