CM3842/3843
C
URRENT
M
ODE
PWM C
ONTROLLER
GENERAL DESCRIPTION
FEATURES
Low Start-Up current ( typ. 200µA)
Optimized for Off-Line and DC-to-DC Converters
Maximum Duty Cycle
U.V.L.O. with Hysteresis
Operating Frequency Up to 500KHz
Internal Trimmed Bandgap Reference
High Current Totem Pole Output
Error Amplifier With Low Output Resistance
Available in 8-Pin Plastic DIP and Surface Mount
8-Pin S.O.I.C.
The CM3842/43 are fixed frequency current-mode PWM
!
controllers specially designed for OFF-Line switching
!
power supply and DC-to-DC converters with a minimum
!
number of external components. These devices feature
!
a trimmed oscillator for precise duty cycle control, a
!
temperature compensated reference, high gain error
!
amplifier, current sensing comparator, and high current
!
totem
pole output which is
suitable
for driving
!
!
MOSFETs.
The under voltage lock-out (U.V.L.O.) is designed to
operated with 200µA typ. start-up current, allowing an
efficient bootstrap supply voltage design. The U.V.L.O.
thresholds for the CM3842 are 16V (on) and 10V (off)
which
are
ideal
for
off-line
applications.
The
corresponding typical threshold for the CM3843 are
8.4V (on) and 7.6V (off). The CM3842/43 can operated
within 100% duty cycle.
APPLICATIONS
!
!
!
Off-line flyback or forward converters.
DC-to-DC buck or boost converter.
Monitor Power Supply
PIN CONFIGURATION
COMP
V
FB
I
SENSE
R
T
/C
T
V
REF
V
CC
OUTPUT
GND
8-Pin PDIP
(Top View)
AVAILABLE OPTIONS
Device
CM3842
CM3843
Start-UP
Voltage
16V
8.4V
Hysteresis Max. Duty Cycle
6V
0.8V
< 100%
< 100%
COMP
V
FB
I
SENSE
R
T
/C
T
V
REF
V
CC
OUTPUT
GND
8-Pin S.O.I.C.
(Top View)
2001/06/27
Advanced
Champion Microelectronic Corporation
Page 1
CM3842/3843
C
URRENT
M
ODE
PWM C
ONTROLLER
ORDERING INFORMATION
Part Number
CM3842/43CP
CM3842/43CS
Temperature Range
0℃ to 70℃
0℃ to 70℃
Package
8-Pin PDIP(P08)
8-Pin SOIC(S08)
BLOCK DIAGRAM
7
Internal
Bias
U.V.L.O.
5V
EN
V
REF
36V
V
CC
V
REF
8
5
GND
V
REF
Good Logic
7
Error Amp
2R
R
1
V
V
FB
2
Current
Sense
C
R
PWR
V
C
PWM
Latch
OUTPUT
COMP
1
S
6
3
T
Oscillator
CURRENT
SENSE
R
T
/C
T
4
5
PWR
GND
Note 1 :V
CC
and PWR V
C
are internally connected for 8 pin packages.
Note 2 :PWR GND and GND are internally connected for 8 pin packages.
Note 3 :U.V.L.O. is 16V for 3842 and 8.4V for 3843.
Note 4 :Hysteresis is 6V for 3842 and 0.8V for 3843.
2001/06/27
Advanced
Champion Microelectronic Corporation
Page 2
CM3842/3843
C
URRENT
M
ODE
PWM C
ONTROLLER
ABSOLUTE MAXIMUM RATINGS
Supply voltage, V
CC
Output current, I
O
Analog inputs, V
I
Error amp output sink current, I
SINK(EA)
Power dissipation (T
A
= 25 C), P
D
Maximum junction temperature T
J
Storage temperature range
Lead temperature (soldiering, 10 seconds)
Note 5:
Currents are positive into, negative out of the specified terminal.
O
35V
±
1A
-0.3V to 6.3V
10mA
1W
150 C
-65
O
C to 150
O
C
260 C
O
O
Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground.
THERMAL DATA
PDIP PACKAGE:
Thermal Resistance-Junction to Ambient,
θ
JA
SOIC PACKAGE:
Thermal Resistance-Junction to Ambient,
θ
JA
Junction Temperature Calculation:
T
J
= T
A
+ (P
D
× θ
JA
).
The
θ
JA
numbers are guidelines for the thermal performance of the device/pc-board system.
All of the above assume no ambient airflow.
165 C/W
O
95
O
C/W
2001/06/27
Advanced
Champion Microelectronic Corporation
Page 3
CM3842/3843
C
URRENT
M
ODE
PWM C
ONTROLLER
RECOMMENDED OPERATING CONDITIONS
Parameter
Symbol
Recommended Operating
Min.
Typ.
Max.
Units
Supply Voltage
Input Voltage
Output Voltage
Supply Current
Average Output Current
Reference Output Current
Timing Capacitor
Oscillator Frequency
Operating Free-air Temperature
V
CC
/ V
C
V
I
,R
T
/C
T
V
I
,I
SENSE
/V
FB
V
O
, Output
I
CC
I
O
I
O(REF)
C
T
f
OSC
T
A
0
1
100
0
0
30
5.5
30
25
200
-20
500
70
V
V
V
mA
mA
mA
nF
KHz
O
C
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, these specifications apply over the operating ambient temperature for CM384X with 0 C
≤
O
T
A
≤70
C; V
CC
= 15V(note 7); R
T
= 10K;C
T
= 3.3nF. Low duty cycle pulse testing techniques are used which
O
maintains junction and case temperatures equal to the ambient temperature.
CM384X
Parameter
Reference Section
Reference output Voltage
Line Regulation
Load Regulation
Short Ciruit Output Current
Oscillator Section
Oscillation Frequency
Frequency Change with Voltage
Frequency Change with Temperature
(note 8)
Peak-to-peak Amplitude At R
T
/C
T
Current Sense Section
Gain (note 9 & 10)
Maximum Input Signal (note 9)
Power Supply Rejection Ratio (note 9)
Input Bias Current
A
VOL
V
I(MAX)
PSRR
I
BIAS
COMP = 5V
12V
≤
V
CC
≤
25V (note 9)
2.85
0.9
3.00
1.0
70
-3.0
-10
3.15
1.1
V/V
V
dB
µA
V
OSC
f
T
J
= 25 C
12V
≤
V
CC
≤
25V
T
MIN
≤
T
A
≤
T
MAX
O
Symbol
Test Conditions
Min.
Typ.
Max.
Units
V
REF
T
J
= 25 C, I
REF
= 1mA
12V
≤
V
CC
≤
25V,T
J
= 25 C
O
O
4.9
5.0
6
6
5.1
20
25
-180
57
1.0
V
mV
mV
mA
KHz
%
%
V
1mA
≤
I
REF
≤
20mA
I
SC
T
J
= 25 C
O
-30
47
-100
52
0.2
5
1.7
2001/06/27
Advanced
Champion Microelectronic Corporation
Page 4
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