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KA3842B/KA3843B/KA3844B/
KA3845B
SMPS Controller
Features
•
•
•
•
Low Start up Current
Maximum Duty Clamp
UVLO With Hysteresis
Operating Frequency up to 500KHz
Description
The KA3842B/KA3843B/KA3844B/KA3845B are fixed
frequency current-mode PWM controller. They are
specially designed for Off - Line and DC-to-DC converter
applications with minimum external components. These
integrated circuits feature a trimmed oscillator for precise
duty cycle control, a temperature compensated reference,
high gain error amplifier, current sensing comparator and a
high current totempole output for driving a power MOSFET.
The KA3842B and KA3844B have UVLO thresholds of
16V (on) and 10V (off). The KA3843B and KA3845B are
8.5V (on) and 7.9V (off). The KA3842B and KA3843B can
operate within 100% duty cycle. The KA3844B and
KA3845B can operate with 50% duty cycle.
8-DIP
1
14-SOP
1
Internal Block Diagram
Rev. 1.0.2
©2002 Fairchild Semiconductor Corporation
KA3842B/KA3843B/KA3844B/KA3845B
Absolute Maximum Ratings
Parameter
Supply Voltage
Output Current
Analog Inputs (Pin 2.3)
Error Amp Output Sink Current
Power Dissipation at T
A
≤25°C
(8DIP)
Power Dissipation at T
A
≤25°C
(14SOP)
Storage Temperature Range
Lead Temperature (Soldering, 10sec)
Symbol
V
CC
I
O
V
(ANA)
I
SINK (E.A)
P
D
(Note1,2)
P
D
(Note1,2)
T
STG
T
LEAD
Value
30
±1
-0.3 to 6.3
10
1200
680
-65 ~ +150
+300
Unit
V
A
V
mA
mW
mW
°C
°C
Note:
1. Board Thickness 1.6mm, Board Dimension 76.2mm
×114.3mm,
(Reference EIA / JSED51-3, 51-7)
2. Do not exceeed P
D
and SOA (Safe Operation Area)
Power Dissipation Curve
1200
8DIP
1100
POWER DISSIPATION (mW)
1000
900
800
700
600
500
400
300
0
10
20
30
40
50
60
70
80
90
100 110 120 130 140 150
14SOP
AMBIENT TEMPERATURE (℃)
Thermal Data
Characteristic
Thermal Resistance Junction-ambient
Symbol
R
thj-amb(MAX)
8-DIP
100
14-SOP
180
Unit
°C/W
Pin Array
8DIP,8SOP
8-DIP
8
V
REF
14SOP
COMP 1
COMP 1
14 V
REF
V
FB
2
7
V
CC
N/C
2
13
N/C
CURRENT SENSE
3
6
OUTPUT
V
FB
3
12
V
CC
R
T/
C
T
4
5
GND
N/C 4
11 PWR V
C
CURRENT SENSE
5
10
OUTPUT
N/C
6
9
GND
R
T/
C
T
7
8
PWR GND
2
KA3842B/KA3843B/KA3844B/KA3845B
Electrical Characteristics
(V
CC
=15V, R
T
=10KΩ, C
T
=3.3nF, T
A
= 0°C to +70°C, unless otherwise specified)
Parameter
REFERENCE SECTION
Reference Output Voltage
Line Regulation
Load Regulation
Short Circuit Output Current
OSCILLATOR SECTION
Oscillation Frequency
Frequency Change with Voltage
Oscillator Amplitude
ERROR AMPLIFIER SECTION
Input Bias Current
Input Voltage
Open Loop Voltage Gain
Power Supply Rejection Ratio
Output Sink Current
Output Source Current
High Output Voltage
Low Output Voltage
CURRENT SENSE SECTION
Gain
Maximum Input Signal
Power Supply Rejection Ratio
Input Bias Current
OUTPUT SECTION
Low Output Voltage
High Output Voltage
Rise Time
Fall Time
Start Threshold
Min. Operating Voltage
(After Turn On)
V
OL
I
SINK
= 20mA
I
SINK
= 200mA
V
OH
t
R
t
F
I
SOURCE
= 20mA
I
SOURCE
= 200mA
T
J
= 25°C, C
L
= 1nF (Note 3)
T
J
= 25°C, C
L
= 1nF (Note 3)
KA3842B/KA3844B
KA3843B/KA3845B
KA3842B/KA3844B
KA3843B/KA3845B
-
-
13
12
-
-
14.5
7.8
8.5
7.0
0.08
1.4
13.5
13.0
45
35
16.0
8.4
10.0
7.6
0.4
2.2
-
-
150
150
17.5
9.0
11.5
8.2
V
V
V
V
ns
ns
V
V
V
V
G
V
V
I(MAX)
PSRR
I
BIAS
(Note 1 & 2)
V
pin1
= 5V(Note 1)
12V≤ V
CC
≤25V
(Note1,3)
-
2.85
0.9
-
-
3
1
70
-3
3.15
1.1
-
-10
V/V
V
dB
µA
I
BIAS
V
I(E>A)
G
VO
PSRR
I
SINK
I
SOURCE
V
OH
V
OL
V
pin1
= 2.5V
2V≤ V
O
≤4V
(Note3)
12V≤ V
CC
≤25V
(Note3)
V
pin2
= 2.7V, V
pin1
= 1.1V
V
pin2
= 2.3V, V
pin1
= 5V
V
pin2
= 2.3V, R
L
= 15KΩ to GND
V
pin2
= 2.7V, R
L
= 15KΩ to Pin 8
-
-
2.42
65
60
2
-0.6
5
-
-0.1
2.50
90
70
7
-1.0
6
0.8
-2
2.58
-
-
-
-
-
1.1
µA
V
dB
dB
mA
mA
V
V
f
∆f/∆V
CC
V
OSC
T
J
= 25°C
12V≤V
CC
≤25V
-
47
-
-
52
0.05
1.6
57
1
-
KHz
%
V
P-P
V
REF
∆V
REF
∆V
REF
I
SC
T
J
= 25°C, I
REF
= 1mA
12V≤V
CC
≤25V
1mA≤I
REF
≤20mA
T
A
= 25°C
4.90
-
-
-
5.00
6
6
-100
5.10
20
25
-180
V
mV
mV
mA
Symbol
Conditions
Min.
Typ.
Max.
Unit
UNDER-VOLTAGE LOCKOUT SECTION
V
TH(ST)
V
OPR(MIN)
3
KA3842B/KA3843B/KA3844B/KA3845B
Electrical Characteristics
(Continued)
(V
CC
=15V, R
T
=10KΩ, C
T
=3.3nF, T
A
= 0°C to +70°C unless otherwise specified)
Parameter
PWM SECTION
Max. Duty Cycle
Min. Duty Cycle
TOTAL STANDBY CURRENT
Start-Up Current
Operating Supply Current
Zener Voltage
I
ST
I
CC(OPR)
V
Z
I
CC
= 25mA
-
V
pin3
=V
pin2
=ON
-
-
30
0.45
14
38
1
17
-
mA
mA
V
D
(Max)
D
(MAX)
D
(MIN)
KA3842B/KA3843B
KA3844B/KA3845B
-
95
47
-
97
48
-
100
50
0
%
%
%
Symbol
Conditions
Min.
Typ.
Max.
Unit
Adjust V
CC
above the start threshould before setting at 15V
Note:
1. Parameter measured at trip point of latch
2. Gain defined as:
∆V
pin1
A
= -----------------
,0
≤
V
pin3
≤
0.8V
-
∆V
pin3
3. These parameters, although guaranteed, are not 100 tested in production.
Figure 1. Open Loop Test Circuit
High peak currents associated with capacitive loads necessitate careful grounding techniques Timing and bypass capacitors
should be connected close to pin 5 in a single point ground. The transistor and 5KΩ potentiometer are used to sample the
oscillator waveform and apply an adjustable ramp to pin 3.
4
