www.fairchildsemi.com
UC3842A/UC3843A
SMPS Controller
Features
•
•
•
•
•
•
•
Low Start Current 0.2mA (typ)
Operating Range Up To 500KHz
Cycle by Cycle Current Limiting
Under Voltage Lock Out With Hysteresis
Short Shutdown Delay Time: typ.100ns
High Current Totem-pole Output
Output Swing Limiting: 22V
Description
The UC3842A/UC3843A are fixed PWM controller for Off-
Line and DC to DC converter applications. The internal cir-
cuits include UVLO, low start up current circuit, tempera-
ture compensated reference, high gain error amplifier,
current sensing comparator, and high current totem-pole out-
put for driving a POWER MOSFET. Also UC3842A/
UC3843A provide low start up current below 0.3mA and
short shutdown delay time typ. 100ns. The UC3842A has
UVLO threshold of 16V(on) and 10V(off). The UC3843A is
8.4V(on) and 7.6V(off). The UC3842A and UC3843A can
operate within 100% duty cycle.
8-DIP
1
8-SOP
1
Internal Block Diagram
7
V
CC
29V
V
REF
8
Internal
Bias
1/2V
REF
5V
V
REF
SET/
RESET
UVLO
5
GND
Good LOGIC
7
PWR
V
C
V
FB
2
Error Amp
+
-
C.S
PWM
Comp. LATCH
1/3
1V
S
R
22V
6
OUTPUT
COMP
1
5
PWR
C.S
3
R
T
/C
T
4
T
GND
OSCILLATOR
Rev. 5.0
©2000 Fairchild Semiconductor International
UC3842A/UC3843A
Absolute Maximum Ratings
Parameter
Supply Voltage
Output Current
Analog Inputs (pin 2, 3)
Error Amp. Output Sink Current
Power Dissipation
Symbol
V
CC
I
O
V
I(ANA)
I
SINK(EA)
P
D
Value
30
±1
- 0.3 to 6.3
10
1
Unit
V
A
V
mA
W
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
Output Voltage
Line Regulation
Load Regulation
Output Short Circuit
OSILLATOR SECTION
Initial Accuracy
Voltage Stability
Amplitude
Discharge Current
CURRENT SENSE SECTION
Gain
Maximum Input Signal
PSRR
Input Bias Current
Delay to Output
G
V
V
I(MAX)
PSRR
I
BIAS
T
D
(NOTE 2, 3)
V
PIN1
= 5V(NOTE 2)
V
CC
= 12V to 25V (NOTE 1, 2)
-
V
PIN3
= 0 V to 2V (NOTE1)
2.85
0.9
-
-
-
3
1.0
70
-2
100
3.15
1.1
-
-10
200
V/V
V
dB
uA
ns
F
OSC
ST
V
V
OSC
I
DISCHG
T
J
= 25°C
V
CC
= 12V to 25V
V
PIN4
, Peak to Peak
T
J
= 25°C, Pin4 = 2V
47
-
-
7.8
52
0.2
1.7
8.3
57
1
-
8.8
KHz
%
V
mA
V
REF
∆V
REF
∆V
REF
I
SC
T
J
= 25°C, I
O
= 1mA
V
CC
= 12V to 25V
I
O
= 1mA to 20mA
T
a
= 25°C
4.9
-
-
-
5.0
6
5.1
20
V
mV
mV
mA
Symbol
Conditions
Min.
Typ.
Max.
Unit
6
25
- 100 - 180
2
UC3842A/UC3843A
Electrical Characteristics (Continued)
(V
CC
= 15V, R
T
= 10KΩ, C
T
= 3.3nF, T
A
= 0°C to + 70°C, Unless otherwise specified)
Parameter
ERROR AMPLIFIER SECTION
Input Voltage
Input Bias Current
Open Loop Gain
Unity Gain Bandwidth
PSRR
Output Sink Current
Output Source Current
Output High Voltage
Output Low Voltage
OUTPUT SECTION
Output Low Level
Output High Level
Rise Time
Fall Time
Output Voltage Swing Limit
V
OL
V
OH
t
R
t
F
V
OLIM
I
SINK
= 20mA
I
SINK
= 200mA
I
SOURCE
= 20mA
I
SOURCE
= 200mA
T
J
= 25°C, C1 = 1nF (NOTE 1)
T
J
= 25°C, C1 = 1nF (NOTE 1)
V
CC
= 27V, C1 = 1nF
UC3842A
UC3843A
UC3842A
UC3843A
UC3842A/UC3843A
-
-
V
PIN2
= V
PIN3
= 0V
I
CC
= 25mA
-
-
13
12
-
-
-
15
7.8
9
7.0
94
-
-
-
-
0.1
1.5
13.5
13.5
40
40
22
16
8.4
10
7.6
96
-
0.2
11
29
0.4
2.2
-
-
100
100
-
17
9.0
11
8.2
100
0
0.4
17
-
V
V
V
V
ns
ns
V
V
V
V
V
%
%
mA
mA
V
V
I
I
BIAS
G
VO
GBW
PSRR
I
SINK
I
SOURCE
V
OH
V
OL
T
PIN1
= 2.5V
-
V
O
= 2V to 4V (NOTE 1)
T
J
= 25°C (NOTE 1)
V
CC
= 12V to 25V (NOTE 1)
V
PIN2
= 2.7V
V
PIN1
= 1.1V
V
PIN2
= 2.3V
V
PIN1
= 5.0V
V
PIN2
= 2.3V
R1 = 15KΩ to GND
V
PIN2
= 2.7V
R1 = 15KΩ to Pin8
2.42
-
65
0.7
60
2
-0.5
5
-
2.50
-0.3
90
1
70
6
-0.8
6
0.8
2.58
-2
-
-
-
-
-
-
1.1
V
uA
dB
MHz
dB
mA
mA
V
V
Symbol
Conditions
Min.
Typ.
Max.
Unit
UNDER VOLTAGE LOCKOUT SECTION
Start Threshold
Min. Operating Voltage
( After turn on )
PWM SECTION
Maximum Duty Cycle
Minimum Duty Cycle
TOTAL STANDBY CURRENT
Start-Up Current
Operating Supply Current
V
CC
Zener Voltage
I
ST
I
CC
V
Z
D
MAX
D
MIN
V
TH
V
TL
* Adjust V
CC
above the start threshold before setting at 15V
Notes :
1. These parameters, although guaranteed, are not 100% tested in production.
2. Parameter measured at trip point of latch with V2 = 0V.
3. Gain defined as: G
V
=
∆V
PIN1
∆V
PIN3
(V
PIN3
= 0 to 0.8V)
3
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