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UC3842ADX

P1-P3P4-P6P7-P8
©2000 Fairchild Semiconductor International
www.fairchildsemi.com
Rev. 5.0
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
8-SOP
1
1
Internal Block Diagram
8
+
-
7
5
SET/
RESET
5V
V
REF
Internal
Bias
Good LOGIC
2
R
S
OSCILLATOR
1
3
4
T
7
6
5
UVLO
29V
22V
1/3
Error Amp
1/2V
REF
1V
C.S
Comp.
PWM
LATCH
V
REF
V
FB
COMP
C.S
R
T/CT
OUTPUT
V
CC
GND
PWR
V
C
PWR
GND
UC3842A/UC3843A
SMPS Controller
UC3842A/UC3843A
2
Absolute Maximum Ratings
Electrical Characteristics
(V
CC
= 15V, R
T
= 10KΩ, C
T
= 3.3nF, T
A
= 0°C to + 70°C ,Unless otherwise specified)
Parameter Symbol Value Unit
Supply Voltage V
CC
30 V
Output Current I
O
± 1 A
Analog Inputs (pin 2, 3) V
I(ANA)
- 0.3 to 6.3 V
Error Amp. Output Sink Current I
SINK(EA)
10 mA
Power Dissipation P
D
1W
Parameter Symbol Conditions Min. Typ. Max. Unit
REFERENCE SECTION
Output Voltage V
REF
T
J
= 25°C, I
O
= 1mA 4.9 5.0 5.1 V
Line Regulation ∆V
REF
V
CC
= 12V to 25V - 6 20 mV
Load Regulation ∆V
REF
I
O
= 1mA to 20mA - 6 25 mV
Output Short Circuit I
SC
T
a
= 25°C - - 100 - 180 mA
OSILLATOR SECTION
Initial Accuracy F
OSC
T
J
= 25°C 47 52 57 KHz
Voltage Stability ST
V
V
CC
= 12V to 25V - 0.2 1 %
Amplitude V
OSC
V
PIN4
, Peak to Peak - 1.7 - V
Discharge Current I
DISCHG
T
J
= 25°C, Pin4 = 2V 7.8 8.3 8.8 mA
CURRENT SENSE SECTION
Gain G
V
(NOTE 2, 3) 2.85 3 3.15 V/V
Maximum Input Signal V
I(MAX)
V
PIN1
= 5V(NOTE 2) 0.9 1.0 1.1 V
PSRR PSRR V
CC
= 12V to 25V (NOTE 1, 2) - 70 - dB
Input Bias Current I
BIAS
- - - 2 -10 uA
Delay to Output T
D
V
PIN3
= 0 V to 2V (NOTE1) - 100 200 ns
UC3842A/UC3843A
3
Electrical Characteristics (Continued)
(V
CC
= 15V, R
T
= 10KΩ, C
T
= 3.3nF, T
A
= 0°C to + 70°C, Unless otherwise specified)
* 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)
Parameter Symbol Conditions Min. Typ. Max. Unit
ERROR AMPLIFIER SECTION
Input Voltage V
I
T
PIN1
= 2.5V 2.42 2.50 2.58 V
Input Bias Current I
BIAS
- - -0.3 - 2 uA
Open Loop Gain G
VO
V
O
= 2V to 4V (NOTE 1) 65 90 - dB
Unity Gain Bandwidth GBW T
J
= 25°C (NOTE 1) 0.7 1 - MHz
PSRR PSRR V
CC
= 12V to 25V (NOTE 1) 60 70 - dB
Output Sink Current I
SINK
V
PIN2
= 2.7V
V
PIN1
= 1.1V
26-mA
Output Source Current I
SOURCE
V
PIN2
= 2.3V
V
PIN1
= 5.0V
-0.5 -0.8 - mA
Output High Voltage V
OH
V
PIN2
= 2.3V
R1 = 15KΩ to GND
56-V
Output Low Voltage V
OL
V
PIN2
= 2.7V
R1 = 15KΩ to Pin8
-0.81.1V
OUTPUT SECTION
Output Low Level V
OL
I
SINK
= 20mA - 0.1 0.4 V
I
SINK
= 200mA - 1.5 2.2 V
Output High Level V
OH
I
SOURCE
= 20mA 13 13.5 - V
I
SOURCE
= 200mA 12 13.5 - V
Rise Time t
R
T
J
= 25°C, C1 = 1nF (NOTE 1) - 40 100 ns
Fall Time t
F
T
J
= 25°C, C1 = 1nF (NOTE 1) - 40 100 ns
Output Voltage Swing Limit V
OLIM
V
CC
= 27V, C1 = 1nF - 22 - V
UNDER VOLTAGE LOCKOUT SECTION
Start Threshold V
TH
UC3842A 15 16 17 V
UC3843A 7.8 8.4 9.0 V
Min. Operating Voltage
( After turn on )
V
TL
UC3842A 9 10 11 V
UC3843A 7.0 7.6 8.2 V
PWM SECTION
Maximum Duty Cycle D
MAX
UC3842A/UC3843A 94 96 100 %
Minimum Duty Cycle D
MIN
- --0%
TOTAL STANDBY CURRENT
Start-Up Current I
ST
- -0.20.4mA
Operating Supply Current I
CC
V
PIN2
= V
PIN3
= 0V - 11 17 mA
V
CC
Zener Voltage V
Z
I
CC
= 25mA - 29 - V
P1-P3P4-P6P7-P8

UC3842ADX

Mfr. #:
Buy UC3842ADX
Manufacturer:
ON Semiconductor
Description:
IC REG CTRLR PWM 8SOIC
Lifecycle:
New from this manufacturer.
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