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UC3843
Fixed Frequency Current Mode PWM Controller
DESCRIPTION
UC3843 is a fixed frequency current-mode PWM controller.
It is specially designed for Off Line and DC-to-DC converter
applications with minimal external component. This
integrated circuit features a trimmed oscillator for precise
duty cycle control, a temperature compensated reference, a
high gain error amplifier, a current sensing comparator, and
a high current totem pole output ideally suited for driving a
power MOSFET.
The device is protective features consisting of input and
reference under-voltage lockouts each with hysteresis,
cycle-by-cycle current limiting.
PIN CONFIGURATION
Compensation
Voltage Feedback
Current Sense
RT/CT
1
2
3
4
8 Vref
7 VCC
6 Output
5 GND
(Top View)
FEATURES
● Automatic Feed Forward Compensation
● High Current Totem Pole Output
● Internally Trimmed Bandgap Reference
● Undervoltage Lockout with Hysteresis
● Low Start Up Current
● Optimized for offline converter
● Double pulse suppression
● Current mode operation to 500kHz
APPLICATION
● Wireless Base Station Power
● Telecom and Datacom Power
● Industrial Power Systems
● PC Power Supplies
ORDERING INFORMATION
Temperature Range
0°C to +70°C
Package
DIP8L
SOP8L
Pb-Free
Orderable
Device
UC3843D
UC3843P
Package Qty
75Units/Tube
50Units/Tube
Jun. 2008
Rev 1.0
1
UC3843
ELECTRICAL CHARACTERISTICS(CONTINUE)
Parameter
Symbol
Test Conditions
Min
Current Sense Section
Current Sense Input
Voltage Gain
AV
VFB = 0V, VCC = 15V,
TA = TLOW to THIGH
2.85
Maximum Current
Sense Input
Threshold
VTH
VFB = 0V,VCC = 15V,
TA = TLOW to THIGH
0.9
Input Bias Current
IIB
VCC = 15V,
TA = TLOW to THIGH
Propagation Delay
(Current Sense Input
to Output)
tPLH
VCC = 15V,
TA = TLOW to THIGH
Max
3.15
1.1
-10
300
Unit
V
μA
ns
Output Section
Output
Voltage
Low
State
High
State
Output Voltage with
UVLO Activated
VOL ISINK = 20mA, VCC = 15V
ISINK = 200mA, VCC = 15V
VOH ISINK = 20mA, VCC = 15V
ISINK = 200mA, VCC = 15V
VOL(UVLO)
VCC = 6V, ISINK = 1.0mA,
TA = TLOW to THIGH
13
12
0.4
2.2
1.1
Output Voltage
Rise Time
tr
CL = 1.0nF,VCC= 15V,
TA = TLOW to THIGH
150
Output Voltage Fall
Time
tf
CL = 1.0nF, VCC = 15V,
TA = TLOW to THIGH
150
Under Voltage Lockout Section
Startup Threshold
Minimum Operating
Voltage After Turn-On
Vth
VCC(MIN)
VCC = 0V to 25V,
TA = TLOW to THIGH
VCC = 0V to 25V,
TA = TLOW to THIGH
7.8 7.9
7.0 8.2
V
V
ns
ns
V
V
PWM Section
Duty Cycle
DC
Total Device
Power Supply Current ICC
VCC = 15V,
TA = TLOW to THIGH,
RT = 10KΩ, CT = 3.3nF
Startup: VCC = 14V
Operating: VCC = 15V
0 94
%
1.0
mA
17
Power Supply Zener
Voltage
Vz ICC = 25mA, VCC = 0 to 40V 30
40
V
Note 1: VFINAL = VREF25(RegLINE+RegLOAD)/1000±IVREF70(VREF0)-VREF25I VREF25 = VREF@TA=25°C;
VREF70=VREF@TA=70°C;VREF0=VREF@TA=0°C.
Note 2: TLOW = 0°C,THIGH=+70°C
Jun. 2008
Rev 1.0
5