UC1842A/3A/4A/5A
UC2842A/3A/4A/5A
UC3842A/3A/4A/5A
Current Mode PWM Controller
FEATURES
DESCRIPTION
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Optimized for Off-line and DC to DC
The UC1842A/3A/4A/5A family of control ICs is a pin for pin compat-
ible improved version of the UC3842/3/4/5 family. Providing the nec-
essary features to control current mode switched mode power
supplies, this family has the following improved features. Start up cur-
rent is guaranteed to be less than 0.5mA. Oscillator discharge is
trimmed to 8.3mA. During under voltage lockout, the output stage can
sink at least 10mA at less than 1.2V for VCC over 5V.
Converters
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Low Start Up Current (<0.5mA)
Trimmed Oscillator Discharge Current
Automatic Feed Forward Compensation
Pulse-by-Pulse Current Limiting
Enhanced Load Response Characteristics
Under-Voltage Lockout With Hysteresis
Double Pulse Suppression
The difference between members of this family are shown in the table
below.
Maximum Duty
Part #
UVLO On
UVLO Off
Cycle
<100%
<100%
<50%
High Current Totem Pole Output
Internally Trimmed Bandgap Reference
500kHz Operation
UC1842A
UC1843A
UC1844A
UC1845A
16.0V
8.5V
10.0V
7.9V
16.0V
8.5V
10.0V
7.9V
<50%
Low RO Error Amp
BLOCK DIAGRAM
A/B
Note 1:
A = DIL-8 Pin Number. B = SO-14 Pin Number.
Note 2: Toggle flip flop used only in 1844A and 1845A.
9/94
TI [ TEXAS INSTRUMENTS ]
