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UC2842A Datasheet(PDF) 1 Page - STMicroelectronics

Part No. UC2842A
Description  HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
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Maker  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com
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UC2842A Datasheet(HTML) 1 Page - STMicroelectronics

 
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UC284XA
UC384XA
May 2004
1
FEATURES
TRIMMED OSCILLATOR DISCHARGE
CURRENT
CURRENT MODE OPERATION TO 500kHz
AUTOMATIC FEED FORWARD
COMPENSATION
LATCHING PWM FOR CYCLE-BY-CYCLE
CURRENT LIMITING
INTERNALLY TRIMMED REFERENCE WITH
UNDERVOLTAGE LOCKOUT
HIGH CURRENT TOTEM POLE OUTPUT
UNDERVOLTAGE LOCKOUT WITH
HYSTERESIS
LOW START-UP CURRENT (< 0.5mA)
DOUBLE PULSE SUPPRESSION
2
DESCRIPTION
The UC384xA family of control ICs provides the
necessary features to implement off-line or DC to
DC fixed frequency current mode control schemes
with a minimal external parts count. Internally im-
plemented circuits include a trimmed oscillator for
precise DUTY CYCLE CONTROL under voltage
lockout featuring start-up current less than 0.5mA,
a precision reference trimmed for accuracy at the
error amp input, logic to insure latched operation,
a PWM comparator which also provides current
limit control, and a totem pole output stage de-
signed to source or sink high peak current. The
output stage, suitable for driving N-Channel MOS-
FETs, is low in the off-state.
Differences between members of this family are
the under-voltage lockout thresholds and maxi-
mum duty cycle ranges. The UC3842A and
UC3844A have UVLO thresholds of 16V (on) and
10V (off), ideally suited off-line applications The
corresponding thresholds for the UC3843A and
UC3845A are 8.5 V and 7.9V. The UC3842A and
UC3843A can operate to duty cycles approaching
100%. A range of the zero to < 50 % is obtained by
the UC3844A and UC3845A by the addition of an
internal toggle flip flop which blanks the output off
every other clock cycle.
NOT FOR NEW DESIGN
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
Figure 2. Block Diagram (toggle flip flop used only in UC3844A and UC3845A)
UVLO
S/R
5V
REF
34V
INTERNAL
BIAS
VREF GOOD
LOGIC
2.50V
T
S
R
OSC
R1V
CURRENT
SENSE
COMPARATOR
2R
+
-
PWM
LATCH
7
5
4
2
1
3
8
6
ERROR AMP.
Vi
GROUND
RT/CT
VFB
COMP
CURRENT
SENSE
VREF
5V 50mA
OUTPUT
D95IN331
REV. 5
Figure 1. Package
Table 1. Order Codes
Part Number
Package
UC2842AD1; UC3842AD1;
UC2843AD1; UC3843AD1;
UC2844AD1; UC3844AD1;
UC2845AD1; UC3845AD1
SO-8
UC2842AN; UC3842AN;
UC2843AN; UC3843AN;
UC2844AN; UC3844AN;
UC2845AN; UC3845AN
DIP-8
SO-8
DIP-8


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