datasheetbank_Logo
Integrated circuits, Transistor, Semiconductors Search and Datasheet PDF Download Site

UC2845A(1999) View Datasheet(PDF) - STMicroelectronics

Part Name
Description
View to exact match
UC2845A
(Rev.:1999)
ST-Microelectronics
STMicroelectronics ST-Microelectronics
UC2845A Datasheet PDF : 15 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
UC2842A/3A/4A/5A
®
UC3842A/3A/4A/5A
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
. TRIMMED OSCILLATOR DISCHARGE CUR-
RENT
. CURRENT MODE OPERATION TO 500kHz
. AUTOMATIC FEED FORWARD COMPENSA-
TION
. LATCHING PWM FOR CYCLE-BY-CYCLE
CURRENT LIMITING
. INTERNALLY TRIMMED REFERENCE WITH
UNDERVOLTAGE LOCKOUT
. HIGH CURRENT TOTEM POLE OUTPUT
. UNDERVOLTAGE LOCKOUT WITH HYSTER-
ESIS
. LOW START-UP CURRENT (< 0.5mA)
. DOUBLE PULSE SUPPRESSION
DESCRIPTION
TheUC384xA family ofcontrolICs providesthe nec-
essary features to implement off-line or DC to DC
fixed frequency current mode control schemes with
a minimal external parts count. Internally imple-
mented circuits include a trimmed oscillator for pre-
cise DUTY CYCLE CONTROL under voltage lock-
outfeaturingstart-up current less than0.5mA,a pre-
cision reference trimmed for accuracy at the error
amp input, logicto insure latched operation,a PWM
Minidip
SO8
comparatorwhich alsoprovidescurrent limit control,
and a totem pole output stage designed to source
or sink high peakcurrent. The outputstage, suitable
for driving N-Channel MOSFETs, is low in the off-
state.
Differences between members of this family are the
under-voltagelockout thresholds and maximum duty
cycle ranges. The UC3842A and UC3844A have
UVLO thresholds of 16V (on) and 10V (off), ideally
suited off-line applications The corresponding thresh-
olds for the UC3843A and UC3845A are 8.5 V and
7.9V. The UC3842A and UC3843A can operate to
dutycycles approaching100%.A range of the zeroto
< 50 % is obtainedby theUC3844Aand UC3845Aby
the addition of an internal toggle flip flopwhich blanks
the output off every otherclock cycle.
BLOCK DIAGRAM (toggle flip flop used only in UC3844A and UC3845A)
7
Vi
5
GROUND
4
RT/CT
2
VFB
1
COMP
CURRENT 3
SENSE
34V
UVLO
S/R
5V
REF
2.50V
OSC
VREF GOOD
LOGIC
INTERNAL
BIAS
T
8 VREF
5V 50mA
6
OUTPUT
ERROR AMP.
+
2R
-
R
S
R
1V
CURRENT
SENSE
COMPARATOR
PWM
LATCH
UC3842A
D95IN331
March 1999
1/15
 

Share Link: 

datasheetbank.com [ Privacy Policy ] [ Request Datasheet ] [ Contact Us ]