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PDF UC3845 Data sheet ( Hoja de datos )
| Número de pieza | UC3845 | |
| Descripción | (UC3842 - UC3845) CURRENTMODE PWM CONTROLLER | |
| Fabricantes | ST Microelectronics | |
| Logotipo |  |
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UC2842/3/4/5
® UC3842/3/4/5
CURRENT MODE PWM CONTROLLER
. OPTIMIZED FOR OFF-LINE AND DC TO DC
CONVERTERS
. LOW START-UP CURRENT (< 1 mA)
. AUTOMATIC FEED FORWARD COMPENSA-
TION
. PULSE-BY-PULSE CURRENT LIMITING
. ENHANCED LOAD RESPONSE CHARAC-
TERISTICS
. UNDER-VOLTAGE LOCKOUT WITH HYSTER-
ESIS
. DOUBLE PULSE SUPPRESSION
. HIGH CURRENT TOTEM POLE OUTPUT
. INTERNALLY TRIMMED BANDGAP REFER-
ENCE
. 500 KHz OPERATION
. LOW RO ERROR AMP
DESCRIPTION
TheUC3842/3/4/5family of controlICs provides the
necessary features to implement off-line or DC to
DC fixed frequency current mode control schemes
with a minimal externalparts count.Internallyimple-
mentedcircuits include undervoltagelockout featur-
ing start-up current less than 1 mA, a precision ref-
erence trimmed for accuracy at the error amp input,
Minidip
SO14
logic to insure latched operation, a PWM compara-
torwhich also providescurrentlimit control,and a to-
tem pole output stage designed to source or sink
high peak current. The output stage, suitable for
driving N-Channel MOSFETs, is low in theoff-state.
Differences between members of this family are the
under-voltage lockout thresholds and maximum
duty cycle ranges. The UC3842 and UC3844 have
UVLO thresholds of 16V (on) and 10V (off), ideally
suited off-line applications The corresponding
thresholds for the UC3843 and UC3845 are 8.5 V
and 7.9 V. The UC3842 and UC3843 can operate
to duty cycles approaching 100%. A range of the
zero to < 50 % is obtained by the UC3844 and
UC3845 by the additionof an internal toggle flip flop
which blanks the output off every other clock cycle.
BLOCK DIAGRAM (toggle flip flop used only in U3844 and UC3845)
October 1998
1/11
1 page  
Figure 1 : Error Amp Configuration.
Error amp can source or
sink up to 0.5mA
Figure 2 : Under Voltage Lockout.
UC2842/3/4/5-UC3842/3/4/5
During Under-Voltage Lockout, the output driver is
biased to sink minor amounts of current. Pin 6
should be shunted to groundwith a bleederresistor
Figure 3 : Current Sense Circuit .
to preventactivating the power switch with extrane-
ous leakage currents.
Peak current (is) is determined by the formula
IS
max
≈
1.0 V
RS
A small RC filter may be required to suppress switch transients.
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5 Page 
UC2842/3/4/5-UC3842/3/4/5
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the conse-
quences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No
license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this
publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMi-
croelectronics products are not authorized for use as critical components in life support devices or systems without express written
approval of STMicroelectronics.
The ST logo is a registered trademark of STMicroelectronics
© 1998 STMicroelectronics – Printed in Italy – All Rights Reserved
STMicroelectronics GROUP OF COMPANIES
Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Mexico - Morocco - The Netherlands -
Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A.
http://www.st.com
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11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet UC3845.PDF ] | |
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