UC3845
SMPS Controller

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      The UC1842/3/4/5 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 implemented circuits include under-voltage lockout featuring start up current less than1mA,aprecision reference trimmed for ac curacyat the error ampinput,logic to insure latched operation,a PWM comparator which also provide scurrentl imit control,and a totem poleout put stage designed to source or sink high peak current.The out put stage,suit able for driving N Channel MOSFETs,is low in the off state.

      Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges.The UC1842 and UC1844 have UVLO thresholds of 16V (on) and 10V (off),ideally suited to off-line applications.The corresponding thresholds for the UC1843 and UC1845 are 8.4V and 7.6V.The UC1842 and UC1843 can operate to duty cycles approaching 100%.A range of zero to 50% is obtained by the UC1844 and UC 1845 by the addition of an internal toggle flip flop which blanks the output off every other clock cycle.

Audio
Automotive
Broadband
Digital Control
Military
Optical Networking
Security
Telephony
Video & Imaging
Wireless
Supply Voltage(LowImpedanceSource)..................30V
Supply Voltage(ICC <30mA)...................... SelfLimiting
Output Current.................................................... ±1A
Output Energy(CapacitiveLoad) ............................5μJ
Analog Inputs(Pins2,3).......................... -0.3Vto+6.3V
Error Amp Output Sink Current ..........................10mA
Power Dissipation at TA≤25℃(DIL-8)................... 1W
Power Dissipation at TA≤25℃(SOIC-14).........725mW
StorageTemperatureRange.................-65℃ to+150℃
JunctionTemperatureRange ................-55℃ to+150℃
LeadTemperature(soldering,10seconds)........... 300℃
*Optimized For Off-line And DC To DC Converters
*Low Start Up Current (<1mA)
*Automatic Feed Forward Compensation
*Pulse-by-pulse Current Limiting
*Enhanced Load Response Characteristics
*Under-voltage Lockout With Hysteresis
*Double Pulse Suppression
*High Current Totem Pole Output
*Internally Trimmed Bandgap Reference
*500khz Operation
*Low RO Error Amp

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Datasheet

Size: 127.58KB
Page: 12
PDF: UC3845.pdf
  • Description:
    SMPS Controller
  • MFG:
    FAIRCHILD [Fairchild Semiconductor]
 

Abstract


?2002 Fairchild Semiconductor Corporation
www.fairchildsemi.com
Rev. 1.0.1
Features
? Low Start up Current
? Maximum Duty Clamp
? UVLO With Hysteresis
? Operating Frequency up to 500KHz
Description
The UC3842/UC3843/UC3844/UC3845 are fixed
frequencycurrent-mode PWM controller. They are specially
designed for Off-Line and DC to DC converter applications
with minimum external components. These integrated
circuits feature a trimmed oscillator for precise duty cycle
control, a temperature compensated reference, high gain
error amplifier, current sensing comparator and a high
current totempole output for driving a Power MOSFET. The
UC3842 and UC3844 have UVLO thresholds of 16V (on)
and 10V (off). The UC3843 and UC3845 are 8.5V(on) and
7.9V (off). The UC3842 and UC3843 can operate within
100% duty cycle. The UC3844 and UC3845 can operate
with 50% duty cycle.
8-DIP
14-SOP
1
1
8-SOP
1
Internal Block Diagram
UC3842/UC3843/UC3844/UC3845
SMPS Controller
* NORMALLY 8DIP/8SOP PIN NO.
* ( ) IS 14SOP PINNO.
* TOGGLE FLIP FLOP USED ONLY IN UC3844, UC3845

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