UC3845B: High Performance Current Mode PWM Controller

The UC3844B, UC3845B series are high performance fixed frequency current mode controllers. They are specifically designed for Off-Line and dc-to-dc converter applications offering the designer a cost-effective solution with minimal external components. These integrated circuits feature an oscillator, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output ideally suited for driving a power MOSFET. Also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycle-by-cycle current limiting, a latch for single pulse metering, and a flip-flop which blanks the output off every other oscillator cycle, allowing output deadtimes to be programmed from 50% to 70%. These devices are available in an 8-pin dual-in-line and surface mount (SO-8) plastic package as well as the 14-pin plastic surface mount (SO-14). The SO-14 package has separate power and ground pins for the totem pole output stage. The UCX844B has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off-line converters. The UCX845B is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).

Features
  • Trimmed Oscillator for Precise Frequency Control
  • Oscillator Frequency Guaranteed at 250 kHz
  • Current Mode Operation to 500 kHz Output Switching Frequency
  • Output Deadtime Adjustable from 50% to 70%
  • 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 Startup and Operating Current
  • Pb-Free Packages are Available
Application Notes (2)
Document TitleDocument ID/SizeRevisionRevision Date
The One-Transistor Forward ConverterAND8039/D (172.0kB)1
Very Wide Input Voltage Range, Off-line Flyback Switching Power SupplyAN1327/D (326.0kB)2
Package Drawings (3)
Document TitleDocument ID/SizeRevision
8 LEAD PDIP626-05 (35.0kB)P
SOIC-14 NB751A-03 (34.3kB)L
SOIC-8 Narrow Body751-07 (62.6kB)AK
Data Sheets (1)
Document TitleDocument ID/SizeRevisionRevision Date
High Performance Current Mode ControllerUC3844B/D (393.0kB)11
Order Information
ProductStatusCompliancePackageMSL*ContainerBudgetary Price/Unit
UC3845BD1GActivePb-free Halide freeSOIC-8751-071Tube98$0.432
UC3845BD1R2GActivePb-free Halide freeSOIC-8751-071Tape and Reel2500$0.432
UC3845BDGActivePb-free Halide freeSOIC-14751A-031Tube55$0.2
UC3845BDR2GActivePb-free Halide freeSOIC-14751A-031Tape and Reel2500$0.48
UC3845BNGActivePb-free Halide freePDIP-8626-05NATube50$0.432
UC3845BVD1GActivePb-free Halide freeSOIC-8751-071Tube98$0.2667
UC3845BVD1R2GActivePb-free Halide freeSOIC-8751-071Tape and Reel2500$0.5733
UC3845BVDGActivePb-free Halide freeSOIC-14751A-031Tube55$0.2667
UC3845BVDR2GActivePb-free Halide freeSOIC-14751A-031Tape and Reel2500$0.2667
UC3845BVNGActivePb-free Halide freePDIP-8626-05NATube50$0.2667
Specifications
ProductTopologyControl Modefsw Typ (kHz)Stand-by ModeUVLO (V)Short Circuit ProtectionLatchSoft StartVCC Max (V)Drive Cap. (mA)
UC3845BD1GStep-Up Step-Down Forward FlybackCurrent Mode52NoYesYesNoNo25200 / 200
UC3845BD1R2GForward Flyback Step-Down Step-UpCurrent Mode52NoYesYesNoNo25200 / 200
UC3845BDGForward Step-Up Flyback Step-DownCurrent Mode52NoYesYesNoNo25200 / 200
UC3845BDR2GStep-Down Flyback Step-Up ForwardCurrent Mode52NoYesYesNoNo25200 / 200
UC3845BNGStep-Down Flyback Forward Step-UpCurrent Mode52NoYesYesNoNo25200 / 200
UC3845BVD1GStep-Down Flyback Forward Step-UpCurrent Mode52NoYesYesNoYes25200 / 200
UC3845BVD1R2GStep-Up Flyback Step-Down ForwardCurrent Mode52NoYesYesNoYes25200 / 200
UC3845BVDGStep-Up Flyback Step-Down ForwardCurrent Mode52NoYesYesNoYes25200 / 200
UC3845BVDR2GStep-Up Forward Step-Down FlybackCurrent Mode52NoYesYesNoYes25200 / 200
UC3845BVNGStep-Down Forward Step-Up FlybackCurrent Mode52NoYesYesNoYes25200 / 200
High Performance Current Mode Controller (393.0kB) UC3845B
The One-Transistor Forward Converter NDD05N50Z
Very Wide Input Voltage Range, Off-line Flyback Switching Power Supply MUR1100E
SOIC-8 Narrow Body CM1216
SOIC-14 NB NLSX5014
8 LEAD PDIP NE592