UC1845

ACTIVE

Current Mode PWM Controller

Product details

Vin (max) (V) 30 Operating temperature range (°C) -55 to 125 Control mode Current Topology Boost, Flyback, Forward Rating Military Features Error amplifier, Multi-topology Duty cycle (max) (%) 50
Vin (max) (V) 30 Operating temperature range (°C) -55 to 125 Control mode Current Topology Boost, Flyback, Forward Rating Military Features Error amplifier, Multi-topology Duty cycle (max) (%) 50
CDIP (JG) 8 64.032 mm² 9.6 x 6.67 CFP (W) 14 58.023 mm² 9.21 x 6.3 LCCC (FK) 20 79.0321 mm² 8.89 x 8.89
  • Optimized for off-line and DC-to-DC converters
  • Low start-up current (< 1 mA)
  • Automatic feedforward compensation
  • Pulse-by-pulse current limiting
  • Enhanced load-response characteristics
  • Undervoltage lockout with hysteresis
  • Double-pulse suppression
  • High-current totem-pole output
  • Internally trimmed bandgap reference
  • Up to 500-kHz operation
  • Error amplifier with low output resistance
  • Optimized for off-line and DC-to-DC converters
  • Low start-up current (< 1 mA)
  • Automatic feedforward compensation
  • Pulse-by-pulse current limiting
  • Enhanced load-response characteristics
  • Undervoltage lockout with hysteresis
  • Double-pulse suppression
  • High-current totem-pole output
  • Internally trimmed bandgap reference
  • Up to 500-kHz operation
  • Error amplifier with low output resistance

The UCx84x series of control integrated circuits provide the features that are necessary to implement off-line or DC-to-DC fixed-frequency current-mode control schemes, with a minimum number of external components. The internally implemented circuits include an undervoltage lockout (UVLO), featuring a start-up current of less than 1 mA, and a precision reference trimmed for accuracy at the error amplifier input. Other internal circuits include logic to ensure latched operation, a pulse-width modulation (PWM) comparator that also provides current-limit control, and a totem-pole output stage that is designed to source or sink high-peak current. The output stage, suitable for driving N-channel MOSFETs, is low when it is in the off state.

The UCx84x family offers a variety of package options, temperature range options, choice of maximum duty cycle, and choice of turnon and turnoff thresholds and hysteresis ranges. Devices with higher turnon or turnoff hysteresis are ideal choices for off-line power supplies, while the devices with a narrower hysteresis range are suited for DC-DC applications. The UC184x devices are specified for operation from –55°C to 125°C, the UC284x series is specified for operation from –40°C to 85°C, and the UC384x series is specified for operation from 0°C to 70°C.

The UCx84x series of control integrated circuits provide the features that are necessary to implement off-line or DC-to-DC fixed-frequency current-mode control schemes, with a minimum number of external components. The internally implemented circuits include an undervoltage lockout (UVLO), featuring a start-up current of less than 1 mA, and a precision reference trimmed for accuracy at the error amplifier input. Other internal circuits include logic to ensure latched operation, a pulse-width modulation (PWM) comparator that also provides current-limit control, and a totem-pole output stage that is designed to source or sink high-peak current. The output stage, suitable for driving N-channel MOSFETs, is low when it is in the off state.

The UCx84x family offers a variety of package options, temperature range options, choice of maximum duty cycle, and choice of turnon and turnoff thresholds and hysteresis ranges. Devices with higher turnon or turnoff hysteresis are ideal choices for off-line power supplies, while the devices with a narrower hysteresis range are suited for DC-DC applications. The UC184x devices are specified for operation from –55°C to 125°C, the UC284x series is specified for operation from –40°C to 85°C, and the UC384x series is specified for operation from 0°C to 70°C.

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Technical documentation

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Type Title Date
* Data sheet UCx84x Current-Mode PWM Controllers datasheet (Rev. G) PDF | HTML 11 Jul 2022
* SMD UC1845 SMD 5962-86704 21 Jun 2016
White paper Understanding Functional Safety FIT Base Failure Rate Estimates per IEC 62380 and SN 29500 (Rev. A) PDF | HTML 30 Apr 2024
Application note Conditioning a Switch-mode Power Supply Current Signal Using TI Op Amps (Rev. A) PDF | HTML 11 Jun 2021
Application note Understanding Inverting Buck-Boost Power Stages in Switch Mode Power Supplies (Rev. B) 12 Mar 2019
Application note UCC38C42 Family of High-Speed BiCMOS Current-Mode PWM Controllers 07 Feb 2002
Application note DN-26 UC3842A Low-Cost Start-up and Fault Protection Circuit 05 Sep 1999
Application note DN-27 UC1842/UC1842A Family - Summary of Functional Differences 05 Sep 1999
Application note DN-29 UC3842A Family - Frequency Foldback Technique Provides Protection 05 Sep 1999
Application note DN-30 Programmable Electronic Circuit Breaker 05 Sep 1999
Application note DN-40 The Effects of Oscillator Discharge Current Variations on Maximum Duty 05 Sep 1999
Application note DN-42A Design Considerations for Transitioning from UC3842 to the New UCC3802 05 Sep 1999
Application note DN-62 Switching Power Supply Topology Voltage Mode vs. Current Mode 05 Sep 1999
Application note DN-65 Considerations in Powering BiCMOS ICs 05 Sep 1999
Application note DN-89 Comparing the UC3842, UCC3802, and UCC3809 Primary Side PWM Controllers 05 Sep 1999
Application note Modeling, Analysis and Compensation of the Current-Mode Converter 05 Sep 1999
Application note U-100A UC3842/3/4/5 Provides Low-Cost Current-Mode Control 05 Sep 1999
Application note U-111, Practical Considerations in Current Mode Power Supplies 05 Sep 1999

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