UC2845B

AC DC Converters, Offline Switchers Overview

The UC2845B is a high-performance current mode PWM controller manufactured by UMW, designed for off-line and DC-to-DC converter applications. It operates with a switching frequency up to 500 kHz and supports half-bridge topologies. The device features an internal oscillator trimmed for precise frequency control at 250 kHz, ensuring stable operation. It includes undervoltage lockout thresholds of 7.6 V (off) and 8.5 V (on), suitable for lower voltage applications. The IC provides cycle-by-cycle current limiting and adjustable output deadtime ranging from 50% to 70%. It is housed in an 8-SOIC package and functions within a supply voltage range of 7.6 V to 30 V.

AC DC Converters, Offline Switchers Feature Summary

• Current mode control architecture with integrated high-current totem pole output stage for driving power MOSFETs
• Internal toggle flip-flop mechanism that blanks the output every other oscillator cycle to enable half-bridge operation
• Programmable output deadtime adjustable between 50% and 70% via external resistor
• Integrated protective features including input undervoltage lockout with hysteresis and latching PWM for cycle-by-cycle current limiting

AC DC Converters, Offline Switchers Applications

• Half-bridge switched-mode power supplies
• Off-line AC-to-DC converters
• DC-to-DC isolated converter designs

AC DC Converters, Offline Switchers Procurement Notes

Verify the manufacturer marking on the component surface to confirm it originates from UMW rather than other producers such as ON Semiconductor or STMicroelectronics, as pinouts are generally compatible but electrical characteristics may vary slightly. Ensure the specific suffix indicates the correct package type, typically SOIC-8 for this model. Cross-reference the datasheet revision date to confirm compatibility with your design requirements regarding operating temperature and UVLO thresholds.

AC DC Converters, Offline Switchers Selection Notes

Select the UC2845B when designing half-bridge topologies requiring fixed-frequency current mode control. This component is appropriate for applications needing an internal toggle flip-flop to manage output deadtime automatically. It is suitable for systems operating within the 7.6 V to 30 V supply range where lower UVLO thresholds are preferred over the higher thresholds found in UC2844B variants. Consider thermal management requirements associated with the 8-SOIC package for continuous operation.

AC DC Converters, Offline Switchers Part Context

The UC2845B belongs to the UC284x family of current mode PWM controllers, which also includes the UC2842B, UC2843B, and UC2844B. These devices share a common functional block diagram but differ primarily in their undervoltage lockout thresholds and maximum duty cycle capabilities. The UC2845B is specifically distinguished by its lower UVLO thresholds and the inclusion of a toggle flip-flop for half-bridge applications, contrasting with the UC2844B which offers a different duty cycle range.

AC DC Converters, Offline Switchers Replacement Considerations

• UC2845BDG
• UC2845BDR2G

AC DC Converters, Offline Switchers FAQ

What is the primary difference between the UC2845B and UC2844B?

The UC2845B is designed for half-bridge applications with an internal toggle flip-flop that limits the duty cycle to less than 50% per cycle, whereas the UC2844B is intended for push-pull configurations and allows duty cycles approaching 100%.

How is the output deadtime controlled in the UC2845B?

The output deadtime is programmable and can be adjusted from 50% to 70% by connecting an external resistor between the RT/CT pin and ground.