STMicroelectronics E-UC2845BD1

Overview

E-UC2845BD1 from STMicroelectronics is a current-mode PWM controller IC designed for DC-DC and off-line power supplies, featuring 8.4 V UVLO turn-on threshold, 7.6 V UVLO hysteresis, ≤50% maximum duty cycle (due to internal toggle flip-flop), and guaranteed 250 kHz oscillator frequency with ±3% tolerance at 25°C. It delivers 1 A peak totem-pole output drive for N-channel MOSFETs and integrates a trimmed 5.00 V ±50 mV reference with <0.5 mA start-up current.

For engineers reviewing the E-UC2845BD1 datasheet, E-UC2845BD1 pinout, E-UC2845BD1 application, or E-UC2845BD1 equivalent, key selection criteria include UVLO thresholds for low-voltage input compatibility, 50% duty-cycle limitation for forward/flyback designs requiring reduced conduction time, current-sense gain of 3.0 V/V ±5%, and SO8 package thermal resistance of 150 °C/W.

Technical Context

The E-UC2845BD1 implements fixed-frequency current-mode control using an internally trimmed oscillator with RT/CT programmability (up to 500 kHz), a latched PWM comparator for cycle-by-cycle current limiting, and automatic feed-forward compensation via the error amplifier's high PSRR (70 dB). Its internal toggle flip-flop blanks the output every other clock cycle, enforcing ≤50% duty cycle - a defining architectural distinction from UC2842B/3B variants.

Control logic includes under-voltage lockout with hysteresis (8.4 V ON / 7.6 V OFF), a precision 2.5 V error amp reference input, and a 5 V reference output capable of sourcing up to 20 mA. The COMP pin provides direct access to the error amplifier output for loop compensation, while ISENSE accepts a voltage proportional to inductor current for real-time current limiting.

Key Specifications

Pinout & Package

Package: SO8 (Small Outline Integrated Circuit, 150 °C/W junction-to-ambient thermal resistance).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar current-mode PWM controller applications.

Compared with UC3845BN, E-UC2845BD1 offers superior thermal performance in SMT volume production, while NCP1200DR2G trades programmability and duty-cycle control for integration and cost - making E-UC2845BD1 optimal for designs requiring precise timing, low-voltage startup, and robust current limiting in compact form factors.

Availability

E-UC2845BD1 is available at Aetrix Electronics and suitable for AC-DC adapters, flyback SMPS, industrial DC-DC converters, and battery charger controllers requiring stable component supply, consistent parametric performance across temperature, and long-term industrial lifecycle support.

Supply support for E-UC2845BD1 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in power management, analog, microcontrollers, and automotive ICs.

The UC284xB series was developed specifically for cost-effective, high-reliability current-mode PWM control in off-line and DC-DC power supplies - emphasizing minimal external component count, precise oscillator trimming, and robust fault protection.

FAQ

What is the maximum recommended operating frequency for E-UC2845BD1?

The E-UC2845BD1 supports oscillator frequencies up to 500 kHz when configured with appropriate RT and CT values. However, its guaranteed specification is 250 kHz at 25°C. Operation above 300 kHz may reduce duty-cycle accuracy and increase propagation delay effects; thermal derating is required above 100 kHz in SO8 packages due to 150 °C/W thermal resistance.

Can E-UC2845BD1 drive a P-channel MOSFET directly?

No - E-UC2845BD1's OUTPUT pin is a totem-pole stage optimized for sinking current into the gate of N-channel MOSFETs. Driving a P-channel device would require level-shifting circuitry or an external inverter, as the IC lacks high-side drive capability or bootstrap support. Its low-state output ensures safe default-off behavior for N-MOSFETs.

How does the internal toggle flip-flop affect duty cycle in E-UC2845BD1?

The internal toggle flip-flop blanks the OUTPUT pin every other clock cycle, limiting maximum duty cycle to ≤50%. This is a hardwired feature distinguishing UC2844B/5B from UC2842B/3B. It prevents transformer saturation in forward converters and reduces RMS current stress in flyback designs - no external components are needed to enforce this constraint.

Is external slope compensation required when using E-UC2845BD1 in continuous conduction mode?

Yes - slope compensation is required for stable operation in continuous conduction mode (CCM) flyback or forward converters. The E-UC2845BD1 lacks built-in ramp injection; designers must add a sawtooth voltage (proportional to oscillator ramp) to the ISENSE node via external RC network or dedicated slope generator to prevent subharmonic oscillation at duty cycles >50%.