STMicroelectronics UC2843BD1

Overview

UC2843BD1 from STMicroelectronics is a high-performance current-mode PWM controller IC designed for fixed-frequency DC-DC and off-line power supplies. It features an internally trimmed 5V reference, under-voltage lockout with 8.5V turn-on/7.9V turn-off thresholds, latching PWM for cycle-by-cycle current limiting, oscillator frequency guaranteed at 250kHz (up to 500kHz), and a totem-pole output capable of ±1A peak drive current - enabling direct N-channel MOSFET gate driving in flyback, forward, and boost topologies.

For engineers reviewing the UC2843BD1 datasheet, UC2843BD1 pinout, UC2843BD1 application, or UC2843BD1 equivalent, key selection considerations include its low start-up current (<0.5mA), 94–100% maximum duty cycle capability, precise current-sense gain (3.0 V/V ±5%), internal oscillator discharge current (7.5–8.8 mA), and SO8 package compatibility with standard PCB layouts for cost-sensitive industrial and consumer power designs.

Technical Context

The UC2843BD1 implements current-mode control via a dedicated ISENSE input that compares a sensed inductor current ramp against the error amplifier output, triggering PWM latch reset on cycle-by-cycle overcurrent. Its oscillator uses RT/CT timing components with internal discharge current (7.5–8.8 mA) to set frequency and duty cycle, supporting operation up to 500kHz with minimal external parts.

Under-voltage lockout (UVLO) operates with asymmetric hysteresis (8.5V ON / 7.9V OFF), ensuring reliable startup and brownout recovery in low-input applications like 12V DC-DC converters. The error amplifier features 65–90 dB open-loop gain, 0.7–1 MHz unity-gain bandwidth, and rail-to-rail output swing into 15kΩ load - optimized for Type II/III compensation in current-mode topologies.

Key Specifications

Pinout & Package

UC2843BD1 is housed in an industry-standard SO8 (Small Outline 8-pin) package with 1.27 mm pitch, compliant with JEDEC MS-012, suitable for automated assembly and thermal management up to 800 mW at 25°C ambient.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC3843BD1, UC2843BD1 offers wider temperature qualification and identical performance - making it preferred for industrial deployments; versus NCP1200DR2G, UC2843BD1 trades higher start-up current for full duty-cycle flexibility and external timing control, essential for custom EMI shaping and multi-topology reuse.

Availability

UC2843BD1 is available at Aetrix Electronics and suitable for AC-DC adapters, flyback SMPS, DC-DC boost converters, and offline LED drivers requiring stable component supply, long-lifecycle support, and industrial-grade temperature performance.

Supply support for UC2843BD1 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, delivering silicon solutions for automotive, industrial, power, and embedded markets since 1987.

The UC284xB family was developed specifically for cost-sensitive, high-reliability current-mode switch-mode power supplies - targeting industrial, telecom, and consumer power applications where precision, latch protection, and SO8 manufacturability are critical.

FAQ

What is the minimum recommended RT resistor value for stable 250kHz operation?

The datasheet specifies RT = 10 kΩ with CT = 3.3 nF for nominal 250 kHz operation. Minimum RT is not explicitly defined, but practical lower limit is ~6.2 kΩ (per oscillator frequency table), yielding ~275 kHz. Using RT < 6.2 kΩ risks exceeding 500 kHz maximum rating and may degrade duty cycle accuracy due to oscillator discharge current nonlinearity above 8.8 mA.

Can UC2843BD1 operate without an external CT capacitor?

No - CT is mandatory for oscillator function. The internal oscillator relies on external RT and CT to set frequency and discharge timing. Omitting CT disables oscillation entirely, resulting in no PWM output. A minimum CT of 100 pF is recommended per Figure 2 to ensure stable startup and avoid subharmonic oscillation at low frequencies.

How does the UC2843BD1 handle overvoltage on the VREF pin?

VREF (pin 8) is specified for analog inputs of –0.3 V to 5.5 V. Exceeding 5.5 V risks damaging the internal bandgap reference. External circuits must limit VREF voltage - e.g., using series resistor + Zener clamp - especially when sourcing >20 mA or connecting to noisy supplies. The 5V output is not short-circuit protected beyond its 25 mA absolute max sink current rating.

Is slope compensation required when using UC2843BD1 in continuous conduction mode (CCM)?

Yes - slope compensation is required for stable CCM operation in boost, flyback, and forward converters. Without it, subharmonic oscillation occurs at duty cycles >50%. The datasheet recommends injecting a sawtooth ramp (proportional to oscillator voltage) into the ISENSE node via resistor divider, as shown in Figure 18. Slope magnitude should equal or exceed half the down-slope of the inductor current waveform.