Texas Instruments UC2845AQDR

Overview

UC2845AQDR from Texas Instruments is a current-mode PWM controller IC designed for off-line and DC-DC converters, featuring 8.5 V UVLO turn-on threshold, 7.9 V UVLO hysteresis, <50% maximum duty cycle, ±2000 V HBM ESD rating, and operation across –40°C to 125°C. It delivers high-current totem-pole output (±1 A), low start-up current (<0.5 mA), and trimmed oscillator discharge current (8.3 mA) for stable flyback and forward converter control in industrial power supplies.

For engineers reviewing the UC2845AQDR datasheet, UC2845AQDR pinout, UC2845AQDR application, or UC2845AQDR equivalent, this page provides verified package mapping (SOIC-14), confirmed pin functions, real-world SMPS implementation constraints, and validated alternative options for duty-cycle-limited current-mode control designs.

Technical Context

The UC2845AQDR implements fixed-frequency current-mode control with a toggle flip-flop enabling 50% max duty cycle limitation-distinct from UC2842/43 variants-making it suitable for forward converters requiring inherent duty-cycle clamping. Its error amplifier features 90 dB open-loop gain and 1 MHz unity-gain bandwidth, while the current sense comparator includes internal 1 V clamp and 70 dB PSRR.

Oscillator frequency is set via external RT/CT network (e.g., 10 kΩ + 3.3 nF yields ~52 kHz), with trimmed discharge current (7.5–8.8 mA) ensuring tight frequency tolerance. The device integrates an internally trimmed 5.0 V bandgap reference (±1% over temperature), low-ro error amp, and double-pulse suppression logic to prevent false triggering during transient recovery.

Key Specifications

Pinout & Package

UC2845AQDR is housed in a SOIC-14 package (8.65 mm × 6.00 mm, 1.75 mm max height), RoHS-compliant with NIPDAU lead finish and MSL Level-1 rating. Pin 1 is marked via notch or beveled corner; leads are gull-wing with 1.27 mm pitch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC2844AQDR, UC2845AQDR enables lower-VIN operation and tighter brownout immunity; versus TL494CDR, it provides inherent current-mode advantages-simpler loop compensation, better line rejection, and intrinsic overcurrent safety-without sacrificing SOIC-14 footprint compatibility.

Availability

UC2845AQDR is available at Aetrix Electronics and suitable for industrial DC-DC converters, isolated flyback power supplies, and forward converter designs requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for UC2845AQDR 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and power management technologies, with decades of expertise in power conversion ICs and industrial-grade reliability.

The UC284x family was engineered specifically for cost-sensitive, high-reliability current-mode SMPS control-targeting industrial, telecom, and battery-powered systems where thermal resilience, UVLO precision, and duty-cycle safety are critical.

FAQ

What is the maximum operating frequency of UC2845AQDR?

The UC2845AQDR supports up to 500 kHz operation per datasheet specification, though typical designs using standard RT/CT values (e.g., 10 kΩ + 3.3 nF) achieve ~52 kHz. Frequency scales inversely with RT and CT; minimum practical RT is 5 kΩ and maximum CT is 4.7 nF per TI recommendations. At 500 kHz, layout parasitics and gate drive losses require careful optimization-UC2845AQDR's 150 ns rise/fall times remain valid, but thermal derating becomes essential.

Does UC2845AQDR support synchronous rectification?

UC2845AQDR does not integrate synchronous rectifier drivers or dedicated SR control logic. Its single OUTPUT pin is designed for driving one external MOSFET in flyback, forward, or buck configurations. Synchronous rectification requires external circuitry-such as a dedicated SR controller (e.g., UCC24612) or discrete timing-based gate drive-to coordinate secondary-side FET switching. UC2845AQDR's 50% max duty cycle and current-mode sensing provide stable primary-side control, but SR timing must be derived externally.

How does the UVLO hysteresis of UC2845AQDR affect system startup behavior?

UC2845AQDR's UVLO turns on at 8.5 V and turns off at 7.9 V, providing 0.6 V hysteresis. This prevents oscillatory startup if VCC sags momentarily during capacitor charging or under heavy load. During cold start, the controller remains disabled until VCC crosses 8.5 V; once active, it continues operating down to 7.9 V before latching off. This behavior ensures clean, single-pulse initiation and avoids repeated enable/disable cycles that could stress magnetics or cause audible noise in transformers.

Can UC2845AQDR replace UC2845AD8 in an existing design?

No-UC2845AQDR (SOIC-14) is not pin-compatible with UC2845AD8 (SOIC-8). The SOIC-14 variant adds dedicated PWR GND, VS, and NC pins, separates analog and power grounds, and reassigns COMP/VFB/ISENSE functions. Layout, bypassing, and compensation networks differ significantly. Migration requires PCB redesign, ground partitioning updates, and verification of COMP loop stability. UC2845AQDR is intended for higher-power or noise-sensitive applications where SOIC-8 thermal and routing limitations apply.

What is the purpose of the VREF pin on UC2845AQDR, and what load can it drive?

The VREF pin on UC2845AQDR provides a stable 5.0 V ±1% output used to bias the optocoupler LED in isolated feedback paths and set RT/CT timing thresholds. It can source up to 20 mA continuously; exceeding this causes reference droop and oscillator frequency drift. For optocouplers like PC817, a 1 kΩ series resistor limits current to ~3 mA-well within spec. Bulk capacitance ≥10× the main FET's gate charge is mandatory to absorb switching transients and maintain regulation.