Texas Instruments UC2845D8TRG4

Overview

UC2845D8TRG4 from Texas Instruments is a current-mode PWM controller IC designed for regulated DC-DC converter applications, featuring 8.4 V turn-on / 7.6 V turn-off UVLO thresholds, ≤1 mA start-up current, 50% maximum duty cycle, and up to 500 kHz oscillator frequency. It drives N-channel MOSFETs via a high-current totem-pole output stage and supports fixed-frequency operation with external RT/CT timing network.

For engineers reviewing the UC2845D8TRG4 datasheet, UC2845D8TRG4 pinout, UC2845D8TRG4 application, or UC2845D8TRG4 equivalent, key selection criteria include its narrow UVLO hysteresis (0.8 V), internal toggle flip-flop limiting duty cycle to ≤50%, compatibility with voltage-mode control via ISENSE ramp injection, and SOIC-8 package thermal performance (R_θJA = 117.4°C/W).

Technical Context

The UC2845D8TRG4 implements current-mode control using an internal PWM comparator that terminates switch conduction based on ISENSE voltage, with gain of 3 V/V and 150–300 ns delay. Its oscillator uses RT/CT pin with 1.72/(R_RT × C_CT) frequency equation and supports up to 500 kHz operation.

A built-in toggle flip-flop halves the OUTPUT switching frequency relative to f_OSC, enforcing ≤50% duty cycle and enabling stable operation in forward or push-pull topologies requiring symmetrical drive. The error amplifier features 65–90 dB open-loop gain, 0.7–1 MHz unity-gain bandwidth, and low-output-resistance design for direct compensation network connection at COMP pin.

Key Specifications

Pinout & Package

UC2845D8TRG4 is housed in an 8-pin SOIC (D) package measuring 4.90 mm × 6.00 mm, with standard JEDEC MS-012AC footprint and gull-wing leads. Thermal resistance is R_θJA = 117.4°C/W and R_θJC(top) = 51.5°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC2844D8TRG4 and UC3845N, UC2845D8TRG4 uniquely balances narrow UVLO hysteresis, industrial temperature rating (–40°C to 85°C), and SOIC-8 thermal/electrical performance for regulated DC-DC systems requiring reliable startup and sustained operation.

Availability

UC2845D8TRG4 is available at Aetrix Electronics and suitable for isolated forward converters, regulated buck converters, push-pull DC-DC converters, and digital power supply sequencers requiring stable component supply across industrial temperature ranges.

Supply support for UC2845D8TRG4 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 company specializing in analog and embedded processing technologies, with leadership in power management ICs and industrial-grade controllers.

The UC284x product line delivers cost-optimized, current-mode PWM controllers for regulated DC-DC applications, emphasizing low start-up current, precise UVLO thresholds, and robust gate drive capability in compact packages.

FAQ

What is the UVLO threshold behavior of UC2845D8TRG4?

The UC2845D8TRG4 features undervoltage lockout with a turn-on threshold of 8.4 V and turn-off threshold of 7.6 V, yielding 0.8 V hysteresis. This narrow window ensures reliable startup and shutdown in regulated DC-DC systems where input voltage remains stable above 8.4 V during normal operation. The UC2845D8TRG4 uses this hysteresis to reject noise and prevent oscillatory enable/disable cycling near the threshold.

How does UC2845D8TRG4 achieve 50% maximum duty cycle?

The UC2845D8TRG4 enforces ≤50% maximum duty cycle via an internal toggle flip-flop that blanks the OUTPUT pin every other oscillator cycle. This architecture is intrinsic to the UC2845D8TRG4 silicon design and cannot be disabled. It ensures safe operation in forward and push-pull topologies by preventing transformer core saturation, distinguishing UC2845D8TRG4 from UC2843D8TRG4 which supports up to 100% duty cycle.

Can UC2845D8TRG4 operate in voltage-mode control?

Yes, UC2845D8TRG4 supports voltage-mode control by injecting a sawtooth ramp signal onto the ISENSE pin, overriding its default current-sensing function. The UC2845D8TRG4's PWM comparator accepts this external ramp to establish fixed-frequency, variable-duty-cycle operation independent of primary current. This mode retains all protection features including pulse-by-pulse current limiting if the ramp amplitude is properly scaled.

What is the recommended bypassing for UC2845D8TRG4 VREF and VCC pins?

UC2845D8TRG4 requires a minimum 0.1 µF ceramic capacitor placed directly between VREF and GROUND, with short traces to minimize inductance. For VCC, a 0.1 µF ceramic capacitor must be placed adjacent to the pin, plus an additional bulk capacitor ≥10× the MOSFET gate capacitance to handle peak OUTPUT current transients. These requirements are specified in the UC2845D8TRG4 datasheet to ensure oscillator stability and reference accuracy.

Does UC2845D8TRG4 support synchronous rectification drive?

No, UC2845D8TRG4 does not natively support synchronous rectification drive. Its single OUTPUT pin is designed to drive only the primary-side N-channel MOSFET in flyback, forward, or buck configurations. Secondary-side synchronous rectifier control requires external circuitry - such as a dedicated SR controller or discrete logic - because UC2845D8TRG4 lacks auxiliary outputs, dead-time control, or adaptive timing for complementary gate drive.