Texas Instruments UC3845DTR

Overview

UC3845DTR from Texas Instruments is a fixed-frequency current-mode PWM controller IC designed for DC-DC converter applications requiring regulated input voltage operation. It features 8.4 V turn-on / 7.6 V turn-off UVLO thresholds, 47–50% maximum duty cycle, 5 V ±2% internal reference, and up to 500 kHz oscillator frequency. The device drives N-channel MOSFETs via a 1 A peak totem-pole output stage and supports pulse-by-pulse current limiting in isolated or non-isolated buck, boost, and flyback topologies.

For engineers reviewing the UC3845DTR datasheet, UC3845DTR pinout, UC3845DTR application, or UC3845DTR equivalent, key selection criteria include its narrow UVLO hysteresis (0.8 V), 50% max duty cycle enforced by internal toggle flip-flop, SOIC-8 package footprint, and compatibility with DC-DC designs operating from 12–28 V input rails under 0°C to 70°C ambient conditions.

Technical Context

The UC3845DTR implements a current-mode control architecture with an integrated PWM comparator, error amplifier, undervoltage lockout with 0.8 V hysteresis, and oscillator using external RT/CT components. Its internal toggle flip-flop halves the oscillator frequency at the OUTPUT pin, limiting duty cycle to ≤50%-a defining distinction from UC3842/UC3843 variants.

It operates with a 5-V bandgap reference trimmed at the error amplifier input, supports automatic feedforward compensation via VFB, and uses ISENSE for primary-side current sensing with 3 V/V gain and 1 V maximum input. The totem-pole output stage sinks and sources up to 1 A peak current, optimized for direct N-MOSFET gate drive without external buffers.

Key Specifications

Pinout & Package

UC3845DTR is housed in an 8-pin SOIC (D) package measuring 4.90 mm × 6.00 mm, with gull-wing leads and standard JEDEC MS-012AC outline. Thermal resistance is R_θJA = 117.4°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC3844DTR and TL494CDR, UC3845DTR offers tighter UVLO hysteresis (0.8 V vs 3–6 V) and integrated current-mode control in a minimal 8-pin footprint-making it optimal for space-constrained, regulated-input DC-DC designs where simplicity and reliability are prioritized over topology flexibility.

Availability

UC3845DTR is available at Aetrix Electronics and suitable for industrial sensor power supplies, automotive telematics buck regulators, isolated flyback converters, and LED boost drivers requiring stable component supply across production lifecycles.

Supply support for UC3845DTR 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 delivering analog and embedded processing solutions, with leadership in power management ICs and industrial-grade controllers.

The UC384x product line was engineered specifically for cost-sensitive, high-reliability DC-DC and off-line switching power supplies-emphasizing minimal external component count, robust protection features, and thermal stability across commercial temperature ranges.

FAQ

What is the maximum switching frequency supported by UC3845DTR?

The UC3845DTR supports oscillator frequencies from 100 kHz to 500 kHz, set externally via RT and CT components. Its OUTPUT pin switches at half the oscillator frequency due to the internal toggle flip-flop, resulting in a practical PWM switching range of 50–250 kHz. This enables compact magnetics and efficient thermal design in DC-DC converters while maintaining stable current-mode control.

How does UC3845DTR differ from UC3842DTR in terms of duty cycle and UVLO?

The UC3845DTR has a maximum duty cycle of 47–50% and UVLO thresholds of 8.4 V (turn-on) and 7.6 V (turn-off), whereas UC3842DTR supports up to 100% duty cycle with 14.5–17.5 V / 8.5–11.5 V UVLO. These differences make UC3845DTR suitable for regulated DC-DC applications requiring limited conduction time, while UC3842DTR targets higher-duty-cycle off-line designs.

Can UC3845DTR drive a P-channel MOSFET directly?

No, UC3845DTR is optimized for N-channel MOSFET gate drive with its totem-pole OUTPUT stage that sources and sinks current but does not provide high-side floating bias. Driving a P-channel MOSFET would require level-shifting circuitry or an external high-side driver; the IC's OUTPUT is designed for low-side N-MOSFET configurations in buck, flyback, or boost topologies.

What is the purpose of the COMP pin on UC3845DTR, and how is it used in loop compensation?

On UC3845DTR, the COMP pin is the open-collector output of the internal error amplifier and serves as the control node for the feedback loop. External RC networks connected between COMP and GROUND-or COMP and VFB-set phase margin and crossover frequency. Forcing COMP to GROUND commands zero duty cycle, enabling soft-start or shutdown functionality without disabling the IC.

Does UC3845DTR include built-in overtemperature protection?

No, UC3845DTR does not integrate thermal shutdown circuitry. Protection relies on external design measures such as proper heatsinking, current limiting via ISENSE, and system-level thermal monitoring. Its absolute maximum junction temperature is 150°C, and thermal metrics (e.g., R_θJA = 117.4°C/W) guide PCB layout and airflow requirements to maintain safe operation within the 0°C to 70°C ambient range.