Texas Instruments UC3843D8TRG4

Overview

UC3843D8TRG4 from Texas Instruments is a fixed-frequency current-mode PWM controller IC designed for DC-DC converter applications, featuring 8.4 V turn-on/7.6 V turn-off UVLO thresholds, up to 500 kHz switching frequency, 100% maximum duty cycle, and ±1 A peak totem-pole output drive capability. It operates across 0°C to 70°C and integrates an internally trimmed 5-V reference, error amplifier, and pulse-by-pulse current limiting.

For engineers reviewing the UC3843D8TRG4 datasheet, UC3843D8TRG4 pinout, UC3843D8TRG4 application, or UC3843D8TRG4 equivalent, key selection criteria include its low-startup-current (<1 mA) operation, compatibility with N-channel MOSFET gate driving, and suitability for regulated-input isolated/non-isolated DC-DC topologies requiring stable current-mode control without external slope compensation.

Technical Context

The UC3843D8TRG4 implements a current-mode control architecture with a dedicated ISENSE input that directly terminates OUTPUT conduction via a PWM comparator, enabling precise per-cycle current limiting. Its oscillator uses RT/CT pin with external R–C network to set frequency (f_OSC = 1.72 / R_RTC_CT), and its error amplifier features 90 dB open-loop gain and 1 MHz unity-gain bandwidth for robust loop compensation.

UVLO hysteresis (0.8 V) and automatic feedforward compensation support stable startup and line regulation in DC-DC systems with tightly regulated input rails. The device lacks internal toggle flip-flop logic-unlike UC3844/UC3845-enabling full 0–100% duty cycle operation without frequency halving.

Key Specifications

Pinout & Package

UC3843D8TRG4 is housed in an 8-pin SOIC (D package), 4.90 mm × 6.00 mm body size, with gull-wing leads and standard JEDEC MS-012AC footprint.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC3842D8TRG4 and TL494CDR, UC3843D8TRG4 delivers optimal integration for regulated-input DC-DC converters-combining low-threshold UVLO, full-duty-cycle capability, and hardware current limiting in a single 8-pin SOIC, reducing BOM count and layout complexity.

Availability

UC3843D8TRG4 is available at Aetrix Electronics and suitable for isolated DC-DC converters, non-isolated buck regulators, and constant-current LED drivers requiring stable component supply and long-term production continuity.

Supply support for UC3843D8TRG4 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 delivering analog, embedded processing, and connectivity solutions with emphasis on reliability, precision, and power efficiency.

The UC384x product line was engineered specifically for cost-sensitive, high-volume DC-DC and off-line power supply applications-prioritizing minimal external component count, robust protection, and seamless integration with N-channel MOSFETs.

FAQ

What is the UVLO behavior of UC3843D8TRG4 and how does it affect system startup?

The UC3843D8TRG4 features undervoltage lockout with 8.4 V turn-on and 7.6 V turn-off thresholds, providing 0.8 V hysteresis. This ensures clean, bounce-free startup from regulated DC sources like 12 V or 5 V rails. During operation, if input drops below 7.6 V, UC3843D8TRG4 disables OUTPUT and enters low-current standby until voltage recovers above 8.4 V-preventing erratic switching during brownout conditions.

Can UC3843D8TRG4 drive a MOSFET directly, and what are the gate drive limitations?

Yes, UC3843D8TRG4 can directly drive N-channel MOSFETs via its ±1 A peak totem-pole OUTPUT stage. It supports gate charges up to ~50 nC at 400 kHz without external buffering. However, for MOSFETs with Q_g > 50 nC or operation above 300 kHz, a discrete gate driver is recommended to maintain fast edge rates and reduce switching losses. Always include a 10–100 Ω series gate resistor and Schottky clamp diodes for overshoot suppression.

How is the switching frequency set on UC3843D8TRG4, and what tolerance should be expected?

Switching frequency is set externally using resistor R_RT from VREF to RT/CT and capacitor C_CT from RT/CT to GROUND, per f_OSC = 1.72 / (R_RT × C_CT). At 25°C with 1% R and 5% C components, typical frequency tolerance is ±8%. The UC3843D8TRG4's oscillator exhibits ±5% temperature stability over 0°C–70°C, and voltage stability is ±1% across 12–25 V VCC range.

Does UC3843D8TRG4 support voltage-mode control, and if so, how is it implemented?

Yes, UC3843D8TRG4 supports voltage-mode control by applying a sawtooth ramp signal to the ISENSE pin, overriding its default current-sense function. This ramp-typically derived from the RT/CT node or a dedicated oscillator-injects slope compensation to stabilize duty cycles >50% in boost or flyback topologies. The internal current-sense comparator remains active but is effectively reconfigured as a PWM comparator with external timing reference.

What is the role of the COMP pin in UC3843D8TRG4, and how should it be compensated?

The COMP pin is the open-collector output of the UC3843D8TRG4's error amplifier and serves as the control node for loop compensation. It must be connected to VFB via a Type II (capacitor + RC) or Type III (dual-pole, dual-zero) network to ensure phase margin >45° and gain margin >10 dB. The amplifier's 90 dB gain and 1 MHz bandwidth allow stable compensation up to ~100 kHz crossover; avoid placing large capacitors directly from COMP to GROUND without series resistance to prevent instability.