Texas Instruments UC2842ANG4

Overview

UC2842ANG4 from Texas Instruments is a current-mode PWM controller IC designed for off-line and DC-DC switch-mode power supplies. It features 500 kHz maximum switching frequency, <0.5 mA start-up current, 8.3 mA trimmed oscillator discharge current, undervoltage lockout with 16 V turn-on/10 V turn-off hysteresis, and a 1 A totem-pole output stage driving MOSFET gates directly in flyback, forward, and boost topologies.

For engineers reviewing the UC2842ANG4 datasheet, UC2842ANG4 pinout, UC2842ANG4 application, or UC2842ANG4 equivalent, key selection criteria include peak-current-mode control capability, UVLO thresholds optimized for AC-input PSUs, pulse-by-pulse current limiting, internal 5 V reference accuracy (±1%), and compatibility with TI's WEBENCH® Power Designer for custom SMPS design.

Technical Context

The UC2842ANG4 implements fixed-frequency peak-current-mode control using an internal error amplifier (80 dB open-loop gain, 1 MHz unity-gain bandwidth), a current-sense comparator clamping input at 1 V, and a programmable oscillator driven by RT/CT pins. Its architecture enables cycle-by-cycle current limiting and automatic feedforward compensation for improved line regulation.

During undervoltage lockout (UVLO), the device draws only 0.3–0.5 mA and forces OUTPUT low while sinking ≥10 mA at ≤1.2 V - preventing parasitic MOSFET turn-on via Miller effect. The 1-A totem-pole output supports direct gate drive of power FETs without external buffers.

Key Specifications

Pinout & Package

UC2842ANG4 is supplied in an 8-pin PDIP (Plastic Dual In-line Package) with 9.81 mm × 9.43 mm footprint and through-hole mounting.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC3842N and TL494CN, UC2842ANG4 delivers superior current-mode control fidelity, tighter UVLO hysteresis for AC-line stability, and lower start-up current for high-voltage bias networks - making it optimal for cost-sensitive, high-reliability off-line SMPS where peak-current sensing is mandatory.

Availability

UC2842ANG4 is available at Aetrix Electronics and suitable for AC-DC adapters, industrial power modules, and battery-operated DC-DC converters requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for UC2842ANG4 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 design tools.

The UCx84xA product line was engineered specifically for cost-effective, high-efficiency current-mode switch-mode power supplies - targeting off-line AC-DC conversion, isolated DC-DC modules, and industrial power systems demanding robust UVLO and precise current limiting.

FAQ

What is the maximum operating frequency of the UC2842ANG4?

The UC2842ANG4 supports a maximum oscillator frequency of 500 kHz, as specified in the Recommended Operating Conditions section of its datasheet. This frequency is set externally via the RT/CT pins and enables high-power-density designs with smaller magnetic components and output filters. Operation beyond 500 kHz is not guaranteed and may degrade pulse-width accuracy or thermal performance. The UC2842ANG4 maintains stable current-mode control and full feature functionality up to this rated limit.

Does the UC2842ANG4 require an external current-sense resistor?

Yes, the UC2842ANG4 requires an external current-sense resistor connected between the power switch source and ground. The voltage developed across this resistor is fed into the ISENSE pin, where the internal comparator triggers at 1 V to enforce pulse-by-pulse current limiting. Typical values range from 0.1 Ω to 1 Ω depending on peak current requirements. No internal sense element exists - the resistor is mandatory for overcurrent protection and proper current-mode operation of the UC2842ANG4.

What is the purpose of the VREF pin on the UC2842ANG4?

The VREF pin on the UC2842ANG4 provides a stable, internally trimmed 5.0 V ±1% reference voltage output, rated for up to 10 mA load. It serves three critical functions: biasing the optocoupler LED in isolated feedback loops, setting the threshold for the error amplifier's FB input, and supplying reference voltage to external circuitry such as voltage dividers or comparators. A 1 µF ceramic capacitor must be placed directly at the VREF pin to ensure high-frequency noise immunity and loop stability in the UC2842ANG4 system.

Can the UC2842ANG4 operate without an external RT/CT network?

No, the UC2842ANG4 cannot operate without an external RT/CT network. The oscillator function relies entirely on the resistor (RT) connected between VREF and the RT/CT pin, and the capacitor (CT) connected between RT/CT and ground. These components define both the oscillator frequency and maximum duty cycle. Omitting either component results in no internal clock signal, causing the UC2842ANG4 to remain in UVLO or produce no gate drive output. TI recommends RT = 5–100 kΩ and CT = 470 pF–4.7 nF for reliable UC2842ANG4 operation.

How does the UC2842ANG4 handle undervoltage lockout during power-up?

During power-up, the UC2842ANG4 remains in undervoltage lockout (UVLO) until VCC reaches 16 V. While in UVLO, it draws only 0.3–0.5 mA and forces the OUTPUT pin low while sinking ≥10 mA at ≤1.2 V - actively preventing parasitic turn-on of the external MOSFET due to Miller capacitance. Once VCC exceeds 16 V, the internal 5 V reference stabilizes and normal PWM operation begins. If VCC drops below 10 V during operation, UVLO re-engages and OUTPUT goes low again. This behavior is intrinsic to the UC2842ANG4 and requires no external circuitry.