onsemi KA78R33CTSTU

Overview

KA78R33CTSTU from ON Semiconductor is a 1A, 3.3V fixed-output low-dropout linear voltage regulator in TO-220F-4L package with output disable control, thermal shutdown, and overcurrent protection. It delivers stable 3.3V power for microcontroller core supplies, industrial sensors, and embedded logic rails where input-to-output differential is constrained.

For engineers reviewing the KA78R33CTSTU datasheet, pinout, applications, or equivalent options, key selection criteria include dropout voltage ≤0.5V at 1A, disable function threshold (V_disH ≥2.0V), ±2.4% output voltage tolerance, and TO-220F-4L thermal resistance (R_θJC = 4.31°C/W).

Technical Context

The KA78R33CTSTU integrates bandgap reference, SOA protection, overvoltage detection, and high/low-level output enable logic. Its internal pass transistor operates in linear mode with peak current limiting and thermal foldback to prevent damage under overload or elevated junction temperature.

It supports input voltages from 4V to 10V (per datasheet Note 3 & 4) and maintains regulation across –20°C to +80°C ambient. The V_dis terminal accepts TTL/CMOS-compatible logic levels to actively disable output with <20μA bias current when high and –0.4mA sink when low.

Key Specifications

Pinout & Package

TO-220F-4L full-mold plastic package with isolated tab (non-conductive mounting surface), 4-pin vertical lead frame, and industry-standard footprint for mechanical mounting and heatsinking.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-output LDO regulator applications.

Compared with LM2931T-3.3/NOPB and TLV1117-33IDCYR, KA78R33CTSTU uniquely combines 1A current, 0.5V dropout, and digital disable in TO-220F-4L-enabling robust, sequenced 3.3V power delivery where thermal headroom and control flexibility are critical.

Availability

KA78R33CTSTU is available at Aetrix Electronics and suitable for industrial sensor nodes, embedded microcontroller core supplies, and USB peripheral power management requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for KA78R33CTSTU 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

ON Semiconductor (formerly Fairchild Semiconductor) is a global semiconductor manufacturer specializing in power management, analog, and discrete devices for automotive, industrial, and cloud infrastructure markets.

The KA78RXXC series was designed as a drop-in upgrade to legacy 78xx regulators, adding low-dropout operation, disable control, and enhanced protection for modern embedded systems demanding higher efficiency and smarter power control.

FAQ

What is the maximum input voltage for KA78R33CTSTU?

The absolute maximum input voltage for KA78R33CTSTU is 35V, but its recommended operating input range is 4V to 10V per datasheet Note 3 and 4. Exceeding 10V increases power dissipation and thermal stress without functional benefit, as the regulator is optimized for low-headroom 3.3V generation. Always verify input ripple and transient spikes remain within this window in final designs using KA78R33CTSTU.

Does KA78R33CTSTU require an external output capacitor?

Yes, KA78R33CTSTU requires a minimum 47μF output capacitor (Co) for stability and transient response, as specified in the Typical Application circuit. Aluminum or tantalum capacitors are acceptable; ceramic capacitors may be used in parallel but must not replace the bulk capacitance. Omitting Co risks oscillation and poor load-step recovery, directly impacting system reliability when using KA78R33CTSTU in real-world applications.

How does the disable function of KA78R33CTSTU work?

The Vdis pin on KA78R33CTSTU controls output state: applying ≥2.0V (V_disH) enables regulation, while ≤0.8V (V_disL) disables output with fast turn-off (<10μs). Bias current is ≤20μA when high and ≤–0.4mA when low, allowing direct interfacing with 3.3V GPIOs. This feature enables precise power sequencing and zero-load standby-key advantages of KA78R33CTSTU over non-disable LDOs.

What thermal performance can be expected from KA78R33CTSTU at 1A load?

With a heatsink, KA78R33CTSTU supports 15W power dissipation (Pd2), corresponding to ~15°C/W total thermal resistance. At 1A and 6.5V input (3.2V dropout), power dissipation is ~3.2W-resulting in ~48°C junction rise above case. Using its R_θJC = 4.31°C/W, junction temperature stays well below 150°C limit even at +80°C ambient, confirming KA78R33CTSTU's suitability for continuous 1A operation in industrial environments.

Is KA78R33CTSTU pin-compatible with standard 7805-style TO-220 regulators?

No, KA78R33CTSTU uses TO-220F-4L (4-pin) packaging with pinout Vin–Vo–GND–Vdis, unlike 3-pin 78xx regulators (Vin–GND–Vo). The fourth pin (Vdis) adds disable functionality but requires PCB layout revision. Direct replacement is not possible without schematic and footprint changes-engineers must allocate space and routing for the Vdis signal when migrating to KA78R33CTSTU from legacy parts.