onsemi KA78R09CTSTU

Overview

KA78R09CTSTU from ON Semiconductor is a 1A, 9V fixed-output low-dropout linear voltage regulator in TO-220F-4L package with output disable control, thermal shutdown, and short-circuit protection. It delivers stable 9V power with ≤0.5V dropout at full load and supports industrial temperature range (−20°C to +80°C), commonly used in embedded power rails for microcontrollers and analog circuitry.

For engineers reviewing the KA78R09CTSTU datasheet, pinout, applications, or equivalent options, key selection criteria include its 9V ±2.2% output tolerance, disable-function compatibility with 0.8V/2.0V logic thresholds, 45–55 dB ripple rejection, and TO-220F-4L thermal performance (R_θJC = 4.31°C/W).

Technical Context

The KA78R09CTSTU integrates bandgap reference, SOA protection, overvoltage detection, and thermal shutdown circuitry within a single silicon die. Its internal pass transistor operates in linear mode with current-limited peak output up to ~2.75A under transient overload conditions.

It features active output disable via pin 4 (V_dis), where logic-low (<0.8V) disables the output and reduces quiescent current to <0.4mA, while logic-high (>2.0V) enables regulation. Input-to-output differential voltage must remain ≥1.0V for stable operation per typical performance curves.

Key Specifications

Pinout & Package

KA78R09CTSTU uses the TO-220F-4L full-mold package with 4 leads and integrated heat slug. The package is lead-free and RoHS-compliant, with thermal pad designed for mechanical mounting to heatsinks.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2940CT-9.0/NOPB and TLV1117-9.0, KA78R09CTSTU uniquely combines 1 A capability, 0.5 V dropout, disable control, and TO-220F-4L thermal performance-making it optimal for industrial modules requiring both robustness and power sequencing.

Availability

KA78R09CTSTU is available at Aetrix Electronics and suitable for industrial automation, automotive electronics, and test equipment requiring stable component supply with long-term lifecycle assurance.

Supply support for KA78R09CTSTU 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 is a global semiconductor manufacturer specializing in power management, analog, and sensor solutions for automotive, industrial, and cloud infrastructure markets.

The KA78RXXC series was designed as a drop-in upgrade to legacy 78xx regulators-adding disable control, tighter tolerance, and improved thermal performance for modern embedded power systems.

FAQ

What is the minimum input voltage required for KA78R09CTSTU to regulate 9 V output?

The KA78R09CTSTU requires a minimum input voltage of 10 V to maintain regulation at full 1 A load, based on its maximum 0.5 V dropout specification. At lighter loads, input can be reduced-per Figure 1 in the datasheet, regulation holds down to ~9.5 V at 500 mA. Always verify margin under worst-case temperature and line conditions using the actual KA78R09CTSTU electrical characteristics table.

Does KA78R09CTSTU require an external heatsink for 1 A continuous operation?

Yes-KA78R09CTSTU dissipates up to 3 W at 12 V input (12 V − 9 V × 1 A = 3 W). With R_θJC = 4.31°C/W and max T_J = 150°C, a heatsink is mandatory to keep junction temperature within limits at ambient >50°C. The datasheet specifies P_d2 = 15 W with heatsink vs. only 1.5 W without, confirming thermal design dependency on external heatsinking for KA78R09CTSTU.

Can KA78R09CTSTU be used in parallel to increase output current?

No-KA78R09CTSTU is not designed for parallel operation. Its output voltage tolerance (±2.2%) and lack of current-sharing circuitry would cause unequal load distribution and possible thermal runaway. For higher current, select a single higher-rated LDO or switcher solution; do not attempt paralleling multiple KA78R09CTSTU units.

What is the purpose of the V_dis pin on KA78R09CTSTU, and how should it be driven?

The V_dis pin (pin 4) controls output enable/disable: applying <0.8 V disables the output and reduces quiescent current to <0.4 mA; applying >2.0 V enables regulation. It accepts standard TTL/CMOS logic levels-no external pull-up or driver needed. In most designs, connect V_dis to MCU GPIO or system enable signal; leave floating only if always-on operation is intended. This function is integral to KA78R09CTSTU's power management capability.

Is KA78R09CTSTU compatible with legacy 7809-style footprints?

No-KA78R09CTSTU uses the TO-220F-4L package with 4 pins (Vin, Vo, GND, V_dis), whereas standard 7809 devices use 3-pin TO-220 (Vin, GND, Vo). The fourth pin and re-ordered pinout (1:Vin, 2:Vo, 3:GND, 4:V_dis) make KA78R09CTSTU incompatible with 3-pin layouts. PCB redesign is required to accommodate KA78R09CTSTU's pin configuration and disable functionality.