STMicroelectronics L78L09ACUTR

Overview

L78L09ACUTR from STMicroelectronics is a fixed +9 V, 100 mA positive voltage regulator in SOT-89 package with ±4% output tolerance, 1.7 V dropout voltage, thermal overload and short-circuit protection, and no external components required - used for local on-card regulation in industrial control power rails.

For engineers reviewing the L78L09ACUTR datasheet, L78L09ACUTR pinout, L78L09ACUTR application, or L78L09ACUTR equivalent, key selection factors include output accuracy (±4%), low quiescent current (6 mA typ.), noise performance (70 µV RMS), supply rejection (37–44 dB), and thermal resistance (55 °C/W junction-to-ambient).

Technical Context

The L78L09ACUTR employs monolithic silicon construction with internal current limiting, thermal shutdown, and safe-area protection - enabling robust operation without external compensation. Its architecture delivers stable DC output under varying load (1–100 mA) and input voltage (11.5–23 V) conditions while maintaining tight regulation.

It operates across 0 to 125 °C junction temperature range and supports PCB heat-sinking via the exposed die-attach flag in the SOT-89 package. The device functions as a drop-in replacement for Zener-diode/resistor regulators, offering lower noise, reduced quiescent current, and guaranteed short-circuit survival.

Key Specifications

Pinout & Package

SOT-89 package with three terminals: Input (Pin 1), Ground (Pin 2), Output (Pin 3). Pins 2, 3, 6, and 7 are internally connected to the die-attach flag for enhanced thermal conduction - requires minimum 6 cm² copper area on PCB for rated power dissipation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-voltage linear regulator applications.

Compared with LM78L09ACZ/NOPB, L78L09ACUTR provides tighter output tolerance and superior thermal performance in SOT-89; versus TL78L09ACDR, it trades package size for lower cost and proven field reliability in space-constrained industrial modules.

Availability

L78L09ACUTR is available at Aetrix Electronics and suitable for industrial automation, medical instrumentation, and automotive body electronics requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for L78L09ACUTR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, power, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The L78L series belongs to ST's legacy linear regulator product line, engineered for cost-sensitive, high-reliability applications where simplicity, ruggedness, and long-term availability outweigh programmability or ultra-low IQ requirements.

FAQ

What is the minimum input voltage required for stable 9 V output?

The L78L09ACUTR requires a minimum input voltage of 10.7 V to maintain regulation at full 100 mA load, based on its 1.7 V dropout specification. At lighter loads (e.g., 40 mA), input can be as low as 10.7 V; for worst-case tolerance and temperature drift, 11.5 V is recommended per datasheet test conditions.

Can this regulator be used in parallel to increase output current?

No - the L78L09ACUTR lacks built-in current-sharing capability and has no output offset trimming. Paralleling units causes unequal current distribution due to output voltage tolerance mismatch (±4%), risking thermal runaway in one device. Use a single higher-current regulator or external pass transistor instead.

Is an input capacitor mandatory for stable operation?

Yes - ST recommends a minimum 0.33 µF ceramic capacitor at the input pin, placed within 1 cm of the device. This suppresses high-frequency noise and prevents oscillation caused by source impedance interacting with internal compensation. Omission risks instability under fast load transients.

Does the SOT-89 package require soldering to a thermal pad on the PCB?

Yes - Pin 2 (Ground) and the exposed die-attach flag are electrically and thermally connected. For rated 100 mA operation, ST specifies ≥6 cm² of 2-oz copper connected directly to Pin 2 via multiple thermal vias. Without this, thermal resistance rises to 200 °C/W, limiting usable current to ~25 mA.