STMicroelectronics L78L09ABUTR

Overview

L78L09ABUTR from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 9 V output at up to 100 mA, featuring internal current limiting, thermal shutdown, and short-circuit protection. It requires no external components, supports input voltages up to 30 V (for VO = 9 V), and operates across –40 °C to +125 °C junction temperature. It is used for local on-card regulation in industrial control modules, sensor signal conditioning circuits, and low-power microcontroller power rails.

For engineers reviewing the L78L09ABUTR datasheet, L78L09ABUTR pinout, L78L09ABUTR application, or L78L09ABUTR equivalent, this device serves as a drop-in replacement for Zener-diode/resistor regulators-offering lower quiescent current (6 mA typ.), improved line/load regulation (±150 mV max), and higher supply voltage rejection (37–44 dB).

Technical Context

The L78L09ABUTR employs monolithic bipolar technology with built-in thermal overload and short-circuit protection circuitry. Its architecture integrates a reference voltage generator, error amplifier, pass transistor, and protection logic-all within a single silicon die. No external capacitors are mandatory, though 0.33 µF input and 0.1 µF output ceramic capacitors are recommended per ST's test circuits.

It functions as a fixed-output series regulator with dropout voltage of 1.7 V (typ.) at 40 mA load and maintains stable regulation under varying line (VI = 11.5–23 V) and load (IO = 1–100 mA) conditions. Output voltage tolerance is ±4% over temperature (–40 °C to +125 °C), confirmed by AB-grade qualification.

Key Specifications

Pinout & Package

Supplied in SOT-89 package: compact surface-mount outline with exposed thermal pad (pin 2 connected to tab/heat sink). Pin 1 = Input, Pin 2 = Ground, Pin 3 = Output. The tab is electrically connected to ground and must be soldered to ≥1 cm² PCB copper area for optimal thermal performance (R_thJA = 55 °C/W max).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L09ACZ and MC78L09ACP, the L78L09ABUTR provides wider operating temperature range (–40 °C to +125 °C), tighter output tolerance (±4%), superior thermal performance via SOT-89 thermal pad, and guaranteed specification compliance across full industrial temperature extremes.

Availability

L78L09ABUTR is available at Aetrix Electronics and suitable for industrial sensor interface, microcontroller power rail, programmable logic controller (PLC) I/O module, and medical diagnostic handheld applications requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for L78L09ABUTR 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, MCU, power, and sensing solutions for industrial, automotive, and consumer markets.

The L78L series belongs to ST's legacy linear regulator product line, engineered specifically for robust, low-cost, no-frills fixed-voltage regulation in harsh environments-emphasizing reliability, thermal resilience, and ease of integration without external compensation.

FAQ

What is the minimum input voltage required for regulation at full 100 mA load?

The L78L09ABUTR requires a minimum input voltage of 10.7 V to maintain 9 V output under 100 mA load, based on its 1.7 V typical dropout voltage. At higher temperatures or worst-case process corners, design margin should include up to 2.0 V dropout, recommending ≥11.0 V minimum input for robust operation.

Can this regulator be used with ceramic output capacitors?

Yes-ST specifies 0.1 µF ceramic capacitors for output stabilization, and the L78L09ABUTR is stable with X7R or X5R types. Unlike older 78xx variants, it does not require ESR-based damping, eliminating the need for tantalum or aluminum electrolytic capacitors.

Is the SOT-89 thermal pad electrically connected, and how should it be handled on the PCB?

The SOT-89 tab (pin 2) is internally connected to ground. It must be soldered to a dedicated PCB copper pour ≥1 cm², thermally connected to inner-layer ground planes via ≥4 thermal vias (0.3 mm diameter), to achieve the rated R_thJA of 55 °C/W and prevent thermal shutdown at >60 mA continuous load.

How does the AB grade differ from AC grade in practical design use?

The AB grade guarantees ±4% output voltage accuracy over –40 °C to +125 °C junction temperature, while AC grade is specified only from 0 °C to +70 °C with ±5% tolerance. For automotive engine control, industrial motor drives, or outdoor infrastructure, AB grade ensures regulation remains within spec across full environmental stress profiles.