STMicroelectronics L78M08ACDT

Overview

L78M08ACDT from STMicroelectronics is a fixed-output +8 V, 500 mA positive linear voltage regulator in DPAK package, featuring ±2 % output voltage tolerance at 25 °C, thermal overload protection, short-circuit current limiting, and safe operating area (SOA) protection. It delivers stable local regulation for microcontroller power rails, sensor interfaces, and industrial control modules where input-to-output differential voltage exceeds 2 V.

For engineers reviewing the L78M08ACDT datasheet, L78M08ACDT pinout, L78M08ACDT application, or L78M08ACDT equivalent, key selection criteria include guaranteed 0–125 °C operating junction temperature range, 80 mV load regulation (5–200 mA), 30 mV line regulation (11–25 V), 56 dB supply voltage rejection at 120 Hz, and 52 µV RMS output noise (10 Hz–100 kHz).

Technical Context

The L78M08ACDT implements a monolithic three-terminal series pass architecture with internal PNP transistor, current-limiting circuitry, and thermal shutdown trigger at ~165 °C. Its SOA protection dynamically reduces short-circuit current as pass transistor V_CE increases, preventing second breakdown during sustained overload.

Designed for fixed-voltage operation, it requires no external components for basic functionality but supports adjustable output via external resistive networks per Figure 18. Input bypass capacitor (≥0.33 µF tantalum/mylar) is recommended for stability with long trace lengths or large output capacitance.

Key Specifications

Pinout & Package

The L78M08ACDT is housed in a surface-mount DPAK (TO-252) package with exposed thermal pad, optimized for PCB heat dissipation (R_thJA = 100 °C/W, R_thJC = 8 °C/W). Pin 1 is Input, Pin 2 is Ground, Pin 3 is Output.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2940CT-8.0/NOPB, L78M08ACDT offers tighter tolerance and lower noise but lower current and higher dropout; versus MC78M08CDTG, it provides superior accuracy and thermal stability in the 0–125 °C band at identical current capability.

Availability

L78M08ACDT is available at Aetrix Electronics and suitable for industrial PLC I/O modules, automotive body control units, medical sensor interfaces, and point-of-sale terminal power management requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for L78M08ACDT 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 silicon solutions for automotive, industrial, and consumer markets since 1987.

The L78Mxx series belongs to ST's legacy linear regulator product line, engineered for robustness and simplicity in cost-sensitive, non-automotive industrial and embedded applications where reliability under thermal and electrical stress is prioritized over ultra-low quiescent current or ultra-low dropout.

FAQ

What is the maximum allowable input voltage for L78M08ACDT?

The absolute maximum DC input voltage is 40 V for output voltages ≥20 V, but for L78M08ACDT (8 V output), the datasheet specifies 35 V as the absolute maximum input voltage. Operation above 23 V is not recommended for reliable regulation, as dropout voltage remains fixed at 2 V and internal power dissipation rises quadratically with (VI – 8 V) × IO.

Does L78M08ACDT require input and output capacitors?

Yes - an input bypass capacitor ≥0.33 µF (tantalum or low-ESR ceramic) is strongly recommended to ensure stability with long PCB traces or high-impedance sources, and a 0.1 µF ceramic output capacitor improves transient response and phase margin. Omitting either may cause oscillation or poor load-step recovery per Figure 14.

Can L78M08ACDT be used in adjustable-voltage configurations?

Yes - per Figure 18 in the datasheet, it can be configured as an adjustable regulator using two external resistors to set VO = 7.0–20 V, provided VI – VO ≥ 2.0 V. The ADJ pin is not present; adjustment is achieved by elevating the ground reference with a resistor divider, converting the fixed regulator into a floating reference topology.

How does thermal protection behave during sustained overload?

When junction temperature exceeds ~165 °C, thermal shutdown activates, cutting output current to near zero until die cools by ~20 °C. During overload below shutdown threshold, SOA protection progressively reduces short-circuit current as V_CE increases - e.g., Isc drops from 250 mA at V_CE = 2 V to <100 mA at V_CE = 10 V - preventing second breakdown in the pass transistor.