onsemi MC78M08BDT

Overview

MC78M08BDT from onsemi is a 500 mA, fixed +8.0 V positive linear voltage regulator in DPAK-3 (TO-252) package, featuring internal thermal shutdown, short-circuit current limiting, and safe-area compensation for rugged local on-card regulation. It delivers stable output across −40°C to +125°C with ±3% output voltage tolerance at 25°C and supports input voltages up to 35 V.

For engineers reviewing the MC78M08BDT datasheet, pinout, applications, or equivalent options, this device is selected for cost-sensitive, thermally constrained industrial power rails where simplicity, reliability, and automotive-grade temperature range are critical - especially when replacing TO-220 regulators with surface-mount footprint reduction.

Technical Context

The MC78M08BDT implements a monolithic three-terminal series pass architecture with built-in protection circuitry: thermal overload shutdown activates at ~150°C junction temperature, and short-circuit current limit holds peak output at ~350 mA under VI = 35 V. Its dropout voltage remains fixed at ~2.0 V across load and temperature.

Designed for fixed-output use without external components, it relies on internal bandgap reference and error amplifier feedback to maintain regulation. Input bias current is 3.2–6.0 mA, and ripple rejection reaches 56 dB at 120 Hz with 100 mA load - optimized for unregulated DC inputs derived from rectified AC or switching pre-regulators.

Key Specifications

Pinout & Package

DPAK-3 (TO-252) plastic surface-mount package with exposed thermal pad connected to Pin 2 (GND); case outline per onsemi CASE 369C, dimensions 6.10 × 6.54 × 2.28 mm, pitch 2.29 mm.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MC78M08CDTRKG, the MC78M08BDT trades ±2% initial accuracy for guaranteed −40°C startup capability; versus NCV78M08BDTRKG, it lacks automotive change control and PPAP documentation - making it ideal for cost-sensitive industrial designs needing wide temperature range without automotive certification overhead.

Availability

MC78M08BDT is available at Aetrix Electronics and suitable for industrial control systems, automotive body electronics, point-of-sale terminals, and legacy sensor interface modules requiring stable component supply across extended temperature ranges and multi-year production cycles.

Supply support for MC78M08BDT 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier delivering energy-efficient silicon solutions for automotive, industrial, cloud, medical, and IoT applications.

The MC78M00 series was designed as a compact, rugged, drop-in replacement for legacy 78xx regulators - targeting space-constrained PCBs in harsh environments where reliability, thermal resilience, and simplified design are paramount.

FAQ

What is the maximum input voltage rating for the MC78M08BDT?

The MC78M08BDT has an absolute maximum input voltage of 40 V for brief transients (≤100 ms), but its recommended continuous operating input range is 10.5 V to 23 V. Sustained operation above 35 V risks permanent damage due to internal junction breakdown - always verify input filtering and clamping in 24 V system designs.

Does the MC78M08BDT require an input bypass capacitor?

Yes, the MC78M08BDT requires a minimum 0.33 µF low-ESR capacitor (e.g., tantalum or ceramic) placed directly across Pins 1 and 2. This stabilizes high-frequency response and prevents oscillation, especially when input traces exceed 2 inches or when powered from switch-mode supplies with fast edge rates.

What is the thermal resistance (θ_JA) of the MC78M08BDT in standard PCB layout?

In a typical 1-inch² 2-oz copper pad layout, the MC78M08BDT exhibits θ_JA ≈ 92°C/W. With 2-inch² copper and thermal vias to inner layers, θ_JA improves to ~50°C/W. Its θ_JC is fixed at 5.0°C/W - meaning heatsink performance depends entirely on PCB thermal design, not package mounting.

Can the MC78M08BDT be used in adjustable output configurations?

No, the MC78M08BDT is a fixed +8.0 V output device with internal resistor divider; it cannot be adjusted. For variable outputs, use the LM317 or consider the MC78M00 series' adjustable variants like the MC78M00CDTG with external feedback - but note those require different pinouts and external components.

How does the MC78M08BDT handle short-circuit conditions?

Under short-circuit, the MC78M08BDT limits output current to ~350 mA and activates thermal shutdown if junction temperature exceeds ~150°C. Recovery is automatic once temperature drops below threshold - no latch-up or manual reset required. Peak short-circuit power dissipation is ~2.45 W at VI = 12 V.