onsemi MC78M08CDTX

Overview

MC78M08CDTX from Fairchild Semiconductor is a three-terminal fixed-output positive voltage regulator delivering 8 V at up to 0.5 A, featuring thermal overload protection, short-circuit protection, and SOA-protected output transistor. It operates across 0–150°C junction temperature and supports input voltages from 10.5 V to 23 V in standard applications-commonly used in industrial power supplies and embedded system bias rails.

For engineers reviewing the MC78M08CDTX datasheet, pinout, applications, or equivalent options, key selection criteria include dropout voltage (2 V @ 500 mA), load regulation (≤160 mV over 5 mA–0.5 A), ripple rejection (80 dB @ 120 Hz), output voltage accuracy (±4% at +25°C), and D-PAK package thermal resistance (92 °C/W).

Technical Context

The MC78M08CDTX implements a classic series-pass linear regulator architecture with internal reference voltage, error amplifier, and current-limited series pass element. Protection circuitry includes dedicated thermal shutdown and safe operating area (SOA) monitoring for the output transistor.

It requires minimal external components: 0.33 µF input capacitor (CI) and 0.1 µF output capacitor (CO) for stability and transient response. No feedback network is needed-output voltage is factory-trimmed to 8 V with ±4% tolerance over full load and temperature range.

Key Specifications

Pinout & Package

D-PAK (TO-252) surface-mount package with exposed thermal pad; footprint compatible with JEDEC MO-247, optimized for PCB heat dissipation via copper pour under pad.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MC78M08CDTX, LM78M08CDT offers identical performance with enhanced long-term availability, while MC78M08CT trades surface-mount convenience for improved thermal handling in discrete heatsinked implementations.

Availability

MC78M08CDTX is available at Aetrix Electronics and suitable for industrial control systems, embedded microcontroller bias rails, and legacy system retrofits requiring stable component supply and guaranteed long-term sourcing.

Supply support for MC78M08CDTX 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

Fairchild Semiconductor was a leading analog and power IC manufacturer, acquired by ON Semiconductor in 2016; its legacy linear regulator portfolio remains widely deployed and supported.

The MC78MXX series was designed specifically for cost-sensitive, high-reliability industrial and automotive-adjacent applications requiring fixed-output, thermally robust, three-terminal regulators with integrated protection.

FAQ

What is the maximum input voltage rating for MC78M08CDTX?

The absolute maximum input voltage for MC78M08CDTX is 40 V for the 24 V output variant, but for the 8 V version, the datasheet specifies 23 V maximum under normal operating conditions (VI = 10.5 V to 23 V). Exceeding 23 V risks exceeding safe SOA limits and triggering thermal shutdown-always maintain ≥2 V headroom above output voltage for stable regulation. The MC78M08CDTX must never be operated beyond its rated input range to ensure long-term reliability.

Does MC78M08CDTX require an input capacitor, and if so, what value?

Yes, MC78M08CDTX requires a 0.33 µF ceramic input capacitor (CI) placed as close as possible to the input pin, per the official Fairchild datasheet. This capacitor stabilizes the regulator against source impedance and prevents oscillation during transient load changes. Omitting CI may cause instability or voltage overshoot, especially when the regulator is located >2 inches from the bulk filter capacitor. The MC78M08CDTX design assumes this capacitor is present for all specified performance metrics.

Can MC78M08CDTX be used in adjustable-output configurations?

No-MC78M08CDTX is a fixed-output device with internal feedback resistors trimmed to 8 V; it lacks an adjust (ADJ) pin or external feedback capability. While application note figures show methods using external op-amps (e.g., LM741) to create adjustable outputs, those circuits replace the MC78M08CDTX function entirely and do not modify its internal regulation. For true adjustability, use LM317 or similar variable regulators-not MC78M08CDTX.

What is the thermal resistance of MC78M08CDTX in its D-PAK package?

The MC78M08CDTX in D-PAK (TO-252) package has a junction-to-air thermal resistance (R_θJA) of 92 °C/W under JEDEC-standard test conditions (76.2 mm × 114.3 mm × 1.6 mm board, no airflow). This value assumes the thermal pad is soldered to a minimum 1-inch² copper pour. Without proper thermal land, actual R_θJA degrades significantly-so PCB layout directly determines real-world thermal performance of the MC78M08CDTX.

Is MC78M08CDTX RoHS compliant and lead-free?

Yes, MC78M08CDTX is RoHS compliant and lead-free, consistent with Fairchild's post-2006 manufacturing standards and ON Semiconductor's continued compliance program. The D-PAK package uses matte tin (Sn) lead finish, and the device meets JEDEC J-STD-609 Category 1 marking requirements. Full compliance documentation-including substance declarations and test reports-is available upon request for MC78M08CDTX for aerospace, medical, and industrial certification workflows.