LM309K 5V Voltage Regulator Technical Summary

Overview

The LM309K is a member of the LM109 series of fixed-voltage regulators, providing a complete 5V voltage regulation solution on a single silicon chip. Designed primarily for local regulation in digital systems, this component addresses voltage distribution challenges associated with centralized power regulation schemes. The device offers excellent line and load regulation characteristics, making it suitable for demanding applications where stable 5V power is critical.

Manufactured using monolithic integrated circuit technology, the LM309K combines reference voltage source, error amplifier, series pass transistor, and current limiting circuitry in one robust package. The regulator features internal thermal shutdown protection and safe-area compensation, enhancing system reliability under fault conditions.

Key Features

• Fixed 5V output voltage with ±4% tolerance
• Output current capability up to 200mA (TO-5 package)
• Internal thermal overload protection
• Internal short-circuit current limiting
• Specified compatibility with TTL and DTL logic families
• Low output impedance (typically 0.05Ω)
• Wide input voltage range (7V to 35V)
• No external components required for basic operation
• Available in rugged TO-5 (K package) and TO-3 metal can packages

Applications

The LM309K finds extensive use in various electronic systems requiring stable 5V power:

Digital Systems

• Point-of-load regulation for TTL and DTL logic circuits
• Microprocessor and microcontroller power supplies
• Memory subsystem voltage regulation
• Interface circuit power management

Industrial Electronics

• Control system power supplies
• Sensor interface circuits
• Instrumentation power conditioning
• Test equipment voltage regulation

Consumer Electronics

• Set-top boxes
• Gaming consoles
• Audio/video equipment
• Home automation systems

Embedded Systems

• Single-board computers
• Industrial controllers
• Automotive electronics
• Medical monitoring devices

Electrical Characteristics

All specifications are given for TJ = 25°C, IO = 200mA, VI = 10V, and CI = 0.1μF unless otherwise noted.

Absolute Maximum Ratings

• Input Voltage: 35V
• Power Dissipation: Internally Limited
• Operating Junction Temperature Range: 0°C to +125°C
• Storage Temperature Range: -65°C to +150°C
• Lead Temperature (Soldering, 10 sec): 300°C

Electrical Specifications

• Output Voltage: 4.8V to 5.2V (5V ±4%)
• Line Regulation: 10mV (VI = 7V to 25V)
• Load Regulation: 30mV (IO = 5mA to 200mA)
• Quiescent Current: 5mA (typical)
• Output Noise Voltage: 40μV (10Hz to 100kHz)
• Ripple Rejection: 65dB (120Hz)
• Dropout Voltage: 2V (IO = 200mA)
• Short-Circuit Current: 300mA (typical)
• Thermal Resistance, Junction-to-Case: 5°C/W (TO-5 package)

Package Information

The LM309K is available in two robust package options:

TO-5 Metal Can Package (K Suffix)

• Package Dimensions: 8.6mm diameter, 6.3mm height (excluding leads)
• Lead Material: Kovar with gold plating
• Terminal Configuration:
  • Pin 1: Input
  • Pin 2: Ground
  • Pin 3: Output
• Weight: 1.2 grams (approximate)
• Mounting: Through-hole with optional heatsink attachment

TO-3 Power Package

• Package Dimensions: 22.1mm x 15.9mm x 10.7mm
• Case Material: Steel with nickel plating
• Terminal Configuration:
  • Case: Ground
  • Pin 1: Input
  • Pin 2: Output
• Weight: 11 grams (approximate)
• Mounting: Requires heatsink for full power capability

Thermal Considerations

Proper thermal management is essential for reliable operation of the LM309K:

• The TO-5 package can dissipate approximately 0.8W at 25°C free-air temperature without additional heatsinking
• For higher power applications, attach the device to an appropriate heatsink
• Thermal resistance from junction to ambient is approximately 150°C/W for the TO-5 package without heatsink
• The internal thermal shutdown activates at approximately 175°C, protecting the device from thermal damage

Design Considerations

When implementing the LM309K in your design, consider these guidelines:

Input Capacitor

While not strictly required for stability, a 0.1μF to 1μF ceramic or tantalum capacitor placed close to the input pin is recommended to improve transient response and reduce input impedance at high frequencies.

Output Capacitor

A minimum 0.1μF output capacitor improves stability and transient response. For applications with rapidly changing loads, larger values (up to 10μF) may be beneficial.

PCB Layout

• Keep input and output capacitor leads as short as possible
• Use adequate copper area for heat dissipation
• Route high-current paths with wide traces
• Separate analog and digital ground returns when used in mixed-signal systems

Reliability Data

The LM309K demonstrates excellent reliability characteristics:

• MTBF (Mean Time Between Failures): >1,000,000 hours at 25°C
• ESD Protection: 2kV Human Body Model
• Moisture Sensitivity Level (MSL): 1 (Unlimited floor life at <30°C/85% RH)

Compliance Information

• RoHS Compliant (lead-free option available)
• REACH compliant
• Manufactured in ISO 9001 certified facilities