Navigating VN31 (VIPower) Obsolescence: Specs, Pinout, and Modern Replacements

Executive Summary: What is the VN31 (VIPower)?

The VN31 (VIPower) is a monolithic high-side smart power solid-state relay designed by STMicroelectronics to drive resistive or inductive loads with one side grounded. It integrates a vertical power MOSFET with intelligent control and protection circuitry on a single chip.

• Market Position: Legacy component; currently categorized as Obsolete.

• Top Features: High current capacity (31 A), low on-resistance (30 mΩ), and 5V logic-level compatibility.

• Primary Audience: Maintenance engineers servicing legacy automotive/industrial hardware and hobbyists utilizing New Old Stock (NOS) components.

• Supply Status: Obsolete. Not recommended for new designs (NRND).

1. Technical Specifications & Performance Analysis

The VN31 belongs to ST’s proprietary VIPower (Vertical Intelligent Power) family, which was a pioneer in "smart" power switching.

1.1 Core Architecture (VIPower)

The architecture combines a standard signal-level controller with a rugged power MOSFET. This "Smart" integration allows the device to self-protect against harsh electrical environments, which is why it became a staple in automotive engine compartments and industrial PLC outputs.

1.2 Key Electrical Characteristics

For procurement and design verification, the following specs are critical: 

- Continuous Output Current: Up to 31 A at a case temperature (Tc) of 85°C. 

- Operating Voltage Range: 5.5V to 26V, making it ideal for standard 12V automotive systems. 

- On-State Resistance (RDS(on)): A maximum of 30 mΩ, which minimizes power dissipation during high-current operation. 

- Logic Compatibility: The input pin is compatible with 5V CMOS/TTL logic, allowing direct interfacing with microcontrollers like Arduino or older 5V STM32 variants.

1.3 Interfaces and Connectivity

The VN31 features a simplified interface: 

- Input: 5V logic trigger. 

- Status: An open-drain diagnostic output that signals thermal shutdown or short-circuit conditions. 

- Inductive Load Handling: Includes internal clamping to manage fast demagnetization of inductive loads (like solenoids or motors).

2. Pinout, Package, and Configuration

The VN31 was primarily distributed in power-centric packages designed for heat dissipation.

2.1 Pin Configuration Guide

1. VCC: Main power supply input.

2. Input: Logic signal to turn the switch ON/OFF.

3. Status: Diagnostic feedback (Active Low during faults).

4. Output: Connected to the load.

5. GND: Logic ground reference.

2.2 Naming Convention & Ordering Codes

While the base part is the VN31, you may encounter suffixes: 

- VN31: Standard PENTAWATT (Vertical) package. 

- VN31SP: PowerSO-10 surface mount package. 

- VN31-E: Lead-free (RoHS compliant) versions produced toward the end of its lifecycle.

2.3 Available Packages

3. Design & Integration Guide (For Engineers & Makers)

Pro Tip: Because the VN31 is obsolete, do not use it for new commercial products. For repairs, ensure the heatsink contact is cleaned and reapplied with fresh thermal paste.

3.1 Hardware Implementation

• Bypass Capacitors: Place a 0.1µF ceramic capacitor close to the VCC and GND pins to filter high-frequency noise.

• Thermal Management: Driving 31A will generate significant heat despite the low RDS(on). A PENTAWATT package must be bolted to a substantial aluminum heatsink or a copper pour on the PCB.

• PCB Layout: Use wide traces (at least 100 mils per 10A) for the VCC and Output paths to prevent board delamination.

3.2 Common Design Challenges

• Issue: The device is hard to find.

• Fix: Source from reputable distributors specializing in legacy components or initiate a redesign using the alternatives listed in Section 5.

• Issue: Overheating at high currents.

• Fix: If the VN31 hits its thermal shutdown (typically 150°C), the Status pin will pull low. Improve airflow or increase the heatsink surface area.

• Issue: High Voltage Spikes from Motors.

• Fix: The VN31 has an internal -18V clamp. If driving very large inductive loads, add an external Schottky freewheeling diode across the load.

4. Typical Applications & Use Cases

4.1 Real-World Example: Automotive Power Distribution

In older vehicle models, the VN31 was used to control headlamps and seat heaters. Because it is a "high-side" switch, it sits between the battery and the load. If a wire to the lamp shorts to the chassis (ground), the VN31 detects the overcurrent and shuts down instantly, preventing a fire.

5. Alternatives and Cross-Reference Guide

Since the VN31 is obsolete, finding a replacement is the most common task for engineers today.

• Direct Replacements (STMicroelectronics): Look for the VIPower M0-7 or M0-9 series. While not usually pin-compatible, they offer much higher efficiency and smaller footprints.

• Pin-Compatible / Functional Equivalents:

• Infineon PROFET BTS Series: Specifically the BTS500xx series for high-current applications.

• NXP MC3398x Series: Rugged high-side switches designed for similar automotive environments.

• Modern Upgrade: The VN7016AJ from ST is a modern equivalent with lower RDS(on) and enhanced digital diagnostics via MultiSense technology.

6. Frequently Asked Questions (FAQ)

• Q: What is the difference between VN31 and a standard Relay?

• A: Unlike a mechanical relay, the VN31 has no moving parts (solid-state), switches much faster, and includes built-in short-circuit protection.

• Q: Can VN31 be used in 24V systems?

• A: It is rated up to 26V, which is the upper limit of a 12V system. For 24V industrial or truck systems, a 45V-rated driver is recommended.

• Q: Where can I find the VN31 datasheet?

• A: STMicroelectronics archives legacy datasheets, but they are also available on major distributor sites like Mouser or Digi-Key under "Obsolete Products."

• Q: Is VN31 suitable for PWM control?

• A: Yes, it can handle PWM for dimming lights or speed-controlling DC motors, typically up to a few kHz.

7. Resources

• STMicroelectronics VIPower Selector Guide

• Thermal Design Application Note (AN615)

• Legacy Component Sourcing Portals