SLVSIZ2 April   2026 FAN31790

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Power Supply
    6. 5.6 Fan Controller Characteristics
    7. 5.7 External Crystal Parameters
    8. 5.8 Digital IO
      1. 5.8.1 Electrical Characteristics
      2. 5.8.2 Switching Characteristics
    9. 5.9 I2C Characteristics
      1. 5.9.1 I2C Filter
      2. 5.9.2 I2C Timing Diagram
  7. 6 Detailed Description
    1. 6.1 Fan Control
      1. 6.1.1 PWM Mode
      2. 6.1.2 RPM Mode
      3. 6.1.3 Rate-of-Change Control
      4. 6.1.4 Spin-Up
      5. 6.1.5 Sequential Fan Start
      6. 6.1.6 FULL_SPEED Input
      7. 6.1.7 I2C Watchdog Timer
      8. 6.1.8 Power-on Reset Configuration Pins
    2. 6.2 Fan Monitoring
      1. 6.2.1 Tachometer Signals
      2. 6.2.2 PWM Outputs as Tachometer Inputs
    3. 6.3 Fan Faults and Failures
      1. 6.3.1 PWM Mode Failure Detection
      2. 6.3.2 RPM Mode Failure Detection
      3. 6.3.3 Locked Rotor Mode Failure Detection
      4. 6.3.4 Failure Indication
    4. 6.4 I2C Interface
      1. 6.4.1 I2C Addresses and ADDRx Pins
      2. 6.4.2 I2C Command Structure
  8. 7 Register Map
  9. 8 Register Descriptions
    1. 8.1 Global Configuration Registers
    2. 8.2 Fan Fault Registers
    3. 8.3 TACH and PWM Status Registers
    4. 8.4 PWM Duty Cycle Control Registers
    5. 8.5 TACH Target Count Registers
    6. 8.6 Window Registers
  10. 9 Application and Implementation
    1. 9.1 Typical Application
      1. 9.1.1 Schematic
      2. 9.1.2 Configuration Examples
  11. 10Device and Documentation Support
    1. 10.1 Receiving Notification of Documentation Updates
    2. 10.2 Support Resources
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Tape and Reel Information

6 Detailed Description

The FAN31790 is a PWM fan controller IC that manages the speed and health of up to 12 independent cooling fans in a system. It communicates with a host via an I2C, allowing software to dynamically adjust fan speeds based on temperature, load, or other system conditions.

The core function of the FAN31790 is generating independent PWM signals to provide speed control for up to 6 fans. It supports two control modes: PWM mode where the duty cycle is directly specified (0-100%), and RPM mode where the device actively monitors fan tachometer feedback and automatically adjusts the PWM duty cycle to maintain a target RPM. This closed-loop control ensures fans spin at the desired speed regardless of load variations.

Beyond speed control, the FAN31790 provides comprehensive fan monitoring and diagnostics. It can read up to 12 tachometer signals (six dedicated inputs plus six configurable from the PWM outputs), allowing it to detect fan failure conditions and report faults to the host system. Additional features include acoustic optimization through controlled duty cycle rate-of-change, fan spin-up assistance for reliable starting, sequential activation of multiple fans to reduce inrush current, and an I2C watchdog timer that forces fans to full speed if the host system becomes unresponsive.