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

6.1.5 Sequential Fan Start

When multiple high-current fans are powered on simultaneously, the startup current surge can stress the system power supply. The FAN31790 provides sequential fan activation to minimize this inrush current by inserting programmable delays between fan activations. The fans are started one at a time. The Sequential Start Delay bits (7:5 in the Failed Fan Options/Sequential Start register 14h) select the delay interval: 0s, 250ms, 500ms, 1s, 2s, or 4s between fan starts.

Sequential activation applies when fans are forced to full speed during POR, when responding to a fan failure, or when the FULL_SPEED input is asserted. Each PWM is started and will follow it's spin-up and rate-of-change settings. After the delay interval, the next PWM will start.

Note:

Delay Interval will apply even to unused or disabled PWM channels.