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

4 Pin Configuration and Functions

FAN31790 28-pin ZFP (LGA) Package Figure 4-1 28-pin ZFP (LGA) Package. 28-pin ZFP (LGA) Package
Table 4-1 Pin Function
PINI/ODESCRIPTION
No.NAME
1

FREQ_START

IThis input is sampled at power-up and sets the power-up value for the PWM output frequency.
2SPIN_STARTIThis input is sampled at power-up and sets the initial spin-up behavior.
3

ADD1

I

I2C Address select inputs. Can be connected to VCC, GND, SCL, or SDA for 16 possible addresses. Address inputs sampled at the start of every I2C transmission.

4

ADD0

I
5WD_STARTI

Input sampled at power up and sets initial Watchdog Behavior.

6XTAL2IPins to connect optional 32.768kHz Crystal oscillator. A crystal can be used when additional timing precision is required. The device also has an integrated 32.768kHz internal oscillator that can be used and will be defaulted to until the crystal stabilizes.
7

XTAL1

I
8GND--

Ground

9

TACH6

I

Inputs for tachometer signals. Can be configured for digital or analog signals. If fan has digital tachometer output, these pins can be used for RPM control. In 2-pin fans, analog signal can be used to detect fan failure.

11

TACH5

I
13

TACH4

I

15

TACH3

I

17

TACH2

I
19

TACH1

I
10

PWMOUT6 (TACH12)

I/O

Open-drain output for 4-wire fan PWM inputs or for 2-pin and 3-pin fans, modulating the power transistor. Can also be configured to act as additional tachometer inputs. Can be pulled high to 3.3V.

12

PWMOUT5 (TACH11)

I/O

14

PWMOUT4 (TACH10)I/O

16

PWMOUT3 (TACH9)I/O

18

PWMOUT2 (TACH8)I/O

20

PWMOUT1

(TACH7)

I/O

21

VCC

I

Power Supply. 1.62-3.6V. Need a minimum of a .1 uF bypass cap to GND.

22

SDA

I/O

I2C Serial Data Line. Open Drain.

23

SCL

II2C Serial Clock Line. Open Drain.

24

FAN_FAIL

O

Active-low open drain fan-failure Output. Goes low when fault condition is met.

25

PWM_START0

I

Input sampled at power-up. Sets the default value for all PWMOUT duty cycles.

26

PWM_START1

I

27

FULL_SPEED

I

When driven low, this input forces all PWMs to 100% duty cycle. Only exception is if a fan has failed and "Duty cycle = 0 on failure" mode has been selected.

28

CLKOUT

O

32.768kHz Clock Output. Clock is sourced from either the external crystal or the internal oscillator when the crystal is not used. Clock output is always active.

--

Thermal Pad

--

Connect to GND.