MAX31785 19-5703 Rev 3 8/12 6-Channel Intelligent Fan Controller General Description Features The MAX31785 is a closed-loop multichannel fan con- S Six Independent Channels of Fan Control troller. Automatic closed-loop fan control saves system Supports 3-Wire and 4-Wire Fans power by operating the fans at the lowest possible Automatic Closed-Loop Fan Speed Control speeds. Added benefits of slower fan speeds include RPM- or PWM-Based Control lower audible noise, longer fan life, and reduced system Optional Manual Mode Control maintenance. Based on a user-programmable lookup Fast and Slow PWM Frequency Options table (LUT), the device automatically adjusts the speeds Staggered Fan Spin-Up Eases Power-Supply of the six independent fans based on one or more of the Stress 11 available temperature sensors. Alternately, an exter- Dual Tachometer (12-Fan Support) nal host can manually command the fan speeds and the Fan-Fault Detection device automatically adjusts the fan speeds. The device Fan-Health Status Meter contains a fan-health-diagnostic function to help users Nonvolatile Fan Operating Run Time Meter predict impending fan failures. The device can also S Supports Up to 11 Temperature Sensors monitor up to six remote voltages. Up to Six External Thermal Diodes with Automatic Series Resistance Cancellation Applications One Internal Temperature Sensor 2 Network Switches/Routers Up to Four I C Digital Temperature Sensors Fault Detection on All Temperature Sensors Base Stations S Available 6-Channel ADC to Measure Remote Servers Voltages Smart Grid Network Systems S PMBus-Compliant Command Interface Industrial Controls 2 S I C/SMBus-Compatible Serial Bus with Bus Timeout Function Ordering Information S On-Board Nonvolatile Fault Logging and Default PART TEMP RANGE PIN-PACKAGE Configuration Setting MAX31785ETL+ -40NC to +85NC 40 TQFN-EP* S No External Clocking Required MAX31785ETL+T -40NC to +85NC 40 TQFN-EP* S +3.3V Supply Voltage +Denotes a lead(Pb)-free/RoHS-compliant package. T = Tape and reel. *EP = Exposed pad. PMBus is a trademark of SMIF, Inc. Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device may be simultaneously available through various sales channels. For information about device errata, go to: www.maxim-ic.com/errata. For pricing, delivery, and ordering information, please contact Maxim Direct 1 at 1-888-629-4642, or visit Maxims website at www.maxim-ic.com.6-Channel Intelligent Fan Controller TABLE OF CONTENTS Absolute Maximum Ratings ................ 6 Recommended Operating Conditions ................ 6 DC Electrical Characteristics ................. 6 2 I C/SMBus Interface Electrical Characteristics ............. 8 2 I C/SMBus Timing ................... 8 Typical Operating Characteristics ............... 9 Pin Configuration ................... 10 Pin Description ................... 10 Block Diagram ................... 12 Multiple Device Connection Diagram................ 13 Detailed Description................... 14 Address Select ............................................................................. 16 SMBus/PMBus Operation ..................................................................... 16 SMBus/PMBus Communication Examples ..................................................... 16 Group Command ........................................................................... 17 Group Command Write Format .............................................................. 17 Addressing ................................................................................ 17 ALERT and Alert Response Address (ARA)....................................................... 17 Alert Response Address (ARA) Byte Format.................................................... 18 Host Sends or Reads Too Few Bits ............................................................. 18 Host Sends or Reads Too Few Bytes ............................................................ 18 Host Sends Too Many Bytes or Bits . 18 Host Reads Too Many Bytes or Bits ............................................................. 18 Host Sends Improperly Set Read Bit in the Slave Address Byte ....................................... 18 Unsupported Command Code Received ......................................................... 18 Invalid Data Received ........................................................................ 18 Host Reads from a Write-Only Command ........................................................ 19 Host Writes to a Read-Only Command........................................................... 19 SMBus Timeout............................................................................. 19 PMBus Operation ........................................................................... 19 PMBus Protocol Support...................................................................... 19 Data Format................................................................................ 19 Interpreting Received DIRECT Format Values .....................................................20 Sending a DIRECT Format Value ...............................................................20 Fault Management and Reporting .............................................................. 21 System Watchdog Timer ...................................................................... 21 Temperature Sensor Operation ................................................................. 21 2 MAX31785