Datasheet

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6-Channel Intelligent Fan Controller

MAX31785

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

19-5703; Rev 3; 8/12

+Denotes a lead(Pb)-free/RoHS-compliant package.

T = Tape and reel.

*EP = Exposed pad.

General Description

The MAX31785 is a closed-loop multichannel fan con-

troller. Automatic closed-loop fan control saves system

power by operating the fans at the lowest possible

speeds. Added benefits of slower fan speeds include

lower audible noise, longer fan life, and reduced system

maintenance. Based on a user-programmable lookup

table (LUT), the device automatically adjusts the speeds

of the six independent fans based on one or more of the

11 available temperature sensors. Alternately, an exter-

nal host can manually command the fan speeds and the

device automatically adjusts the fan speeds. The device

contains a fan-health-diagnostic function to help users

predict impending fan failures. The device can also

monitor up to six remote voltages.

Applications

Network Switches/Routers

Base Stations

Servers

Smart Grid Network Systems

Industrial Controls

Ordering Information

Features

S Six Independent Channels of Fan Control

Supports 3-Wire and 4-Wire Fans

Automatic Closed-Loop Fan Speed Control

RPM- or PWM-Based Control

Optional Manual Mode Control

Fast and Slow PWM Frequency Options

Staggered Fan Spin-Up Eases Power-Supply

Stress

Dual Tachometer (12-Fan Support)

Fan-Fault Detection

Fan-Health Status Meter

Nonvolatile Fan Operating Run Time Meter

S Supports Up to 11 Temperature Sensors

Up to Six External Thermal Diodes with

Automatic Series Resistance Cancellation

One Internal Temperature Sensor

Up to Four I

C Digital Temperature Sensors

Fault Detection on All Temperature Sensors

S Available 6-Channel ADC to Measure Remote

Voltages

S PMBus™-Compliant Command Interface

S I

C/SMBus-Compatible Serial Bus with Bus

Timeout Function

S On-Board Nonvolatile Fault Logging and Default

Configuration Setting

S No External Clocking Required

S +3.3V Supply Voltage

PMBus is a trademark of SMIF, Inc.

PART TEMP RANGE PIN-PACKAGE

MAX31785ETL+

-40NC to +85NC

40 TQFN-EP*

MAX31785ETL+T

-40NC to +85NC

40 TQFN-EP*

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.

Summary of content (48 pages)

PAGE 1
9-5703; Rev 3; 8/12 6-Channel Intelligent Fan Controller The MAX31785 is a closed-loop multichannel fan controller. Automatic closed-loop fan control saves system power by operating the fans at the lowest possible speeds. Added benefits of slower fan speeds include lower audible noise, longer fan life, and reduced system maintenance.
PAGE 2
MAX31785 6-Channel Intelligent Fan Controller TABLE OF CONTENTS Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Recommended Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 DC Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PAGE 3
6-Channel Intelligent Fan Controller Fan Control Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Dual Fan Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Automatic Fan Control Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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MAX31785 6-Channel Intelligent Fan Controller TABLE OF CONTENTS (continued) MFR_DATE (9Dh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 MFR_SERIAL (9Eh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 MFR_MODE (D1h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PAGE 5
6-Channel Intelligent Fan Controller Table 1. PMBus Command Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Table 2. PMBus/SMBus Serial-Port Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Table 3. PMBus Command Code Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PAGE 6
MAX31785 6-Channel Intelligent Fan Controller ABSOLUTE MAXIMUM RATINGS Operating Temperature Range........................... -40NC to +85NC Storage Temperature Range............................. -55NC to +125NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow).......................................+260NC VDD to VSS............................................................-0.3V to +5.5V RS- to VSS......................................................
PAGE 7
6-Channel Intelligent Fan Controller (VDD = 2.7V to 5.5V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at VDD = 3.3V, TA = +25NC, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS ADC Internal Reference Temperature Drift ADC Internal Reference Initial Accuracy (+25NC) ADC Full-Scale Input Voltage VFS ADC Measurement Resolution VLSB MAX UNITS -0.5 +0.5 % -1 +1 mV 1.237 V 1.213 TYP 1.
PAGE 8
MAX31785 6-Channel Intelligent Fan Controller I2C/SMBUS INTERFACE ELECTRICAL CHARACTERISTICS (VDD = 2.7V to 5.5V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at VDD = 3.3V, TA = +25NC, unless otherwise noted.) PARAMETER SYMBOL SCL Clock Frequency fSCL Bus Free Time Between STOP and START Conditions tBUF Hold Time (Repeated) START Condition CONDITIONS MIN TYP 10 (Note 5) MAX UNITS 100 kHz 1.4 ms tHD:STA 4.0 Fs Low Period of SCL tLOW 4.
PAGE 9
6-Channel Intelligent Fan Controller (TA = +25°C, unless otherwise noted.) SUPPLY CURRENT vs. TEMPERATURE (VDD = 3.3V, NO PWM SWITCHING) SUPPLY CURRENT vs. SUPPLY VOLTAGE (NO PWM SWITCHING) 3.6 3.8 3.6 3.4 3.2 3.2 IDD (mA) 3.4 3.0 3.0 2.8 2.8 2.6 2.6 2.4 2.4 2.2 2.2 2.0 2.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 -40 5.5 0V -20 0 20 40 60 80 100 VDD (V) TEMPERATURE (°C) WEAK PULLUP VOLTAGE vs. TIME DURING POWER-UP IDD vs. TIME DURING A NONVOLATILE LOG WRITE (TA = +25°C, VDD = 3.
PAGE 10
6-Channel Intelligent Fan Controller VSS REG18 TACH3 PWM2 TACH2 TACH1 PWM1 PWM0 TOP VIEW REG25 TACH0 MAX31785 Pin Configuration 30 29 28 27 26 25 24 23 22 21 SDA 31 20 PWM3 SCL 32 19 TACH4 A0 33 18 PWM4 FAULT 34 17 TACH5 CONTROL 35 16 PWM5 MAX31785 VSS 36 15 MSCL A1/TACHSEL 37 14 MSDA ALERT 38 RS-5 39 13 RST EP + 12 RS-2 11 RS+2 6 7 8 9 10 RS+1 VDD RS-1 RS+4 5 RS-0 VSS 4 RS+0 3 RS-3 2 RS+3 1 RS-4 RS+5 40 TQFN (6mm × 6mm × 0.
PAGE 11
6-Channel Intelligent Fan Controller PIN NAME FUNCTION 20 PWM3 Fan PWM Output #3. CMOS push-pull output. Low when the fan is disabled. A 100% duty cycle implies this pin is continuously high. 22 REG18 Regulator for Low-Voltage Digital Circuitry. Bypass REG18 to VSS with 1FF and 10nF capacitors. Do not connect other circuitry to this pin. 23 TACH3 Fan Tachometer Input 24 PWM2 Fan PWM Output #2. CMOS push-pull output. Low when the fan is disabled.
PAGE 12
6-Channel Intelligent Fan Controller MAX31785 Block Diagram VDD VSS REG25 VSS REG18 VSS POWER CONTROL MSCL PULSEWIDTH MODULATOR 2.5V VREG 1.8V VREG 4MHz OSCILLATOR MSDA MAX31785 SMBus MASTER INTERFACE 16-BIT MAXQ® RISC CORE FAN TACHOMETER INPUTS RST SCL ALERT CONTROL FAULT A0 A1/TACHSEL SMBus SLAVE INTERFACE SYSTEM CONTROL SIGNALS MAXQ is a registered trademark of Maxim Integrated Products, Inc.
PAGE 13
6-Channel Intelligent Fan Controller +3.3V ALERT HOST INTERFACE CLOCK DATA CONTROL RST SDA SCL RST ALERT MAX31785 #0 FAULT CONTROL A1/TACHSEL A0 +3.
PAGE 14
MAX31785 6-Channel Intelligent Fan Controller Detailed Description The MAX31785 is a closed-loop fan controller. Automatic closed-loop fan control saves system power by operating the fans at the lowest possible speeds. Added benefits of slower fan speeds include lower audible noise, longer fan life, and reduced system maintenance.
PAGE 15
6-Channel Intelligent Fan Controller CODE 9Dh 9Eh D1h D4h D6h D7h D9h DCh DDh F0h F1h F2h F3h F5h F6h F7h F8h F9h COMMAND NAME TYPE MFR_DATE Block R/W MFR_SERIAL Block R/W MFR_MODE R/W Word MFR_VOUT_PEAK R/W Word MFR_TEMPERATURE_PEAK R/W Word MFR_VOUT_MIN R/W Word MFR_FAULT_RESPONSE R/W Byte MFR_NV_FAULT_LOG Block Read MFR_TIME_COUNT Block R/W MFR_TEMP_SENSOR_CONFIG R/W Word MFR_FAN_CONFIG R/W Word MFR_FAN_LUT Block R/W MFR_READ_FAN_PWM Read Word MFR_FAN_FAULT_LIMIT R/W Word MFR_FAN_WARN_LIMIT R/W Word
PAGE 16
MAX31785 6-Channel Intelligent Fan Controller Address Select Table 2. PMBus/SMBus Serial-Port Address A1 7-BIT SLAVE ADDRESS A0 100kI to VSS 100kI to VDD On device power-up, the device samples the A0 and A1 pins to determine the PMBus/SMBus serial-port address. 100kI to VSS 1010 010 (A4h) 100kI to VDD 1010 011 (A6h) 100kI to VSS 100kI to VDD 1010 100 (A8h) SMBus/PMBus Operation The device implements the PMBus command structure using the SMBus format.
PAGE 17
6-Channel Intelligent Fan Controller continuous data stream. All the devices addressed during this transaction wait for the host to issue a STOP before beginning to respond to the command.
PAGE 18
MAX31785 6-Channel Intelligent Fan Controller Alert Response Address (ARA) Byte Format 1 7 S ARA 0001100 1 R 1 8 1 1 A DEVICE SLAVE ADDRESS WITH LSB = 0 NA P Host Sends or Reads Too Few Bits If for any reason the host does not complete writing a full byte or reading a full byte from the device before a START or STOP is received, the device does the following: 1) Ignores the command. 2) Sets the CML bit in STATUS_BYTE. 3) Sets the CML bit in STATUS_WORD.
PAGE 19
6-Channel Intelligent Fan Controller 1) ACKs the address byte. 2) Ignores the command. 3) Sends all ones (FFh) as long as the host keeps acknowledging. 4) Sets the CML bit in STATUS_BYTE. 5) Sets the CML bit in STATUS_WORD. 6) Sets the DATA_FAULT bit in STATUS_CML. 7) Notifies the host through ALERT assertion (if enabled). Host Writes to a Read-Only Command When a write request is issued to a read-only command, the device does the following: 1) Ignores the command. 2) Sets the CML bit in STATUS_BYTE.
PAGE 20
MAX31785 6-Channel Intelligent Fan Controller Table 3. PMBus Command Code Coefficients PARAMETER UNITS RESOLUTION MAX m b R Voltage VOUT_OV_FAULT_LIMIT VOUT_OV_WARN_LIMIT VOUT_UV_WARN_LIMIT VOUT_UV_FAULT_LIMIT READ_VOUT MFR_VOUT_PEAK MFR_VOUT_MIN mV 1 32,767 1 0 0 Voltage Scaling VOUT_SCALE_MONITOR — 1/32,767 1 32,767 0 0 OT_FAULT_LIMIT OT_WARN_LIMIT READ_TEMPERATURE_1 MFR_TEMPERATURE_PEAK NC 0.01 327.
PAGE 21
6-Channel Intelligent Fan Controller PARAMETER REQUIRED CONDITIONS FOR ACTIVE MONITORING ACTION DURING A FAULT Overvoltage Voltage Monitoring Enabled (ADC_ENABLE in MFR_MODE = 1) Continue Monitoring Undervoltage Voltage Monitoring Enabled (ADC_ENABLE in MFR_MODE = 1) Continue Monitoring Temp Sensor Enabled (ENABLE in MFR_TEMP_SENSOR_CONFIG = 1) Continue Monitoring Fan Enabled (Bit 7 in FAN_CONFIG_1_2 = 1) Continue Monitoring Overtemperature Fan Speed Fault Management and Reporting For reporti
PAGE 22
MAX31785 6-Channel Intelligent Fan Controller Fan Control Operation Fan control has four operational modes. The mode is determined by the combination of FAN_COMMAND_1 and bit 6 of FAN_CONFIG_1_2 (see Table 7). Fan control can be disabled by setting bit 7 in FAN_CONFIG_1_2 to zero. Dual Fan Applications In dual fan applications operating in RPM mode, the tachometer selected when TACHSEL = 0 is closeloop-controlled to the target RPM.
PAGE 23
6-Channel Intelligent Fan Controller REMOTE DIODE TEMP SENSOR 0 REMOTE DIODE TEMP SENSOR 1 TEMP SENSOR TO FAN MAPPING MAX31785 OFFSET ADJUSTMENT ALLOWS TEMPERATURE ZONE NORMALIZATION EACH FAN HAS A UNIQUE 8-LEVEL LUT TEMP SENSOR DIODE 0 +15°C FAN 2 FAN 0 1 2 3 4 5 TEMP SENSOR DIODE 1 +10°C FAN 0 1 2 3 4 5 TEMP SENSOR DIODE 2 REMOTE DIODE TEMP SENSOR 2 0°C HIGHEST TEMPERATURE CONTROLS THE FAN FAN 0 1 2 3 4 5 FAN 5 TEMP SENSOR I2C 3 I2C REMOTE TEMP SENSOR 3 0°C FAN 0 1 2 3 4 5 TEMP SENSOR
PAGE 24
MAX31785 6-Channel Intelligent Fan Controller At temperature sample 2, the temperature has increased to greater than temperature level 4 so again the PWM duty cycle must be increased. At temperature sample 3, the temperature has dropped but not below the thermal hysteresis level (which is set by the HYS bits in the MFR_FAN_CONFIG command code), so the fan speed remains at level 4. At temperature sample 4, the temperature has dropped below the hysteresis point so the PWM duty cycle is decreased.
PAGE 25
6-Channel Intelligent Fan Controller function is enabled, it runs once per second for each enabled fan. If the fan’s PWM duty cycle has been stable for 30s, the measured RPM is compared to the expected RPM and the correct fan-health-color bit (GREEN, ORANGE, or RED) is set in STATUS_FAN_1_2. If the duty cycle has been unstable for greater than 10 minutes, the YELLOW bit is set in STATUS_FANS_1_2. Fan Health-Meter Function The expected fan-speed profile is entered with the MFR_FAN_PWM2RPM command.
PAGE 26
MAX31785 6-Channel Intelligent Fan Controller fan’s PWM duty cycle is between 40% and 80%. The masured fan speed is also compared to the expected at 100% duty cycle. In the 40% to 80% range, a fan’s expected fan-speed profile is approximately linear. At duty cycles outside this range (with the exception of 100%), the shape of the expected fan-speed profile varies too much between fans, and it is not possible to predict an expected speed.
PAGE 27
6-Channel Intelligent Fan Controller A summary of the PMBus commands supported by the device are described in the following sections. PAGE (00h) The device can control up to six fans, up to 11 temperature sensors, and measure up to six remote voltages using one PMBus (I2C) address. Send the PAGE command with data 0 to 22 to select which fan, temperature sensor, or remote voltage fan is affected by all the PMBus commands shown in Table 1. Not all commands are supported within each page.
PAGE 28
MAX31785 6-Channel Intelligent Fan Controller CLEAR_FAULTS (03h) The CLEAR_FAULTS command is used to clear any fault or warning bits in the status registers that have been set. This command clears all bits simultaneously. If a fault is still present after the CLEAR_FAULTS command is executed, the fault status bit is set again and the host is also notified by asserting ALERT (if enabled in MFR_MODE). This command is write-only. There is no data byte for this command.
PAGE 29
6-Channel Intelligent Fan Controller VOUT_SCALE_MONITOR (2Ah) VOUT_SCALE_MONITOR is used in applications where the measured remote voltage is not equal to the voltage at the ADC input. For example, if the ADC input expects a 1.0V input for a 12V output, VOUT_SCALE_MONITOR = 1.0V/12V = 0.0833. In applications where the remote voltage is greater than the device input range, the voltage of the remote supply is sensed through a resistive voltage-divider.
PAGE 30
MAX31785 6-Channel Intelligent Fan Controller FAN_COMMAND_1 (3Bh) The FAN_COMMAND_1 command is used to override the device’s automatic fan-control function and force the fan to either a fixed PWM duty-cycle value or a target fan speed (in RPM). The units of FAN_COMMAND_1 are either percent duty cycle (if bit 6 of FAN_CONFIG_1_2 is zero) or RPM (if bit 6 of FAN_CONFIG_1_2 is one). Any value less than 0% duty cycle or 0 RPM causes the device to ignore this command and use the automatic fan-control function.
PAGE 31
6-Channel Intelligent Fan Controller 1) Sets the NONE OF THE ABOVE bit in STATUS_BYTE. 2) Sets the NONE OF THE ABOVE and VOUT bits in STATUS_WORD. 3) Sets the VOUT_UV_WARN bit in STATUS_VOUT. 4) Notifies the host using ALERT assertion (if enabled in MFR_MODE). VOUT_UV_FAULT_LIMIT (44h) The VOUT_UV_FAULT_LIMIT command sets the value of the output voltage that causes an output undervoltage fault. The monitored voltage must increase by at least 2% above the limit before the fault is allowed to clear.
PAGE 32
MAX31785 6-Channel Intelligent Fan Controller STATUS_BYTE (78h) The STATUS_BYTE command returns 1 byte of information with a summary of the most critical faults. A value of 1 indicates that a fault or warning event has occurred and a 0 indicates otherwise. Bits for unsupported features are reported as 0. The STATUS_BYTE cannot be restored by the RESTORE_DEFAULT_ALL command. The STATUS_BYTE message content is described in Table 16. This command is read-only. Table 16.
PAGE 33
6-Channel Intelligent Fan Controller Table 19. STATUS_CML BIT BIT NAME 7 COMM_FAULT An invalid or unsupported command has been received. 6 DATA_FAULT An invalid or unsupported data has been received. 5:1 0 0 FAULT_LOG_FULL MEANING These bits always return a 0. MFR_NV_FAULT_LOG is full and needs to be cleared. STATUS_MFR_SPECIFIC (80h) The STATUS_MFR_SPECIFIC command returns 1 byte of information with a summary of the reason for a fault.
PAGE 34
MAX31785 6-Channel Intelligent Fan Controller READ_VOUT (8Bh) The READ_VOUT command returns the actual measured output voltage. READ_VOUT is measured and updated every 10ms. The 2 data bytes are in DIRECT format. READ_TEMPERATURE_1 (8Dh) The READ_TEMPERATURE_1 command returns the temperature returned from the temperature sensor. The value of READ_TEMPERATURE_1 does not have offset from MFR_TEMP_SENSOR_CONFIG added.
PAGE 35
6-Channel Intelligent Fan Controller Table 22. MFR_MODE BIT BIT NAME MEANING FORCE_NV_FAULT_LOG Setting this bit to 1 forces the device to log data into the nonvolatile fault log. Once set, the device clears this bit when the action is completed. The host must set again for subsequent action. If an error occurs during this action, the device sets the CML bit in STATUS_BYTE and STATUS_WORD; no bits are set in STATUS_CML.
PAGE 36
MAX31785 6-Channel Intelligent Fan Controller MFR_VOUT_PEAK (D4h) The MFR_VOUT_PEAK command returns the maximum actual measured output voltage. To reset this value to 0, write to this command with a data value of 0. Any values written to this command are used as a comparison for future peak updates. The 2 data bytes are in DIRECT format. MFR_TEMPERATURE_PEAK (D6h) The MFR_TEMPERATURE_PEAK command returns the maximum measured temperature.
PAGE 37
6-Channel Intelligent Fan Controller There is a FAULT_LOG_COUNT (16-bit counter) at the beginning of each fault log that indicates which fault log is the latest. This counter rolls over should more than 65,535 faults be logged. This counter is not cleared when the CLEAR_NV_FAULT_LOG bit in MFR_MODE is toggled. The 255 bytes returned by the MFR_NV_FAULT_LOG command are described in Table 24.
PAGE 38
MAX31785 6-Channel Intelligent Fan Controller Table 24.
PAGE 39
6-Channel Intelligent Fan Controller BYTE PARAMETER BYTE MAX31785 Table 24.
PAGE 40
MAX31785 6-Channel Intelligent Fan Controller MFR_TIME_COUNT (DDh) The MFR_TIME_COUNT command returns the number of seconds of device lifetime operation. Once every hour, the device automatically stores this counter in flash memory. The counter is a 32-bit value that rolls over. The latest stored value is automatically recalled from flash memory upon device power cycle, RST action, or a soft reset.
PAGE 41
6-Channel Intelligent Fan Controller Table 26. MFR_FAN_CONFIG BIT BIT NAME MEANING The FREQ bits set the PWM frequency. Note: The device does not support pulse stretching. 15:13 12 FREQ[2:0] DUAL_TACH FREQ2 FREQ1 FREQ0 PWM FREQUENCY 0 0 0 30Hz 0 0 1 50Hz 0 1 0 100Hz 0 1 1 150Hz 1 0 0 Reserved 1 0 1 Reserved 1 1 0 Reserved 1 1 1 25kHz 0 = Dual tach functionality is disabled. 1 = Dual tach functionality is enabled.
PAGE 42
MAX31785 6-Channel Intelligent Fan Controller Table 26. MFR_FAN_CONFIG (continued) BIT BIT NAME MEANING The RAMP bits select how fast the device ramps the PWM from one duty cycle to another (either up or down). In PWM mode, the following table always applies. In RPM mode, the fan speed is read either every 200ms or 1000ms and when the reported fan speed is within 20% of the target speed, the maximum allowed PWM duty cycle change is set to 1%.
PAGE 43
6-Channel Intelligent Fan Controller USER NOTE: The programmable configuration of MFR_FAN_LUT must be monotonic. Table 27. MFR_FAN_LUT BYTE NUMBER WORD NAME 0-1 TEMP STEP 0 Temperature for step 0. MEANING 2-3 SPEED STEP 0 Fan PWM duty cycle or fan speed for step 0. 4-5 TEMP STEP 1 Temperature for step 1. 6-7 SPEED STEP 1 Fan PWM duty cycle or fan speed for step 1. 8-9 TEMP STEP 2 Temperature for step 2. 10-11 SPEED STEP 2 Fan PWM duty cycle or fan speed for step 2.
PAGE 44
MAX31785 6-Channel Intelligent Fan Controller FAN SPEED STEP: Fan PWM Duty Cycle or Fan Speed Setting If bit 6 in FAN_CONFIG_1_2 is set to zero, the FAN SPEED STEP sets the fan PWM duty cycle at each temperature step breakpoint. The valid duty cycle range is 0 to 100 (inclusive). Any values greater than 100 (decimal) result in 100% PWM duty cycle being generated, and any values less than 0 (decimal) result in 0% PWM duty cycle.
PAGE 45
6-Channel Intelligent Fan Controller MFR_FAN_FAULT_LIMIT (F5h) The MFR_FAN_FAULT_LIMIT command sets the value of the fan speed (in RPM) or percentage of target fan speed that causes a fan fault. Fans operating below these limits for over 10s continuous trip the fault. When the fan is operating in RPM mode, the 10s checking period starts after the device has completed a PWM ramp of the fan speed. The slowest tachometer signal the device can measure for a fan is 60 RPM.
PAGE 46
MAX31785 6-Channel Intelligent Fan Controller MFR_FAN_RUN_TIME (F7h) The MFR_FAN_RUN_TIME command returns the number of hours of fan lifetime operation. Once every hour, the device automatically stores this counter in flash memory. The counter is a 16-bit value that rolls over. The latest stored value is automatically recalled from flash memory upon device power cycle or RST action or a soft reset.
PAGE 47
6-Channel Intelligent Fan Controller OPTIONAL SUPPORT FOR TWO FANS UP TO 4 CHANNELS DS75LV I2C TEMP SENSOR 6 CHANNELS PWM0 TACH0 RS+0 MSDA MSCL FROM TACHSEL RS-0 +3.
PAGE 48
6-Channel Intelligent Fan Controller MAX31785 Revision History REVISION NUMBER REVISION DATE 0 12/10 Initial release 1 11/11 Updated the lead temperature in the Absolute Maximum Ratings section, VIL(MIN) and VI2C_IL(MIN) values in the Recommended Operating Conditions, INL (MAX) value in the DC Electrical Characteristics, and page numbers in Table 6 2 1/12 Added Note 4 to the INL parameter and removed the DNL parameter in the DC Electrical Characteristics 8/12 Added Note 5 to the tBUF parameter