What is the maximum input voltage that can be monitored by the MAX31785?

The MAX31785 has an ADC full-scale input voltage (VFS) value of 1.225V. Voltages greater than this value will continue to result in a full-scale voltage value. It is recommended to use a voltage divider circuit to keep the maximum measured voltage under 1.225V.

How can I use the TACHx input to know if the FAN works correctly in the MAX31785?

TACHx receives signals from a fan, And this value can be read from related register. The READ_FAN_SPEED_1 command returns the fan speed in RPM", so if the speed is out of the desired range you know that the fan is not working properly.

Is there an example that shows how to use SMBus/PMBus of the MAX31785? Can you describe how to use the Page command?

Page 0-22 (decimal) is used to select individual fan, temperature sensor, or remote voltage connected to the ADC. For control associated with each page, refer to Table 9 in the datasheet (Rev 3 8/12). Once selected, all control commands are for that page only. To select a page, send slave address, followed by page command, and then the data (page number). For example, by sending Start condition--Slave address--Page command (0x00) --data (0x00), Page 0 is selected. Page 0 is associated with fan connnected to PWM 0. You can then use commands to configure the fan. For commands available for Page 0, refer to Table 1 of the datasheet. For example, 0x3A (FAN_CONFIG_1_2) command can configure the fan. If you wish to control other fans, use the Page command to select the fan, then use the control commands to configure it.

MAX31785 scratchpad register or memory for storing revision

Question: Is there any scratchpad register or memory location for storing user information such as revision ID? Answer: There are no general use/user memory locations in the MAX31785. However, if you are not using the Fault and Warning limts, then you can certainly fill those registers with whatever data you like, and it will be stored to Flash when you execute the Store Default All command.

Is there a way to force the maximum fan speed on the MAX31785 using a pin?

Configuring the FAULT pin as an input pin via the MFR_FAULT_RESPONSE(register 0xD9) Bit0 = '1' will force the fan output to 100% duty cycle when the pin is externally asserted. Bit 0 of the MFR_FAULT_RESPONSE register must be set to a value of 1 for every page (channel) that the 100% duty cycle behavior is desired when the /FAULT pin is drive low. Since FAULT is an active-low, open drain input/output, the way to force the 100% duty cycle would be to tie FAULT to VDD via R_pullup and then pull it to ground to assert.

Is it possible to read all temperature sensors connected to the MAX31785 using I2C?

The MAX31785 has four configurable I2C temperature sensors and 6 internal thermal diodes. Either one can be used to control fan speed or to monitor temperature or report any faults. Using the MAX31785AEVKIT software the data can be read and can be configured to control Fan or monitor temperature. By removing the DS3900 on the EVKIT and by connecting I2C communication pins to the MAX31785EVKIT the temperature sensor's data can be monitored using the GUI.

Is there a way to force the maximum fan speed on the MAX31785 using a pin?

Configuring the FAULT pin as an input pin via the MFR_FAULT_RESPONSE(register 0xD9) Bit0 = '1' will force the fan output to 100% duty cycle when the pin is externally asserted. Bit 0 of the MFR_FAULT_RESPONSE register must be set to a value of 1 for every page (channel) that the 100% duty cycle behavior is desired when the /FAULT pin is drive low. Since FAULT is an active-low, open drain input/output, the way to force the 100% duty cycle would be to tie FAULT to VDD via R_pullup and then pull it to ground to assert.