JAJSH44C April 2011 – March 2019 UCD90120A
If the host system has the option of not using the temperature-sensing capability of the UCD90120A, it can still provide the desired temperature to the UCD90120A through PMBus. The host may have temperature measurements available through I2C or SPI interfaced temperature sensors. The UCD90120A would use the temperature given by the host in place of an external temperature measurement for a given rail. The temperature provided by the host would still be used for detecting overtemperature warnings or faults, logging peak temperatures, input to Boolean logic-builder functions, and feedback for the fan-control algorithms. To write a temperature associated with a rail, the PMBus command used is the READ_TEMPERATURE_2 command. If the host writes that command, the value written will be used as the temperature until another value is written. This is true whether a monitor pin was assigned to the temperature or not. When there is a monitor pin associated with the temperature, once READ_TEMPERATURE_2 is written, the monitor pin is not used again until the part is reset. When there is not a monitor pin associated with the temperature, the internal temperature sensor is used for the temperature until the READ_TEMPERATURE_2 command is written.