The DAC38RF82 (or DAC38RF89) incorporates a temperature sensor block which monitors the die temperature by measuring the voltage across 2 transistors. The voltage is converted to an 8-bit digital word using a successive approximation (SAR) analog to digital conversion process. The result is scaled, limited and formatted as a twos complement value representing the temperature in degrees Celsius.
The sampling is controlled by the serial interface signals SDEN and SCLK. If the temperature sensor is enabled by writing a 0 to field TSENSE_SLEEP in register SLEEP_CONFIG (8.5.70), a conversion takes place each time the serial port is written or read. The data is only read and sent out by the digital block when the temperature sensor is read in field TEMPDATA in register TEMP_PLLVOLT (8.5.7). The conversion uses the first eight clocks of the serial clock as the capture and conversion clock, the data is valid on the falling eighth SCLK. The data is then clocked out of the chip on the rising edge of the ninth SCLK. No other clocks to the chip are necessary for the temperature sensor operation. As a result the temperature sensor is enabled even when the device is in sleep mode.
In order for the process described above to operate properly, the serial port read from register TEMP_PLLVOLT must be done with an SCLK period of at least 1 μs. If this is not satisfied the temperature sensor accuracy is greatly reduced.