The TMP43x allow for a different η-factor value to be used for converting remote channel measurements to temperature. The remote channel uses sequential current excitation to extract a differential VBE voltage measurement to determine the temperature of the remote transistor. Equation 1 relates this voltage and temperature.
The value η in Equation 1 is a characteristic of the particular transistor used for the remote channel. When the beta compensation configuration is set to 0111 (beta compensation disabled) or the sensor is diode-connected (base shorted to collector), the η-factor used by the TMP43x is 1.008. When the beta compensation configuration is set to 1000 (beta compensation enabled) and the sensor is GND collector-connected (PNP collector to ground), the η-factor used by the TMP43x is 1. If the η-factor used for the temperature conversion does not match the characteristic of the sensor, then temperature offset is observed. The value in the η-Factor Correction Register can be used to adjust the effective η-factor according to Equation 2 and Equation 3 for disabled beta compensation or a diode-connected sensor. Equation 4 and Equation 5 can be used for enabled beta compensation and a GND collector-connected sensor.
The η-correction value must be stored in twos-complement format, yielding an effective data range from –128 to 127. Table 11 shows the η-factor range for both 1.008 and 1. For the TMP431, the η-correction value can be written to and read from pointer address 18h. For the TMP432, the η-correction value can be written to and read from pointer address 27h. The η-correction value for the second remote channel is read to and written from pointer address 28h. The register power-on reset value is 00h, thus having no effect unless written to.
|NADJUST||η = 1.008||η = 1.000|