Ext_temp_cal – Maxim Integrated MAX15303 PMBus Command Set User Manual
Page 34
MAX15303 PMBus Command Set User’s Guide
Page 34 of 52
EXT_TEMP_CAL
EXT_TEMP_CAL signal are as follows:
Data Byte
Number
Data Byte
Name
Units
Description
0
m
None
Combined temperature gain correction and diode ideality
factor
1
b
°K
Temperature offset correction
2
IoutTC
∆/°C
Current-sense element temperature coefficient of resistivity
Temperature Calibration
When reading or writing the EXT_TEMP_CAL command data, note that only the decimal portion of the
gain correction term (data byte 0) is sent to allow greater numerical precision within the constraints of
the PMBus Linear data format. In other words, the gain correction term is summed with 1 internally
when received by the MAX15303. Be sure to take this into account when working with the gain
correction term.
The default gain term is nominally set for use with a Fairchild MMBT3904 transistor diode junction. To
correct the gain term for a different temperature sense transistor, do the following:
1. Read the existing value of EXT_TEMP_CAL from the device
2. Sum the gain correction term value with 1.0
3. Multiply the resulting value of the gain correction term by the new transistor ideality factor
4. Divide the result by 1.004
5. Subtract 1.0 from the result
6. Send the final result back to the device
Note that the Maxim PowerTool GUI performs the addition and subtraction of 1.0 automatically.
Current-Sense Temperature Compensation
The value of IoutTC is used to provide current-sense temperature compensation. The
resistance value is multiplied by (
– 25°C) and by (IoutTC + 1) to determine the
temperature-compensated resistance, which is used in turn to calculate