WM8310 Datasheet, PDF (284/291 Pages) Wolfson Microelectronics plc – Processor Power Management Subsystem

WM8310
Pre-Production
30.6 BATTERY TEMPERATURE MONITORING COMPONENTS
Battery temperature monitoring is performed using a reference voltage output on the NTCBIAS pin. A
potential divider is formed between the NTC bias resistor and the NTC thermistor component within
the battery pack. The voltage present at the NTCMON pin is used to determine the battery
temperature. The recommended connections and the derivation of V_NTCMON is shown in Figure 37.
Figure 37 Battery Temperature Monitoring
The voltage thresholds for the Hot/Cold Battery Temperature conditions are fixed in the WM8310:
The Cold Battery condition is detected when V_NTCMON > 0.765 x V_NTCBIAS
The Hot Battery condition is detected when V_NTCMON < 0.348 x V_NTCBIAS
If the NTC thermistor has a nominal resistance of 100k at 25C, and follows the Vishay Resistance-
Temperature Curve 1, then the above equations result in the Hot Battery threshold = 40C and the
Cold Battery threshold = 0C.
For example, if the NTC thermistor resistance is 53.4k at 40C, then V_NTCMON is given by the
following equation:
The upper and lower temperature thresholds can be adjusted by modification of the NTC bias resistor
and/or the addition of another resistor between the battery pack and the NTCMON pin.
If only the NTC bias resistor is adjusted, then either the upper or lower threshold can be selected, but
not both; the other threshold will be determined by the thermistor characteristics.
If an additional resistor is inserted between the battery pack and the NTCMON pin, then the upper
and lower thresholds can be independently selected, with the constraint that the upper and lower
thresholds must be at least 40C apart.
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PP, May 2012, Rev 3.1
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