WM8310 datasheet(284/291 Pages) WOLFSON

284 / 291 page

WM8310

Pre-Production

PP, May 2012, Rev 3.1

284

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 VNTCMON 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 VNTCMON > 0.765 x VNTCBIAS

The Hot Battery condition is detected when VNTCMON < 0.348 x VNTCBIAS

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 VNTCMON 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.

WM8310 Datasheet(PDF) 284 Page - Wolfson Microelectronics plc