WM8311 datasheet(296/302 Pages) WOLFSON

296 / 302 page

WM8311

Pre-Production

PP, May 2012, Rev 3.1

296

To select a specific Hot Battery threshold, the required NTC bias resistor value may be calculated

using the following equation:

RBIAS = (rHOT / 0.534) x R25

rHOT is the NTC thermistor resistance ratio at the desired temperature threshold

R25 is the NTC thermistor resistance at 25C

For example, at 60

C the Vishay Curve 1 resistance ratio, rHOT, is 0.2488.

Therefore, to implement a 60

C Hot Battery threshold, assuming a 100k NTC thermistor (at 25C),

the required NTC bias resistor is 46.6k

 (nearest E12 value 47k).

The resultant Cold Battery threshold is given using the rCOLD equation below. The rCOLD value needs to

be referenced to the Vishay Curve 1 resistance chart in order to find the corresponding temperature.

To select a specific Cold Battery threshold, the required NTC bias resistor value may be calculated

using the following equation:

RBIAS = (rCOLD / 3.255) x R25

rCOLD is the NTC thermistor resistance ratio at the desired temperature threshold

R25 is the NTC thermistor resistance at 25C

For example, at 5

C the Vishay Curve 1 resistance ratio, rCOLD, is 2.540.

Therefore, to implement a 5

C Cold Battery threshold, assuming a 100k NTC thermistor (at 25C),

the required NTC bias resistor is 78k

 (nearest E12 value 82k).

The resultant Hot Battery threshold is given using the rHOT equation below. The rHOT value needs to be

referenced to the Vishay Curve 1 resistance chart in order to find the corresponding temperature.

To select both the Hot Battery threshold and the Cold Battery threshold, an additional resistor, R1, is

required, as illustrated in Figure 45.

Figure 45 Battery Temperature Threshold Selection

WM8311 Datasheet(PDF) 296 Page - Wolfson Microelectronics plc