WM8310 datasheet(117/291 Pages) WOLFSON

117 / 291 page

Pre-Production

WM8310

PP, May 2012, Rev 3.1

117

17.7.7

BATTERY TEMPERATURE MONITORING

As described in Section 17.7.1, the WM8310 is designed to monitor battery temperature using a

standard NTC thermistor component which is typically incorporated within the battery pack. This

allows the battery charger to detect a hot or cold battery condition that may be outside the battery’s

usable operating conditions. (Note that the temperature monitoring circuit also detects if the NTC

circuit is not connected, in order to mask any erroneous fault indications.)

The BATT_HOT_STS and BATT_COLD_STS register bits indicate if a hot battery or cold battery

temperature condition has been detected. If a battery temperature fault condition is detected, then

charging is paused temporarily and the CHG_BATT_HOT_EINT or CHG_BATT_COLD_EINT

interrupt is set (see Section 17.7.8).

Under typical circuit configurations, the hot and cold temperature conditions are designed to be +40

C

and 0

C respectively. These temperatures can be adjusted by the use of different resistor

components, as described in the Applications Information in Section 30.6.

Battery removal is also detected using the NTC circuit. This is used to terminate battery charging if a

battery is removed during charging.

The temperature monitoring circuit can be disabled by shorting NTCMON to LDO12VOUT. This is

only recommended if there is no NTC thermistor incorporated in the battery pack or if battery

temperature monitoring is provided by other methods. Note that the short between NTCMON and

LDO12VOUT is only sensed during start-up; the temperature monitoring circuit cannot be enabled /

disabled dynamically in the ON or SLEEP power states.

The battery temperature status bits are described in Table 62.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R16458

(404Ah)

Charger Status

BATT_HOT_ST

Battery Hot status

0 = Normal

1 = Battery Hot

BATT_COLD_

STS

Battery Cold status

0 = Normal

1 = Battery Cold

Table 62 Battery Temperature Status

Battery temperature monitoring is configured as illustrated in Figure 27. The principle of operation is

that a temperature change in the battery pack causes a change in resistance of the NTC thermistor,

which results in a voltage change at the NTCMON pin.

WM8310

NTCMON

BATTVDD

GND

Battery temperature

measurement

NTCBIAS

Battery monitor

source

Single-cell

lithium battery

Main battery

connection

NTC bias resistor RBIAS (100k)

NTC thermistor RNTC (100k at 25 C)

VNTCMON =

x VNTCBIAS

RNTC

100k + RNTC

Figure 27 Battery Temperature Monitoring

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