WM8311 Datasheet, PDF (119/302 Pages) Wolfson Microelectronics plc – Processor Power Management Subsystem

Pre-Production
WM8311
17.7.7 BATTERY TEMPERATURE MONITORING
As described in Section 17.7.1, the WM8311 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
R16458
(404Ah)
Charger Status
BIT
11
10
LABEL
BATT_HOT_ST
S
BATT_COLD_
STS
Table 62 Battery Temperature Status
DEFAULT
0
0
DESCRIPTION
Battery Hot status
0 = Normal
1 = Battery Hot
Battery Cold status
0 = Normal
1 = Battery Cold
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.
Figure 27 Battery Temperature Monitoring
w
PP, May 2012, Rev 3.1
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