WM8311 datasheet(112/302 Pages) WOLFSON

112 / 302 page

WM8311

Pre-Production

PP, May 2012, Rev 3.1

112

Figure 25 Typical Connections for WM8311 Battery Charger

The main battery terminal is connected to BATTVDD. The WM8311 also incorporates a battery

temperature monitoring circuit, which monitors the NTC thermistor that is typically incorporated within

a rechargeable battery pack. The NTCMON pin allows the charger to detect a hot or cold battery

condition that may be outside the battery’s usable operating conditions. Battery removal is also

detected using the NTCMON pin.

The bias resistor connected between NTCBIAS and NTCMON should be a 1% tolerance resistor with

a nominal value equal to the value of the battery’s NTC thermistor at 25

C.

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.

See Section 17.7.7 for more details of the battery temperature monitoring function.

A typical battery charge cycle is illustrated in Figure 26. This shows both the trickle charge and fast

charge processes.

The trickle charge mode is a constant current mode. The small charge current in this mode is suitable

for pre-conditioning a deeply discharged battery, or when only limited power is available for battery

charging. When the charger is enabled and the conditions for fast charging are not met, then trickle

charging is selected. (Note that fast charging is not permitted if the battery voltage is below the

defective battery threshold voltage.) Trickle charging is disabled when the charger enters the fast

charging stage, or when the charge current drops to a programmable ‘End of Charge’ threshold level

at the end of the constant voltage charge phase.

The fast charge mode is also a constant current mode, but higher charge currents are possible in this

mode. In the fast charge phase, the WM8311 drives a programmable constant current into the battery

through the BATTVDD pin. During this phase, the battery voltage rises until the battery reaches the

target voltage.

When the battery reaches the target voltage (through trickle charge and/or fast charge), the charger

enters the constant voltage charge phase, in which the WM8311 regulates BATTVDD to the target

voltage. During this phase of the charge process, the charge current decreases over time as the

battery approaches its fully charged state. Battery charging is terminated when the current falls to a

programmable ‘End of Charge’ threshold level at the end of the constant voltage charge phase.

WM8311 Datasheet(PDF) 112 Page - Wolfson Microelectronics plc