WM8311 datasheet(113/302 Pages) WOLFSON

113 / 302 page

Pre-Production

WM8311

PP, May 2012, Rev 3.1

113

Note that, at any time during trickle charging or fast charging, the battery may be required to

supplement the USB or Wall Adaptor power source. In this case, the battery voltage may drop while it

is providing power to the system. The charger resumes operation automatically as soon as sufficient

current capacity is available from the main power source.

After the battery has been fully charged and the charge process has been terminated, battery

charging will automatically re-start if the battery voltage falls below the charger re-start threshold.

Figure 26 A Typical Charge Cycle

17.7.2 BATTERY CHARGER ENABLE

The battery charger may be enabled when the WM8311 is in the ON or SLEEP power states. Note

that battery charging is only possible when the selected power source is within normal operating

limits. See Section 17.7.8 for further details of battery charging in the SLEEP power state.

The battery charger is enabled when the CHG_ENA register bit is set to 1. When enabled, it checks if

the conditions for charging are fulfilled and it controls the charging processes accordingly. The status

of the battery charger can be read from the CHG_ACTIVE register bit.

The target voltage for the battery is set by the CHG_VSEL field, as defined in Table 57. It is important

that this field is correctly set according to the type of battery that is connected. Incorrect setting of this

The trickle charge current is selected using the CHG_TRKL_ILIM field. This is the maximum trickle

charge current - the actual charge current will be reduced if the battery is fully charged, or if the

system supply, SYSVDD, drops as described in Section 17.7.1.

When the battery reaches the target voltage, the charger enters the constant voltage charge phase, in

which the WM8311 regulates BATTVDD to the target voltage. When the charger is in the constant

voltage charge phase, then the CHG_TOPOFF bit will be set to indicate that the charge is

approaching completion.

The WM8311 incorporates thermal sensors to detect excessive temperatures within the device and to

provide self-protection (see Section 26). By default, the battery charger will be disabled if the Thermal

Warning condition occurs, and will be re-enabled after the condition has cleared. This response can

be disabled by setting CHG_CHIP_TEMP_MON = 0, allowing the battery charge to continue. The

Thermal Warning threshold is the lower of the two device temperature thresholds; the Thermal

Shutdown threshold is the higher threshold. Note that the Thermal Shutdown condition cannot be

ignored; this event causes a System Reset and a termination of battery charging.

If the WM8311 is commanded to the OFF state for any reason, then battery charging will be

terminated. The CHG_OFF_MASK bit can be used to prevent certain OFF transitions whilst the

battery charger is active. Setting the CHG_OFF_MASK bit causes a ‘Software OFF request’, ‘ON pin

request’ or GPIO OFF request to be ignored whilst the charger is active. See Section 11.3 for a full list

of OFF transition events.

The register control fields for trickle charging are described in Table 57. See Section 17.7.4 for details

of battery charge termination.

WM8311 Datasheet(PDF) 113 Page - Wolfson Microelectronics plc