WM8311 datasheet(111/302 Pages) WOLFSON

111 / 302 page

Pre-Production

WM8311

PP, May 2012, Rev 3.1

111

ADDRESS

BIT

LABEL

DESCRIPTION

IM_PPM_PWR_SRC_EINT

Interrupt mask.

0 = Do not mask interrupt.

1 = Mask interrupt.

Default value is 1 (masked)

IM_PPM_USB_CURR_EIN

Interrupt mask.

0 = Do not mask interrupt.

1 = Mask interrupt.

Default value is 1 (masked)

Table 56 Power Path Management Interrupts

17.6 BACKUP POWER

As an option, a backup power source can be provided for the WM8311. This is provided using a coin

cell, super/gold capacitor, or else a standard capacitor, connected to the LDO12VOUT pin.

Note that a 22kΩ series resistor should also be connected to the backup power source.

The LDO12VOUT pin provides a constant-voltage output for charging the backup power source

whenever the SYSVDD power domain is available.

The purpose of the backup is to power the always-on functions such as the crystal oscillator, RTC and

ALARM control registers. The backup power also maintains a ‘software scratch’ memory area in the

even when the main battery is removed and no other power supply is available.

The backup duration will vary depending upon the backup power source characteristics. A typical coin

cell can provide power to the WM8310 in BACKUP mode for a month or more whilst also

maintainingthe RTC and the ‘software scratch’ register.

If a standard capacitor is used as the backup power source, then it is particularly important to

minimise the device power consumption in the BACKUP state. A 22

F capacitor will maintain the

device settings for up to 5 minutes in ‘unclocked’ mode, where power consumption is minimised by

stopping the RTC in the BACKUP state. The RTC is unclocked in the BACKUP state if the

XTAL_BKUPENA register field is set to 0, as described in Section 20.5.

17.7 BATTERY CHARGER

17.7.1 GENERAL DESCRIPTION

The WM8311 incorporates a battery charger which is designed for charging single-cell lithium

batteries. The battery charger can operate from either the Wall or USB power sources. The battery

charger implements constant-current (CC) and constant-voltage (CV) charge methods, and can run

automatically without any intervention required by the host processor.

The battery charger voltage and current are programmable. Trickle charging and fast charging modes

are supported. In both modes, the SYSVDD voltage is monitored to ensure the power supply capacity

or USB current limit is not exceeded. If the SYSVDD voltage drops to 3.9V, (eg. if the USB current

limit has been reached), then the battery charge current is automatically reduced to try and prevent

further voltage drop at SYSVDD.

Under high operating load conditions, the battery may be required to supplement the USB or Wall

Adaptor power sources. Note that this capability is supported even when battery charging is enabled;

in this case, the battery provides power to the system when required, and the charger resumes when

sufficient current capacity is available.

Typical connections for the WM8311 battery charger are illustrated in Figure 25.

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