WM8310 datasheet(105/291 Pages) WOLFSON

105 / 291 page

Pre-Production

WM8310

PP, May 2012, Rev 3.1

105

Note that connecting the BATTVDD pin directly to a load is not recommended; this may lead to

incorrect behaviour of the battery charger. A filter capacitor between BATTVDD and GND is

recommended to ensure best performance of the battery charger; for specific recommendations, refer

to the WM8310 evaluation board users manual.

The Wall Adaptor supply connects to SYSVDD via a FET switch as illustrated in Figure 24. The FET

switch is necessary in order to provide isolation between the Wall supply and the Battery/USB

supplies. The Wall Adapter voltage is sensed directly on the WALLVDD pin; this allows the WM8310

to determine the preferred supply, including when the Wall FET is switched off.

The gate connection to the Wall FET is driven by the WALLFETENA

¯¯¯¯¯¯¯¯¯¯¯¯ pin. The drive strength of this pin

can be selected using the WALL_FET_ENA_DRV_STR register bit as described in Section 17.3.

Note that, when the Wall Adapter is the preferred power supply, the Battery will be used if necessary

to supplement the current provided at SYSVDD.

If the Wall Adapter power source is not used, then the associated FET may be omitted, as illustrated

in Figure 24.

The main battery connects directly to the BATTVDD pin. The voltage at the battery is sensed using

the BATTVMON pin.

It is highly recommended that an external FET is connected between BATTVDD and SYSVDD as

illustrated in Figure 24. Under battery-powered operation, this FET controls the current flow from the

battery to SYSVDD. By using this external path, the power losses under heavy load conditions are

reduced, and power efficiency is increased. When this FET is not present, all the system current flows

internally from BATTVDD to SYSVDD, which can lead to unnecessary thermal losses. The external

Battery FET should always be used for average loads in excess of 1A.

The gate connection to the Battery FET is driven by the BATTFETENA

¯¯¯¯¯¯¯¯¯¯¯ pin. The functionality of this

pin is enabled by setting the BATT_FET_ENA register bit, as described in Section 17.2.

If the average load drawn from the Battery is less than 1A, then the associated FET may be omitted,

as illustrated in Figure 24. Note that the external FET is open during battery charging.

The USB interface connects directly to the USBVDD pin. The WM8310 can use this pin as an input to

power the device and/or to charge a battery connected to the BATTVDD pin. The voltage at the USB

supply is sensed using the USBVMON pin.

Note that, when USB is the preferred power supply, the Battery will be used if necessary to

supplement the current drawn from the USBVDD pin.

A backup power source can be supported using a coin cell, super/gold capacitor, or else a standard

capacitor, connected to the LDO12VOUT pin. When no other supply is available, the backup source

provides power to maintain the RTC memory whilst in the BACKUP power state. At other times, the

LDO12VOUT pin provides a constant-voltage output to maintain the backup power source. See

Section 17.6 for more details of Backup Power.

The status of the Wall and USB power supplies is indicated in the System Status register, as

described in Table 52. When PWR_WALL or PWR_USB is set, this indicates that the corresponding

power source is available for powering the WM8310.

If the status of either these power supplies changes, indicating a connection, disconnection, or a

voltage that is outside the required limits, the Power Path Source interrupt, PPM_PWR_SRC_EINT, is

set (see Section 17.5). Note that this interrupt does not indicate the availability of the battery power

source.

The PWR_SRC_BATT bit indicates when the battery is supplying current to the WM8310. This

includes when the battery is supplementing the Wall or USB power supply sources.

WM8310 Datasheet(PDF) 105 Page - Wolfson Microelectronics plc

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