WM8321 datasheet(29/253 Pages) WOLFSON

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WM8321

PD, February 2012, Rev 4.0

11 DEVICE DESCRIPTION

11.1 GENERAL DESCRIPTION

The WM8321 is a multi-purpose Power Management device with a comprehensive range of features.

The WM8321 provides 4 DC-DC synchronous buck converters and 11 LDO regulators which are all

programmable to application-specific requirements. The on-board oscillator and two additional LDOs

support the clocking and control functions for the DC-DC converters and other core functions.

The WM8321 provides a 32.768kHz crystal oscillator and secure Real Time Clock (SRTC). An

auxiliary ADC is included, for measurement of external voltages. Other features include flexible GPIO

capability, and LED outputs for system status indications.

Under typical operating conditions, the device is powered up and shut down under the control of the

¯¯ pin. The device executes a programmable sequence of enabling or disabling the DC-DC

converters, LDOs and other functions when commanded to power up or shut down respectively. An

alternate device state (SLEEP power state) is provided, in which selected functions may be

separately configured for a low-power or other operating condition. The configuration of the normal

operating state may be programmed into an integrated OTP non-volatile memory. If desired, the OTP

memory can be programmed during device manufacture in accordance with the user’s specification.

See Section 14 for details of the OTP and associated bootstrap configuration functions.

In the absence of a main power supply, the WM8321 automatically reverts to a backup state, under

which a minimal functionality is maintained to enable a smooth return to normal operation when the

supply is restored. With a backup battery present, the RTC is updated in the backup state, allowing

the main battery to be depleted or changed without loss of RTC function. Without a backup battery, a

small capacitor is sufficient to maintain the RTC (unclocked) for up to 5 minutes.

11.2 POWER STATES

The WM8321 has 6 main power states, which are described below. Different levels of functionality are

associated with each of the power states. Some of the state transitions are made autonomously by

the WM8321 (eg. transitions to/from BACKUP are scheduled according to the available power supply

conditions). Other transitions are initiated as a result of instructions issued over the Control Interface

or as a result of software functions (eg. Watchdog timer) or hardware functions such as the ON

¯¯ pin.

The valid transitions and the associated conditions are detailed below.

NO POWER

- This is the device state when no power is available. All functions are disabled and all

OFF

- This is the device state when power is available but the device is switched off. The RTC is

enabled and the register map contents are maintained. The RESET

¯¯¯¯¯¯ pin is pulled low in this state.

LDO11 may optionally be enabled in this state; all other DC-DCs and LDOs are disabled (apart from

LDO12, which supports internal functions).

- This is the normal operating state when the device is switched on. All device functions are

available in this state.

SLEEP

- This is a user-configurable operating state which is intended for a low-power operating

condition. Selected functions may be enabled, disabled or re-configured according to the user’s

requirements. A programmable configuration sequence for the DC-DCs and LDOs is executed on

transition to/from SLEEP mode.

BACKUP

- This is the operating state when the PVDD power supply is below the reset threshold of

the device. Typically, this means that the PVDD supply has been removed. All DC-DC converters and

LDO regulators are disabled in this state. The RTC and oscillator and a ‘software scratch’ memory

area can be maintained from the backup supply (if available) in this state. All other functions and

registers are reset in BACKUP. (Note that, for power saving, an ‘unclocked’ mode, in which the RTC

is held constant, may be selected if required.)

PROGRAM

- This is a special operating state which is used for programming the integrated OTP

memory with the device configuration data. The settings stored in the OTP define the device

configuration in the ON state, and also the time/sequencing data associated with ON/OFF power

state transitions. See Section 14 for details of the OTP features.

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