WM8321 datasheet(66/253 Pages) WOLFSON

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WM8321

Production Data

PD, February 2012, Rev 4.0

To ensure stable operation, the register fields DCm_CAP must be set for each of the DC-DC

Converters according to the output capacitance. (Note that these fields are set via OTP/ICE settings

only; they cannot be changed by writing to the control register.) The choice of output capacitor is

described in Section 30.3.

When a DC-DC Converter is disabled, the output pin can be configured to be floating or to be actively

discharged. This is selected using DCm_FLT.

DC-DC Converters 1 and 2 also support selectable switching frequency. This can either be 2MHz or

4MHz, according to the DCm_FREQ register field. (Note that these fields are set via OTP/ICE

settings only; they cannot be changed by writing to the control register.) The switching frequency of

DC-DC3 is fixed at 2MHz.

Note that the supported output voltage range for DC-DC Converters 1 and 2 is restricted in the 4MHz

mode; for output voltages greater than 1.4V, the 2MHz mode must be used.

The switching phase of each DC-DC converter can be set using the DCm_PHASE bits. Where two

converters are operating at the same switching frequency, the supply current ripple can be minimised

by selecting a different switching phase for each converter.

The Dynamic Voltage Scaling (DVS) feature on DC-DC1 and DC-DC2 enables hardware or software

selection of an alternate output voltage, DCm_DVS_VSEL. This may be useful if a short-term

variation in output voltage is required.

The DVS voltage (set by DCm_DVS_VSEL) may be selected by setting DCm_DVS_SRC = 01.

Alternatively, the DVS voltage may be selected under control of one of the Hardware DVS Control

inputs supported via the GPIO pins. See Section 21 for details of configuring the GPIO pins as

Hardware DVS Control inputs.

Whenever the DVS voltage is selected by any method, the DVS selection takes precedence over the

ON, SLEEP or Hardware Control (HWC) configuration. See Section 15.8 for details of Hardware

Control options.

The output voltage ramp rate is selectable for DC-DC Converters 1 and 2. The DCm_RATE field

selects the rate of change of output voltage, whether this is in response to an operating mode

transition, or any hardware or software command. Note that the DCm_RATE field is accurate in

Forced Continuous Conduction Mode (FCCM); in other modes, the actual slew rate may be longer in

the case of a decreasing output voltage selection, especially under light load conditions.

The WM8321 can indicate the status of the Dynamic Voltage Scaling via a GPIO pin configured as a

“DC-DC1 DVS Done” or “DC-DC2 DVS Done” output (see Section 21). When a GPIO pin is

configured to indicate the DVS status, this signal is temporarily de-asserted during a DVS transition

on the associated DC-DC Converter, and is subsequently asserted to indicate the transition has

completed.

Note that the GPIO DVS outputs indicate the progress of all output voltage slews; they are not limited

to transitions associated with DCm_DVS_SRC; the GPIO DVS output also indicates the status of a

slew caused by a write to the DCm_ON_VSEL register, or a slew to the DCm_SLP_VSEL voltage.

Note also that the GPIO DVS outputs are indicators of the DVS control mechanism only; they do not

confirm the output voltage accuracy. The output voltage can be checked using the voltage status bits

if required (see Section 15.2).

15.6.1 DC-DC3 / DC-DC4 DUAL MODE

DC-DC Converters 3 and 4 can be configured to operate in ‘Dual’ mode, where the two converters are

ganged together to support an increased current capability. In this mode, the two converters employ a

common voltage feedback circuit in order to ensure the two outputs are accurately aligned.The dual

mode is selected by configuring DC-DC4 as a ‘Slave’ to DC-DC3.

When the DC4_SLV register is set, then DC-DC4 comes under the control of the DC-DC3 registers,

and both converters are controlled together. All other DC-DC4 control registers have no effect when

DC4_SLV is set. Note that the DC4_SLV register can only be controlled via OTP/ICE configuration; it

cannot be changed by writing to the control register.

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