WM8351 datasheet(126/330 Pages) WOLFSON

126 / 330 page

WM8351

Production Data

PD, April 2012, Rev 4.5

126

14.6 CONFIGURING THE DC-DC CONVERTERS

The configuration of the DC-DC converters is described in the following sections. Some of the control

fields form part of the Custom Mode configuration settings and therefore will not require to be set in

software in some applications.

14.6.1

DC-DC CONVERTER ENABLE

The DC-DC Converters can be enabled in software using the register fields defined in Table 71. All

DC-DC converters include a soft-start feature that helps to reduce the inductor current at start up. In

order to further reduce supply in-rush current, individual converters should be programmed to start in

different time slots within the start-up sequence.

In the WM8351 ACTIVE state, the DC-DC Converters can be enabled in software using the

DCn_ENA bits. Setting these bits whilst in the Pre-Active state (see Figure 65) will not immediately

enable the corresponding DC-DC converter; these bits will only become effective once the WM8351

has reached the ACTIVE state.

Each Converter may be programmed to switch on in a selected timeslot within the start-up sequence.

The WM8351 will set the DCn_ENA field for any DC-DC converter that is enabled during the start-up

sequence. Note that setting the DCn_ENSLOT fields in software is only relevant to the Development

Mode, as these fields are assigned preset values in each of the Custom Modes.

Each Converter may be programmed to switch off in a selected timeslot within the shutdown

sequence. If a Converter is not allocated to one of the 14 shutdown timeslots, it will be disabled when

the WM8351 enters the OFF state.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

Note

: n is a number between 1 and 6 that identifies the individual DC-DC converter

R13 (0Dh) or

R176 (B0h)

0,1,2,3

DCn_ENA

Dependant on

CONFIG[1:0]

settings

DCDCn converter enable

0 = disabled

1 = enabled

Note: internal conditions may prevent

the converter from actually switching on

- see DCDC/LDO Status register for

actual converter status.

Note:

These bits can be accessed through R13 or through R176. Reading from or writing to either

R181 (B5h) for

DC-DC1

R184 (B8h) for

DC-DC2

R187 (BBh) for

DC-DC3

R190 (BEh) for

DC-DC4

13:10

DCn_ENSLO

T [3:0]

Dependant on

CONFIG[1:0]

settings

Time slot for DC-DCn start-up

0000 = Disabled (do not start up)

0001 = Start-up in time slot 1

… (total 14 slots available)

1110 = Start-up in time slot 14

1111 = Start up on entering ACTIVE

9:6

DCn_SDSLO

T [3:0]

0000

Time slot for DC-DCn shutdown.

0000 = Shut down on entering OFF

0001 = Shutdown in time slot 1

…. (total 14 slots available)

1110 = Shutdown in time slot 14

1111 = Shut down on entering OFF

Note: n

is number between 1 and 4 that identifies the individual DC-DC converter

Table 71 Enabling and Disabling the DC-DC Converters

14.6.2

CLOCKING

The DC-DC converters are controlled by an internally generated clock signal from the RC Oscillator

with a constant frequency of around 2.0MHz for DC-DC 1, 3 and 4, and a constant frequency of

around 1.0MHz for DC-DC 2.

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