WM8311 datasheet(72/302 Pages) WOLFSON

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WM8311

Pre-Production

PP, May 2012, Rev 3.1

15.4 OPERATING MODE CONTROL

15.4.1 DC-DC SYNCHRONOUS BUCK CONVERTERS

The DC-DC (Buck) Converters DC-DC1, DC-DC2 and DC-DC3 can be configured to operate in four

different operating modes. The operating modes are summarised in Table 33. For more detailed

information on the DC-DC (Buck) Converter operating modes, see Section 15.15.2.

DC-DC CONVERTER

OPERATING MODE

DESCRIPTION

Forced Continuous Conduction

Mode (FCCM)

High performance mode for all static and transient load

conditions.

Auto Mode: Continuous /

Discontinuous Conduction with

Pulse-Skipping Mode (CCM/DCM

with PS)

High efficiency mode for all static and transient load

conditions. Performance may be less than FCCM mode for

heavy load transients.

Hysteretic Mode

High efficiency mode for light static and light transient loads

only. Maximum load current is restricted; output voltage ripple

is increased.

LDO Mode

Power saving mode for light loads only. High efficiency for

ultra light loads. Low current soft-start control.

Table 33 DC-DC Synchronous Buck Converters Operating Modes

The operating mode of the DC-DC Converters in the ON power state is selected using the

DCm_ON_MODE register fields. The operating mode of the DC-DC Converters in the SLEEP power

state is selected using the DCm_SLP_MODE register fields.

When changing the operating mode of the DC-DC Converters in preparation for an increased load, a

set-up time of 100

s should be allowed for the operating mode to be established before applying the

new load.

Note that the operating mode of the DC-DC Converters may also be controlled by the Hardware

Control inputs. The Hardware Control inputs are alternate functions supported via GPIO. See

Section 15.9 for details of Hardware Control.

Note that, for minimum DC-DC3 quiescent current in LDO mode, the converter must first be enabled

in FCCM, CCM/DCM with PS or Hysteretic mode, before LDO mode is selected.

15.4.2 DC-DC BOOST CONVERTERS

The DC-DC4 Boost Converter is enabled by setting the DC4_ENA bit as described in Section 15.2.

Note that this Converter cannot be enabled automatically under timeslot control in the ON transition.

However, the Converter can either be disabled or unchanged in the SLEEP transition, as determined

by DC4_SLPENA.

The Boost Converter is intended to be used as a power supply for either of the Current Sinks, ISINK1

or ISINK2 (see Section 16). The Boost Converter must be configured for the applicable Current Sink

using the DC4_FBSRC bit.

When the DC-DC4 Boost Converter is enabled, its output voltage is regulated in such a way that the

selected ISINK voltage (at ISINK1 or ISINK2) is 0.5V. Output voltages of up to 30V can be generated

in order to support the current that has been selected for the ISINK. The required voltage range must

be set using the DC4_RANGE field in order to ensure stable operation.

If the Boost Converter is used to provide a supply for both ISINKs simultaneously, then the

DC4_RANGE and DC4_FBSRC bits should be set according to whichever of the ISINKs requires the

higher supply voltage.

15.4.3 LDO REGULATORS

The LDO Regulators LDO1 - LDO5 and LDO10 can be configured to operate in Normal operating

mode or in Low Power mode.

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