WM8310 datasheet(71/291 Pages) WOLFSON

71 / 291 page

Pre-Production

WM8310

PP, May 2012, Rev 3.1

When LDO11_VSEL_SRC = 0, then the output voltage of LDO11 is set by LDO11_ON_VSEL (in the

ON state) or by LDO11_SLP_VSEL (in the SLEEP state) in the same way as the other LDOs.

When LDO11_VSEL_SRC = 1, the output voltage of LDO11 follows the output voltage of DC-DC

Converter 1. This enables both domains to be changed at the same time, eg. the processor core and

processor ‘alive’ domains. In this case, the LDO11 output voltage follows DC1_ON_VSEL or

DC1_SLP_VSEL in the ON state or SLEEP state respectively.

Note that, when LDO11_VSEL_SRC = 1, the LDO11 regulator adopts the nearest achievable output

voltage, which may not be identical to the DC-DC1 voltage, due to the more limited range and

resolution of LDO11 - the output voltage of LDO11 is in the range 0.8V to 1.55V in 50mV steps; the

output voltage of DC-DC1 is in the range 0.6V to 1.8V in 12.5mV steps. If DC-DC1 is disabled, then

the LDO11 voltage tracking feature is not supported, and the LDO11 output voltage will be 0.8V.

15.6 DC-DC SYNCHRONOUS BUCK CONVERTER CONTROL

Soft-Start control is provided for each of the DC-DC synchronous buck converters, using the

DCm_SOFT_START register fields. When a DC-DC Converter is switched on, the soft-start circuit will

apply current limiting in order to control the in-rush current. For DC-DC1 and DC-DC2, the current

limit is increased through up to 8 stages to the full load condition. The DCm_SOFT_START registers

select the duration of these stages. (Note that, under light loads, the full start-up may be achieved in

fewer than 8 stages.) A similar function is provided for DC-DC3, but only 3 intermediate stages are

implemented for this converter.

When DC-DC3 is operating in Hysteretic Mode, the maximum DC output current can be set using the

DC3_STNBY_LIM register. See Section 15.4.1 for details of the DC-DC3 operating modes.

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 15.9 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.

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