WM8351 datasheet(130/330 Pages) WOLFSON

130 / 330 page

WM8351

Production Data

PD, April 2012, Rev 4.5

130

A summary of the Mode Control and Voltage Control for DC-DC Converter 1 is provided in Table 76.

Note that “Hibernate” in Table 76 refers to a GPIO Hibernate input or to the applicable Hibernate

signal selected by the DC1_HIB_TRIG field.

The equivalent logic applies for DC-DC 3 and 4. Note that the DC-DC Converters must also be

enabled as described in Table 71.

HIBERNATE

DC1_HIB_MODE

DC1_SLEEP

DC1_ACTIVE

OPERATING

MODE

OUTPUT

VOLTAGE

Standby/Hysteretic

DC1_VSEL

Active

DC1_VSEL

LDO Mode

DC1_VSEL

000

Standby/Hysteretic

DC1_VSEL

Active

DC1_VSEL

LDO Mode

DC1_VSEL

001

Standby/Hysteretic

DC1_VIMG

Active

DC1_VIMG

LDO Mode

DC1_VIMG

010

Standby/Hysteretic

DC1_VSEL

011

Standby/Hysteretic

DC1_VIMG

100

LDO Mode

DC1_VSEL

101

LDO Mode

DC1_VIMG

110

Disabled

N/A

111

Disabled

N/A

Table 76 DC1 Converter Operating Mode Selection

14.6.4

DC-DC BOOST (STEP-UP) CONVERTER CONTROL

DC-DC Converter 2 is a boost converter which can be configured to operate in different operating

modes, using the register bits described in Table 77.

In Switch mode, the DC-DC Converter acts as a switch between VP2 and L2. The switch is enabled

(closed) by setting DC2_ENA = 1. The switch is disabled (opened) by setting DC2_ENA = 0. Note that

the switch voltage source on VP2 must be >1.2V to ensure reliable operation.

In Boost mode, the DC-DC Converter operates as a step-up converter, employing current-mode

architecture, capable of powering LED lights. The output voltage can be higher than the input voltage,

but cannot be lower. Different configurations of voltage feedback are available in boost mode, to

control the output voltage in different ways. The voltage feedback mode is selected by the

DC2_FBSRC register field.

When DC2_FBSRC = 00, the converter’s output voltage is set by two external resistors connected to

FB2. See Section 29 for Applications Information covering the selection of suitable components.

When DC2_FBSRC = 01, the converter uses the ISINKA pin as feedback and adjusts its output

voltage in order to achieve the required ISINKA current.

When DC2_FBSRC = 11, the converter’s output voltage is set by two internal resistors, resulting in a

fixed 5V output, suitable for USB interfaces.

The current-controlled configuration using ISINKA is intended for controlling a string of serially-

connected LEDs driven by the DC-DC boost converter. See Table 97 for a definition of the CS1_ISEL

connected on the FB2 pin determine the maximum output voltage. See Section 29 for Applications

Information covering the selection of suitable components.

In all configurations, the input pin VP2 must be externally wired to one of the supply rails, BATT or

LINE. Using LINE has the advantage that the converters can operate when the battery is flat,

defective or absent. Note that VP2 should not be connected to the USB supply rail.

The DC2_RMPH and DC2_RMPL bits defined in Table 77 should be set according to the desired

output voltage in order to optimise the transient response of the converter. Selecting a different value

could result in sub-harmonic oscillation of the converter.

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