WM8311 datasheet(173/302 Pages) WOLFSON

173 / 302 page

Pre-Production

WM8311

PP, May 2012, Rev 3.1

173

27 VOLTAGE AND CURRENT REFERENCES

27.1 VOLTAGE REFERENCE (VREF)

The main voltage reference generated by the WM8311 is bonded to the VREFC pin. The accuracy of

this reference is optimised by factory-set trim registers.

The voltage reference (VREF) requires an external decoupling capacitor; a 100nF X5R capacitor is

recommended for typical applications, as noted in Section 30.2. If USB100MA_STARTUP=1X (see

Section 17.4), then a 50nF capacitor should be used. Omitting this capacitor will result in increased

noise on the voltage reference; this will particularly affect the analogue LDOs.

The VREFC capacitor should be grounded to the REFGND pin.

The voltage reference circuit includes a low-power mode, which enables power consumption to be

minimised where appropriate. The low-power reference mode may lead to increased noise on the

voltage reference; this mode should only be selected when minimum power consumption is more

important than voltage stability. Note that the Low Power Reference mode is not supported when the

Touch Panel or Auxiliary ADC functions are enabled.

The Low Power Reference mode is enabled when REF_LP register is set. The Low Power Reference

mode should only be enabled when the Touch Panel and Auxiliary ADC are both disabled. Enabling

the Low Power Reference mode will lead to a malfunction of the Touch Panel or Auxiliary ADC

functions.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R16387

(4003h)

REF_LP

Low Power Voltage Reference Control

0 = Normal

1 = Low Power Reference Mode select

Note that Low Power Reference Mode is

only supported when the Touch Panel and

Auxiliary ADC are both disabled.

Table 113 Low Power Voltage Reference Control

27.2 CURRENT REFERENCE (IREF)

The Power Management circuits of the WM8311 use an integrated current reference.

This current reference (IREF) requires the connection of an external resistor to the IREFR pin; a

100k

 (1%) resistor is recommended, as noted in Section 30.2. The WM8311 will malfunction if this

resistor is omitted.

The IREFR resistor should be grounded to the REFGND pin.

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