WM8321 datasheet(137/253 Pages) WOLFSON

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Production Data

WM8321

PD, February 2012, Rev 4.0

137

27 VOLTAGE AND CURRENT REFERENCES

27.1 VOLTAGE REFERENCE (VREF)

The main voltage reference generated by the WM8321 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, as noted in Section 30.2. Omitting this capacitor will result in increased noise on the

voltage reference; this will particularly affect the analogue LDOs.

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

Auxiliary ADC function is 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 Auxiliary ADC is disabled. Enabling the Low Power Reference

mode will lead to a malfunction of the Auxiliary ADC function.

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 Auxiliary ADC is

disabled.

Table 83 Low Power Voltage Reference Control

27.2 CURRENT REFERENCE (IREF)

The Power Management circuits of the WM8321 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 WM8321 will malfunction if this

resistor is omitted.

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