WM8321 datasheet(97/253 Pages) WOLFSON

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Production Data

WM8321

PD, February 2012, Rev 4.0

18 AUXILIARY ADC

18.1 GENERAL DESCRIPTION

The WM8321 incorporates a 12-bit Auxiliary ADC (AUXADC). This can be used to perform a number

of system measurements (including supply voltages and battery temperature) and can also be used to

measure analogue voltages from external sources and sensors.

External inputs to the AUXADC should be connected to the pins GPIO10, GPIO11 and GPIO12. The

maximum voltage that can be measured is determined by the power domain associated with each;

this is selectable on a pin by pin basis as described in Section 21.3.

Note that, when GPIO10, GPIO11 or GPIO12 is used as an input to the AUXADC, then the normal

GPIO functionality cannot be supported on the affected pin(s). In this case, it is recommended that

the respective GPIO(s) are tri-stated, as described in Section 21.3.

18.2 AUXADC CONTROL

The AUXADC is enabled by setting the AUX_ENA register bit. By default, the AUXADC is not enabled

in the SLEEP state, but this can be selected using the AUX_SLPENA field.

The AUXADC measurements can be initiated manually or automatically. For automatic operation, the

AUX_RATE register is set according to the required conversion rate, and conversions are enabled by

setting the AUX_CVT_ENA bit. For manual operation, the AUX_RATE register is set to 00h, and each

manual conversion is initiated by setting the AUX_CVT_ENA bit. In manual mode, the

AUX_CVT_ENA bit is reset by the WM8321 after each conversion. (Note that the conversion result is

not available for readback until the AUXADC interrupt is asserted, as described in Section 18.5.)

The AUXADC has 5 available input sources. Each of these inputs is enabled by setting the respective

bit in the AuxADC Source Register (R16431).

For each AUXADC measurement event (in Manual or Automatic modes), the WM8321 selects the

next enabled input source. Any number of inputs may be selected simultaneously; the AUXADC will

measure each one in turn. Note that only a single AUXADC measurement is made on any Manual or

Automatic trigger.

For example, if the GPIO10, GPIO12 and PVDD voltages are enabled for AUXADC measurement,

then GPIO10 would be measured in the first instance, and GPIO12 then PVDD would be measured

on the next manual or automatic AUXADC triggers. In this case, a total of three manual or automatic

AUXADC triggers would be required to measure all of the selected inputs.

The control fields associated with initiating AUXADC measurements are defined in Table 45.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R16430

(402Eh)

AuxADC

Control

AUX_ENA

AUXADC Enable

0 = Disabled

1 = Enabled

Note - this bit is reset to 0 when the

OFF power state is entered.

AUX_CVT_ENA

AUXADC Conversion Enable

0 = Disabled

1 = Enabled

In automatic mode, conversions are

enabled by setting this bit.

In manual mode (AUX_RATE = 0),

setting this bit will initiate a

conversion; the bit is reset

automatically after each conversion.

AUX_SLPENA

AUXADC SLEEP Enable

0 = Disabled

1 = Controlled by AUX_ENA

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