WM8311 datasheet(122/302 Pages) WOLFSON

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WM8311

Pre-Production

PP, May 2012, Rev 3.1

122

18 AUXILIARY ADC

18.1 GENERAL DESCRIPTION

The WM8311 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 AUXADCIN1, AUXADCIN2,

AUXADCIN3 and AUXADCIN4. The maximum voltage that can be measured is determined by the

power domain associated with each (see Section 3). In the case of AUXADCIN 1-3, the maximum

voltage is SYSVDD; in the case of AUXADCIN4, the maximum voltage is TPVDD. Note that SYSVDD

varies according to the voltage of the preferred power source (WALLVDD, USBVDD or BATTVDD).

The AUXADC can also measure the voltage on WALLVDD, USBVDD and BATTVDD. Internal

resistor dividers enable voltages higher than SYSVDD to be measured by the AUXADC - voltages up

to 6V can be measured on these pins.

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 WM8311 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.)

Note that the AUXADC measurements are interleaved with the Touch Panel measurements, when

both are enabled. If a Touch Panel measurement set is already in progress at the time when an

AUXADC measurement is due, then the AUXADC measurement will be delayed until after the Touch

Panel measurement set has completed. This applies equally to Manual and to Automatic AUXADC

modes.

The AUXADC has 10 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 WM8311 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 AUX1, BATT and USB voltages are enabled for AUXADC measurement, then

AUX1 would be measured in the first instance, and BATT then USB 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 65.

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