WM8948ECSSLASHR datasheet(90/189 Pages) WOLFSON

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WM8948

Production Data

PD, May 2011, Rev 4.1

AUXILIARY ADC

The WM8948 incorporates a low-power 12-bit Auxiliary ADC (AUXADC). This can be used to

measure the SPKVDD supply voltage and to measure other analogue voltages connected to the

AUX1 or AUX2 inputs. The Auxiliary ADC is powered from LDOVDD - typically 3.3V.

The AUXADC is also used to perform Touch Panel measurements; these are interleaved with the

AUXADC measurement requests; see “Touch Panel Controller” for further details.

The AUXADC is powered on the TPVDD (internal) power domain; internal resistor dividers enable

SPKVDD voltages greater TPVDD to be measured by the AUXADC.

AUXADC CONTROL

The AUXADC is enabled by setting the AUX_ENA register bit.

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 WM8948 after each conversion request.

The AUXADC has 3 available input sources, which are SPKVDD, AUX1 and AUX2. Each of these

inputs is enabled by setting the respective bit in the AuxADC Source Register (R62). The WM8948

provides options to select the scaling and voltage reference for these inputs; these are described in

Table 58.

Note that the AUX1 and AUX2 pins should not be used as AUXADC inputs if they are used as audio

inputs. (See “Input Signal Path”.)

For each AUXADC measurement event (in Manual or Automatic modes), the WM8948 selects the

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

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

Automatic trigger.

The control fields associated with initiating AUXADC measurements are defined in Table 57.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R61 (3Dh)

AuxADC

Control

AUX_ENA

AUXADC Enable

0 = Disabled

1 = Enabled

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.

4:0

AUX_RATE [4:0]

0_0000

AUXADC Conversion Rate

0_0000 = Manual conversion

0_0001 = 16Hz

0_0010 = 32Hz

…(16Hz steps)

1_1111 = 496Hz

R62 (3Eh)

AuxADC

Source

AUX_BATT_SEL

AUXADC Battery (SPKVDD) input

select

0 = Disable Battery (SPKVDD)

measurement

1 = Enable Battery (SPKVDD)

measurement

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