WM8948 Datasheet, PDF (90/189 Pages) Wolfson Microelectronics plc – Stereo Low-Power CODEC with Video Buffer and Touch Panel Controller

WM8948
AUXILIARY ADC
Production Data
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.
REGISTER
ADDRESS
R61 (3Dh)
AuxADC
Control
R62 (3Eh)
AuxADC
Source
BIT
LABEL
DEFAULT
DESCRIPTION
15
AUX_ENA
0
AUXADC Enable
0 = Disabled
1 = Enabled
14
AUX_CVT_ENA
0
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
8
AUX_BATT_SEL
0
AUXADC Battery (SPKVDD) input
select
0 = Disable Battery (SPKVDD)
measurement
1 = Enable Battery (SPKVDD)
measurement
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PD, May 2011, Rev 4.1
90