Production Data
WM8945
For SPKVDD measurement, the SPKVDD voltage is connected to a potential divider in order to
reduce it to a suitable level. Two different scaling factors are available, controlled by the
AUX_BATT_SCALE register bit. The scaling factor should be selected such that the scaled output is
less than the maximum measurable level (LDOVDD).
For optimum measurement of the SPKVDD voltage, the SPKVDD potential divider can be connected
to the AUX1 pin, allowing an external capacitor to be used to filter noise from the SPKVDD supply.
This is enabled by setting the AUX_AUX1_FILTB register bit. This option can only be used when
AUX1 is not also used as an input to the AUXADC.
REGISTER
ADDRESS
BIT
LABEL
BG_ENA
DEFAULT
DESCRIPTION
R54 (36h)
Bandgap
0
Bandgap Reference Control
0 = Disabled
15
1 = Enabled
R63 (3Fh)
AUX_AUX1_
FILTB
AUXADC Battery (SPKVDD)
measurement filter control
9
0
AuxADC
Config
0 = Disabled
1 = Enabled
When AUX_AUX1_FILTB is set, the
Battery (SPKVDD) measurement
point is connected to the AUX1 pin,
allowing an external capacitor to be
used to filter noise.
AUX_BATT_
SCALE
AUXADC Battery (SPKVDD)
measurement divider control
8
1
0 = 0.45 x SPKVDD
(Note that 0.45 x 3.3V = 1.485V)
1 = 0.41 x SPKVDD
(Note that 0.41 x 3.6V = 1.476V)
AUXADC AUX2 reference select
0 = LDOVDD/2
AUX_AUX2_
REF
1
0
0
0
1 = 1.5V (nominal) Bandgap
AUXADC AUX1 reference select
0 = LDOVDD/2
AUX_AUX1_
REF
1 = 1.5V (nominal) Bandgap
Table 57 AUXADC Input Configuration
AUXADC READBACK
Measured data from the AUXADC is read via the AuxADC Data Register (R60), which contains two
fields. The AUXADC Data Source is indicated in the AUX_DATA_SRC field; the associated
measurement data is contained in the AUX_DATA field.
Reading from the AuxADC Data Register returns a 12-bit code which represents the most recent
AUXADC measurement on the associated channel. It should be noted that every time an AUXADC
measurement is written to the AuxADC Data Register, the previous data is overwritten – the host
processor should ensure that data is read from this register before it is overwritten.
The 12-bit AUX_DATA field can be equated to the actual voltage by scaling according to the
applicable reference source. The full-scale value of AUX_DATA corresponds to the LDOVDD voltage
level.
The AUXADC interrupts can be used to indicate when new data is available – see “Interrupts”. A
GPIO pin configured as “AUX_DONE” can also be used to indicate when new data is available – see
“General Purpose Input / Output”.
PD, May 2011, Rev 4.1
85
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
