wm9712l Wolfson Microelectronics plc, wm9712l Datasheet - Page 47

• Manufacturer Part Number: wm9712l
• Description: Ac?97 Audio And Touchpanel Codec
• Manufacturer: Wolfson Microelectronics plc

Production Data
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AUXILIARY ADC INPUTS
BATTERY MEASUREMENT USING THE BMON/AUX3 PIN
The ADC used for touchpanel digitisation can also be used for auxiliary measurements, provided that
it is enabled (register 78h, PRP = 11). The WM9712L has four pins that can be used as auxiliary
ADC inputs:
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•
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Note that pin 12 connects to the wiper of a 5-wire touchpanel wiper function. Auxiliary measurements
taken on pin 12 are only meaningful when it is not connected to a touchpanel (i.e. a 4-wire
touchpanel, or no touchpanel at all, is used). Pins 29 and 30 are also used as comparator inputs (see
Battery Alarm and Battery Measurement), but auxiliary measurements can still be taken on these
pins at any time. For the use of pin 31 see the “Battery Alarm And Battery Measurement” section,
note that the measured value from the BMON/AUX3 pin will be 1/3 of the actual value due to the
potential divider on this pin. The ADCSEL control bits select between different ADC inputs, as shown
below.
Table 34 Auxiliary ADC Measurements
Auxiliary ADC measurements are initiated in the same way as touchpanel measurements, and the
data is returned in the same manner. Please refer to the “Controlling the Touchpanel Interface”
section.
BMON/AUX3 (pin 31) has the capability to take inputs up to 5 volts (Assuming AVDD=3.3V) by
dividing down the input signal. The internal potential divider has a total resistance of 30kΩ. However,
it is only connected to the pin when an AUX3 measurement is requested, and remains connected for
the duration of one AC-Link frame (20.83µs, assuming a 24.576MHz clock crystal is used). The
effective input impedance of BMON/AUX3 is therefore given by:
R
For example, if BMON is sampled ten times per second, the effective input resistance is 30kΩ ×
48kHz / 10Hz = 144MΩ.
BMON
76h
Touchpanel
Digitiser
Control
REGISTER
ADDRESS
COMP1 / AUX1 (pin 29)
COMP2 / AUX2 (pin 30)
BMON / AUX3 (pin 31)
WIPER / AUX4 (pin 12)
= 30kΩ × 48kHz / [BMON sampling rate]
14:12
BIT
ADCSEL
LABEL
000
DEFAULT
Touchpanel ADC Input Selector
000: No measurement
001-011: Touchpanel measurement (please
refer to Touchpanel Digitiser section)
100: COMP1 / AUX1 measurement (pin 29)
101: COMP2 AUX2 measurement (pin 30)
110: BMON / AUX3 measurement (pin 31)
111: WIPER / AUX 4 measurement (pin 12)
DESCRIPTION
PD Rev 4.5 August 2006
WM9712L
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