WM9712CLGEFLSLASHV datasheet(47/78 Pages) WOLFSON

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Production Data

WM9712L

PD, Rev 4.6, November 2011

AUXILIARY ADC INPUTS

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:



COMP1 / AUX1 (pin 29)



COMP2 / AUX2 (pin 30)



BMON / AUX3 (pin 31)



WIPER / AUX4 (pin 12)

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.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

76h

Touchpanel

Digitiser

Control

14:12

ADCSEL

000

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)

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.

BATTERY MEASUREMENT USING THE BMON/AUX3 PIN

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 30k

. 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 (20.83

s, assuming a 24.576MHz clock crystal is used). The

effective input impedance of BMON/AUX3 is therefore given by:

RBMON = 30k  48kHz / [BMON sampling rate]

For example, if BMON is sampled ten times per second, the effective input resistance is 30k

 

48kHz / 10Hz = 144M

.

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