參數(shù)資料
型號: AD7873ARUZ
廠商: ANALOG DEVICES INC
元件分類: 消費家電
英文描述: Touch Screen Digitizer
中文描述: SPECIALTY CONSUMER CIRCUIT, PDSO16
封裝: LEAD FREE, MO-153AB, TSSOP-16
文件頁數(shù): 17/28頁
文件大?。?/td> 657K
代理商: AD7873ARUZ
AD7873
Battery Measurement
The AD7873 can monitor a battery voltage from 0 V to 6 V.
Figure 31 shows a block diagram of a battery voltage monitored
through the V
BAT
pin. The voltage to the +V
CC
of the AD7873 is
maintained at the desired supply voltage via the dc/dc regulator
while the input to the regulator is monitored. This voltage on
V
BAT
is divided by 4 so that a 6 V battery voltage is presented to
the ADC as 1.5 V. To conserve power, the divider is on only
during the sampling of a voltage on V
BAT
. Table 5 shows the
control bit settings required to perform a battery measurement.
Rev. D | Page 17 of 28
0
+
BATTERY
0V TO 6V
DC/DC
CONVERTER
+V
CC
V
BAT
0V TO 1.5V
ADC CORE
7.5k
2.5k
Figure 31. Block Diagram of Battery Measurement Circuit
Pressure Measurement
The pressure applied to the touch screen via a pen or finger can
also be measured with the AD7873 with some simple calcula-
tions. The 8-bit resolution mode would be sufficient for this
measurement, but the following calculations are shown with the
12-bit resolution mode. The contact resistance between the X
and Y plates is measured, which provides a good indication of
the size of the depressed area and the applied pressure. The area
of the spot touched is proportional to the size of the object
touching it. The size of this resistance (R
TOUCH
) can be calculated
using two different methods.
The first method requires the user to know the total resistance
of the X-plate tablet. Three touch screen conversions are
required, a measurement of the X-position, Z
1
-position, and Z
2
-
position (see Figure 32). The following equation calculates the
touch resistance:
(
) (
×
=
POSITION
XPLATE
TOUCH
X
R
R
) (
×
)
[
]
1
/
4095
/
1
2
Z
Z
The second method requires that the resistance of both the
X-plate and Y-plate tablets are known. Again three touch screen
conversions are required, a measurement of the X-position,
Y-position, and Z
1
-position (see Figure 32).
The following equation also calculates the touch resistance:
(
{
YPLATE
R
) (
×
)(
[
)
]
}
(
)
}
4095
/
1
/
4096
4095
/
/
POSITION
Y
1
POSITION
1
XPLATE
TOUCH
R
Z
X
×
Z
R
=
+
+
+
0
X+
X–
X+
X–
Y+
Y–
Y–
TOUCH
TOUCH
Z
2
-POSITION
Z
1
-POSITION
TOUCH
X-POSITION
Y+
X+
X–
Y–
Y+
MEASURE X-POSITION
MEASURE Z
1
-POSITION
MEASURE Z
2
-POSITION
Figure 32. Pressure Measurement Block Diagram
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