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參數(shù)資料
| 型號： | AD7873ACP |
| 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, QCC16 |
| 封裝： | 4 X 4 MM, MO-220VGGC, LFCSP-16 |
| 文件頁數(shù)： | 16/28頁 |
| 文件大?。?/td> | 657K |
| 代理商： | AD7873ACP |
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AD7873
supply the external touch screen can be turned off once the
acquisition is complete, resulting in a power savings. However,
the on-resistance of the Y drivers affects the input voltage that
can be acquired. The full touch screen resistance could be in the
order of 200 to 900 , depending on the manufacturer. Thus,
if the on-resistance of the switches is approximately 6 , true
full-scale and zero-scale voltages cannot be acquired, regardless
of where the pen/stylus is on the touch screen. Note that the
minimum touch screen resistance recommended for use with
the AD7873 is approximately 70 . In this mode of operation,
therefore, some voltage is likely to be lost across the internal
switches, and it is unlikely that the internal switch resistance
will track the resistance of the touch screen over temperature
and supply, providing an additional source of error.
Rev. D | Page 16 of 28
0
+V
CC
V
REF
GND
Y+
Y–
X+
IN+
IN+
IN–
REF+
ADC CORE
REF–
Figure 28. Single-Ended Reference Mode (SER/DFR = 1)
The alternative to this situation is to set the SER/DFR bit low.
Again, making a Y coordinate measurement is considered, but
now the +REF and –REF nodes of the ADC are connected
directly to the Y+ and Y– pins. This means the analog-to-digital
conversion is ratiometric. The result of the conversion is always
a percentage of the external resistance, independent of how it
could change with respect to the on resistance of the internal
switches. Figure 29 shows the configuration for a ratiometric Y
coordinate measurement.
0
+V
CC
GND
Y+
Y–
X+
IN+
IN+
IN–
REF+
ADC CORE
REF–
Figure 29. Differential Reference Mode (SER/DFR = 0)
The disadvantage of this mode of operation is that during both
the acquisition phase and conversion process, the external touch
screen must remain powered. This results in additional supply
current for the duration of the conversion.
MEASUREMENTS
Temperature Measurement
Two temperature measurement options are available on the
AD7873, the single conversion method and the differential
conversion method. Both methods are based on an on-chip
diode measurement.
In the single conversion method, a diode voltage is digitized and
recorded at a fixed calibration temperature. Any subsequent
polling of the diode provides an estimate of the ambient tem-
perature through extrapolation from the calibration temperature
diode result. This assumes a diode temperature drift of
approximately –2.1 mV/°C. This method provides a resolution
of approximately 0.3°C and a predicted accuracy of ±3°C.
The differential conversion method is a 2-point measurement.
The first measurement is performed with a fixed bias current
into a diode, and the second measurement is performed with a
fixed multiple of the bias current into the same diode. The
voltage difference in the diode readings is proportional to
absolute temperature and is given by the following formula:
(
N
ln
q
T
V
BE
/
)
(
×
)
=
κ
where
V
BE
represents the diode voltage,
N
is the bias current
multiple,
k
is Boltzmann’s constant and
q
is the electron charge.
This method provides more accurate absolute temperature
measurement of ± 2°C. However, the resolution is reduced to
approximately 1.6°C. Assuming a current multiple of 105
(which is typical for the AD7873) taking Boltzmann’s constant,
k
= 1.38054 ×10
–23
electrons volts/degrees Kelvin, the electron
charge
q
= 1.602189 × 10
–19
, then
T
, the ambient temperature in
degrees centigrade, would be calculated as follows:
(
(
N
ln
q
V
T
BE
273
10
49
.
×
×
=
°
)
(
)
(
/
3
)
)
Κ
V
C
T
N
ln
×
q
T
×
V
=
BE
BE
/
×
κ
=
κ
V
BE
is calculated from the difference in readings from the first
conversion and second conversion.
Figure 30 shows a block diagram of the temperature
measurement mode.
0
I
TEMP0
TEMP1
105*I
MUX
ADC
Figure 30. Block Diagram of Temperature Measurement Circuit
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AD7873ACPZ | Touch Screen Digitizer |
| AD7873ACPZ3 | 10-Bit, 60 MSPS ADC SE/Diff, Int/Ext Ref., program. i/p range w/Pwrdown, comp. to ADS822/4/5/6/8 28-SSOP |
| AD7873ARQ | 10-Bit, 60 MSPS ADC SE/Diff, Int/Ext Ref., program. i/p range w/Pwrdown, comp. to ADS822/4/5/6/8 28-SSOP |
| AD7873ARU | Touch Screen Digitizer |
| AD7873ARUZ | Touch Screen Digitizer |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD7873ACP-REEL | 制造商:Analog Devices 功能描述:TOUCH SCREEN DIGITIZER |
| AD7873ACP-REEL7 | 制造商:Analog Devices 功能描述:TOUCH SCREEN DIGITIZER |
| AD7873ACPZ | 功能描述:IC ADC 12BIT TOUCHSCREEN 16LFCSP RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 觸摸屏控制器 系列:- 標(biāo)準(zhǔn)包裝:96 系列:- 類型:- 觸摸面板接口:- 輸入數(shù)/鍵:- 分辨率（位）:- 評估套件:* 數(shù)據(jù)接口:- 數(shù)據(jù)速率/采樣率 (SPS，BPS):- 電壓基準(zhǔn):- 電源電壓:- 電流 - 電源:- 工作溫度:- 安裝類型:表面貼裝 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:16-TSSOP 包裝:帶卷 (TR) |
| AD7873ACPZ3 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Touch Screen Digitizer |
| AD7873ACPZ-REEL | 功能描述:IC ADC 12BIT TOUCHSCREEN 16LFCSP RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 觸摸屏控制器 系列:- 標(biāo)準(zhǔn)包裝:96 系列:- 類型:- 觸摸面板接口:- 輸入數(shù)/鍵:- 分辨率（位）:- 評估套件:* 數(shù)據(jù)接口:- 數(shù)據(jù)速率/采樣率 (SPS，BPS):- 電壓基準(zhǔn):- 電源電壓:- 電流 - 電源:- 工作溫度:- 安裝類型:表面貼裝 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:16-TSSOP 包裝:帶卷 (TR) |
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