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參數(shù)資料
| 型號： | MC34940EGR2 |
| 廠商： | Freescale Semiconductor |
| 文件頁數(shù)： | 10/12頁 |
| 文件大小： | 0K |
| 描述： | IC IMAGING DEVICE ELEC 24-SOICW |
| 標準包裝： | 1,000 |
| 類型： | 圖像傳感器 |
| 輸入類型： | 邏輯 |
| 輸出類型： | 電壓 |
| 電流 - 電源： | 8mA |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 24-SOIC（0.295"，7.50mm 寬） |
| 供應商設備封裝： | 24-SOIC W |
| 包裝： | 帶卷 (TR) |
| 配用： | DEMO1985MC34940E-ND - KIT DEMO FOR MC34940E FAMILY |
Sensors
Freescale Semiconductor
7
MC34940
FEATURES
SHIELD DRIVER
A shield driver is included to minimize the electrode signal
along wires. This circuit provides a buffered version of the
returned AC signal from the electrode. Since it has nearly the
same amplitude and phase as the electrode signal, there is
little or no potential difference between the two signals
thereby canceling out any electric field. In effect, the shield
drive isolates the electrode signal from external virtual
grounds. A common application is to connect the Shield
Driver to the shield of a coax cable used to connect an
electrode to the corresponding electrode terminal. Another
typical use is to drive a ground plane that is used behind an
array of touch sensor electrodes in order to cancel out any
virtual grounds that could attenuate the AC signal.
TUNABLE FREQUENCY
The MC34940 offers 3 operating frequencies. In addition
to the default frequency of 120 kHz, the MC34940 has also
been characterized to work in two other frequencies (240 kHz
and 60 kHz) for applications with specific needs. These
frequencies are tunable by attaching a 20k and 82k resistor
at ROSC respectively. If a wider capacitance range is
needed, simply change the ROSC resistor value to 82k to
have the signal generator operate at 60 kHz which will extend
the capacitance range to 150 pF as seen on Figure 4. The
figure also shows that one can achieve higher sensitivity at
lower capacitances by setting the ROSC resistor value to
20k. All resistor values listed above are for 5% tolerance
resistors.
ADJUSTABLE RESPONSE TIME
The rectified sine wave is filtered by a Low Pass Filter
formed by an internal resistor and an external capacitor
attached to LP_CAP. The value of the external capacitor is
selected to allow the designer to optimize the balance
between noise and settling time. A typical value for the
external capacitor is 10 nF and in practice it will have a
response time of 2.5 ms. If faster response time is required a
1.0 nF capacitor can be used and it will have response times
around 500 s. Please note that reducing the LP_CAP
capacitor value increases noise accordingly.
Figure 4. Output Voltage vs. Capacitance at 3 Discrete Frequencies
Output Voltage vs Capacitance at 3 Discrete Frequencies
0
0.5
1
1.5
2
2.5
3
3.5
4
0
50
100
150
200
Capacitance (pF)
V
o
lt
ag
eO
u
tput
(V
ol
ts
)
120 kHz
240 kHz
60 kHz
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