AD7147ACPZ-500RL7(Rev0) 데이터 시트보기 (PDF) - Analog Devices
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AD7147ACPZ-500RL7
(Rev.:Rev0)
(Rev.:Rev0)
Analog Devices
AD7147ACPZ-500RL7 Datasheet PDF : 68 Pages
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AD7147
Registering a Sensor Activation
When a user approaches a sensor, the total capacitance associated
with that sensor changes and is measured by the AD7147. If
the change causes a set threshold to be exceeded, the AD7147
interprets this as a sensor activation.
On-chip threshold limits are used to determine when a sensor
activation occurs. Figure 20 shows the change in CDC_RESULT_Sx
when a user activates a sensor. The sensor is deemed to be active
only when the value of CDC_RESULT_Sx is either greater than the
value of STAGEx_HIGH_THRESHOLD or less than the value
of STAGEx_LOW_THRESHOLD.
SENSOR ACTIVE (A)
STAGEx_HIGH_THRESHOLD
CDC_RESULT_Sx
AMBIENT OR
NO-TOUCH VALUE
STAGEx_LOW_THRESHOLD
SENSOR ACTIVE (B)
Figure 20. Sensor Activation Thresholds
In Figure 20, two sensor activations are shown. Sensor Active A
occurs when a sensor is connected to the positive input of the
converter. In this case, when a user activates the sensor, there is an
increase in CDC code, and the value of CDC_RESULT_Sx exceeds
that of STAGEx_HIGH_THRESHOLD. Sensor Active B occurs
when the sensor is connected to the negative input of the converter.
In this case, when a user activates the sensor, there is a decrease
in CDC code, and the value of CDC_RESULT_Sx becomes less
than the value of STAGEx_LOW_THRESHOLD.
For each conversion stage, the STAGEx_HIGH_THRESHOLD
and STAGEx_LOW_THRESHOLD registers are in Register Bank
3. The values in these registers are updated automatically by the
AD7147 due to its environmental calibration and adaptive
threshold logic.
At power-up, the values in the STAGEx_HIGH_THRESHOLD
and STAGEx_LOW_THRESHOLD registers are the same as those
in the STAGEx_OFFSET_HIGH and STAGEx_OFFSET_LOW
registers in Bank 2. The user must program the STAGEx_OFFSET
_HIGH and STAGEx_OFFSET_LOW registers on device power-
up. See the Environmental Calibration section of the data sheet
for more information.
Complete Solution for Capacitance Sensing
Analog Devices, Inc., provides a complete solution for
capacitance sensing. The two main elements to the solution are
the sensor PCB and the AD7147.
If the application requires high resolution sensors such as scroll
bars or wheels, software is required that runs on the host
processor. The memory requirements for the host depend on
the sensor and are typically 10 kB of code and 600 bytes of data
memory, depending on the sensor type.
SENSOR PCB
AD7147
SPI OR I2C
HOST PROCESSOR
1 MIPS
10kB ROM
600 BYTES RAM
Figure 21. Three-Part Capacitance-Sensing Solution
Analog Devices supplies the sensor PCB footprint design
libraries to the customer and supplies any necessary software on
an open-source basis.
BIAS PIN
This pin is connected internally to a bias node of the AD7147.
To ensure correct operation of the AD7147 connect a 10 nF
capacitor between the BIAS pin and ground. The voltage seen at
the BIAS pin is VCC/2.
OPERATING MODES
The AD7147 has three operating modes. Full power mode, where
the device is always fully powered, is suited for applications where
power is not a concern (for example, game consoles that have an
ac power supply). Low power mode, where the part automatically
powers down when no senosr is active, is tailored to provide
significant power savings compared with full power mode and
is suited for mobile applications, where power must be
conserved. In shutdown mode, the part shuts down completely.
The POWER_MODE bits (Bit 0 and Bit 1) of the control
register set the operating mode on the AD7147. The control
register is at Address 0x000. Table 8 shows the POWER_MODE
settings for each operating mode. To put the AD7147 into
shutdown mode, set the POWER_MODE bits to either 01 or 11.
Table 8. POWER_MODE Settings
POWER_MODE Bits
Operating Mode
00
Full power mode
01
Shutdown mode
10
Low power mode
11
Shutdown mode
The power-on default setting of the POWER_MODE bits is 00,
full power mode.
Rev. 0 | Page 12 of 68
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