PIC16F1513T-I/SS View Datasheet(PDF) - Microchip Technology
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Description
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PIC16F1513T-I/SS Datasheet PDF : 360 Pages
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PIC16(L)F1512/3
16.5 Hardware Capacitive Voltage
Divider (CVD) Module
The hardware Capacitive Voltage Divider (CVD)
module is a peripheral which allows the user to perform
a relative capacitance measurement on any ADC
channel using the internal ADC sample and hold
capacitance as a reference. This relative capacitance
measurement can be used to implement capacitive
touch or proximity sensing applications.
The CVD operation begins with the ADC’s internal
sample and hold capacitor (CHOLD) being disconnected
from the path which connects it to the external
capacitive sensor node. While disconnected, CHOLD is
pre-charged to VDD or VSS while the path to the sensor
node is also discharged to VDD or VSS – typically this
node is discharged to the level opposite that of CHOLD.
When the pre-charge phase is complete, the VDD/VSS
bias paths for the two nodes are shut off and CHOLD
and the path to the external sensor node are
re-connected, at which time the acquisition phase of
the CVD operation begins. During acquisition, a
capacitive voltage divider is formed between the
pre-charged CHOLD and sensor nodes which results in
a final voltage level settling on CHOLD which is
determined by the capacitances and pre-charge levels
of the two nodes involved. After acquisition, the ADC
converts the voltage level held on CHOLD. This process
is then usually repeated with the selected pre-charge
levels for both the CHOLD and sensor nodes inverted.
Figure 16-6 shows the waveform for two inverted CVD
measurements, which is also known is differential CVD
measurement.
In a typical application, an Analog-to-Digital Converter
(ADC) channel is attached to a pad on a Printed Circuit
Board (PCB), which is electrically isolated from the end
user. A capacitive change is detected on the ADC
channel using the CVD conversion method when the
end user places a finger over the PCB pad, the
developer then can implement software to detect a
touch or proximity event or change. Key features of this
module include:
• Automated double sample conversions
• Two result registers
• Inversion of second sample
• 7-bit pre-charge timer
• 7-bit acquisition timer
• Two guard ring output drives
• Adjustable sample and hold capacitor array
Note:
For more information on capacitive
voltage divider sensing method refer to
the Application Note AN1478, “mTouchTM
Sensing Solution Acquisition Methods
Capacitive Voltage Divider” (DS01478).
FIGURE 16-6:
VDD
DIFFERENTIAL CVD MEASUREMENT WAVEFORM
Precharge
Acquisition
Conversion Precharge
Acquisition
Conversion
VSS
First Sample
Second Sample
Time
2012-2014 Microchip Technology Inc.
DS40001624C-page 137
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