PIC18LF24K22-I/SP Microchip Technology, PIC18LF24K22-I/SP Datasheet - Page 322
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PIC18LF24K22-I/SP
Manufacturer Part Number
PIC18LF24K22-I/SP
Description
IC PIC MCU 16KB FLASH 28SPDIP
Manufacturer
Microchip Technology
Series
PIC® XLP™ 18Fr
Specifications of PIC18LF24K22-I/SP
Core Size
8-Bit
Program Memory Size
16KB (8K x 16)
Core Processor
PIC
Speed
64MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, HLVD, POR, PWM, WDT
Number Of I /o
24
Program Memory Type
FLASH
Eeprom Size
256 x 8
Ram Size
768 x 8
Voltage - Supply (vcc/vdd)
1.8 V ~ 3.6 V
Data Converters
A/D 19x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
28-DIP (0.300", 7.62mm)
Controller Family/series
PIC18
No. Of I/o's
25
Eeprom Memory Size
256Byte
Ram Memory Size
768Byte
Cpu Speed
64MHz
No. Of Timers
7
Processor Series
PIC18LF
Core
PIC
3rd Party Development Tools
52715-96, 52716-328, 52717-734, 52712-325, EWPIC18
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Lead Free Status / RoHS Status
Lead free / RoHS Compliant, Lead free / RoHS Compliant
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capacitance, and the added capacitance of the human
PIC18(L)F2X/4XK22
19.3
The
measurements of capacitance and time, as well as for
accurate time delay. If the application only requires
measurement of a relative change in capacitance or
time, calibration is usually not necessary. An example of
this type of application would include a capacitive touch
switch, in which the touch circuit has a baseline
body changes the overall capacitance of a circuit.
If actual capacitance or time measurement is required,
two hardware calibrations must take place: the current
source needs calibration to set it to a precise current,
and the circuit being measured needs calibration to
measure and/or nullify all other capacitance other than
that to be measured.
19.3.1
The current source on board the CTMU module has a
range of ±60% nominal for each of three current
ranges. Therefore, for precise measurements, it is
possible to measure and adjust this current source by
placing a high precision resistor, R
analog channel. An example circuit is shown in
Figure 19-2. The current source measurement is
performed using the following steps:
1.
2.
3.
4.
5.
6.
The CTMU current source may be trimmed with the
trim bits in CTMUICON using an iterative process to get
an exact desired current. Alternatively, the nominal
value without adjustment may be used; it may be
stored by the software for use in all subsequent
capacitive or time measurements.
To calculate the value for R
must be chosen, and then the resistance can be
calculated. For example, if the A/D Converter reference
voltage is 3.3V, use 70% of full scale, or 2.31V as the
desired approximate voltage to be read by the A/D
Converter. If the range of the CTMU current source is
selected to be 0.55 A, the resistor value needed is cal-
culated as R
Similarly, if the current source is chosen to be 5.5 A,
R
source is set to 55 A.
DS41412A-page 322
CAL
Initialize the A/D Converter.
Initialize the CTMU.
Enable the current source by setting EDG1STAT
(CTMUCONL<0>).
Issue settling time delay.
Perform A/D conversion.
Calculate the current source current using
I = V/ R
resistance and V is measured by performing an
A/D conversion.
would be 420,000Ω, and 42,000Ω if the current
CTMU
Calibrating the CTMU Module
CURRENT SOURCE CALIBRATION
CAL
CAL
, where R
= 2.31V/0.55 A, for a value of 4.2 MΩ.
requires
CAL
calibration
CAL
is a high precision
, the nominal current
CAL
, onto an unused
for
precise
Preliminary
FIGURE 19-2:
A value of 70% of full-scale voltage is chosen to make
sure that the A/D Converter was in a range that is well
above the noise floor. Keep in mind that if an exact cur-
rent is chosen, that is to incorporate the trimming bits
from CTMUICON, the resistor value of R
to be adjusted accordingly. R
to allow for available resistor values. R
the highest precision available, keeping in mind the
amount of precision needed for the circuit that the
CTMU will be used to measure. A recommended
minimum would be 0.1% tolerance.
The following examples show one typical method for
performing a CTMU current calibration. Example 19-1
demonstrates how to initialize the A/D Converter and
the CTMU; this routine is typical for applications using
both modules. Example 19-2 demonstrates one
method for the actual calibration routine.
ANx
R
CAL
CTMU CURRENT SOURCE
CALIBRATION CIRCUIT
PIC18(L)FXXK22 Device
Current Source
2010 Microchip Technology Inc.
MUX
CAL
A/D Converter
may also be adjusted
A/D
CAL
CTMU
CAL
should be of
may need
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