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CapTIvate™ Touch Getting Started Manual
17
Copyright © 2021, Texas Instruments Incorporated
4.2
Hardware design
4.2.1
Schematic design
The main concern of the schematic design is whether the MCU function is normal, and EMC anti-noise
performance. Table 4-3 is a checklist for schematic design. For specific design solutions, please refer to the
corresponding device datasheet, or refer to the EVM schematic diagram in
of this manual.
Table 4-3 Schematic Design Checklist
Number Classification
Component
Recommendation
1
Smallest
system
Reset and programming
circuit
Add 47kΩ pull
-up resistor and 1nF pull-down capacitor to
Reset pin.
2
Power supply circuit
Add 10µF and 0.1µF capacitors to VCC and GND, and place
them close to the MCU.
3
Capacitive
touch
VREG filter circuit
Add 1µF capacitance to ground close to VREG pin, ESR ≤
200mΩ
.
4
Series resistance on CAP I/O
Add a 470Ω
-
10kΩ resistor close to the MCU pin for ESD
protection and anti-noise filtering.
5
CAP I/O pin assignment (if
possible)
It is recommended to use the “Auto
-
Assign” function of
CapTIvate™ Design Center to assign CAP I/O pins.
Note:
In
addition to buttons and proximity sensors, scroll wheels,
sliders, and touch panels have sequence requirements for
scanning CAP I/O. It is strongly recommended to use the
Auto-Assign function to assign scroll wheels, sliders, and
touch panel CAPs after configuring the buttons. I/O pin.
6
EMC anti-
noise
(Optional)
EMC filter capacitor
For mutual-capacitive applications, add 68pF of capacitance
to ground between the series resistance on the RX pin and
the sensor electrode.
7
TVS diode
Add a 3.3V TVS tube with low leakage and low parasitic
capacitance between the CAP I/O series resistance and the
electrode.
Add a general TVS tube to the power supply and external
connection line.
8
Common mode
inductors/magnetic beads
Add common mode inductance and magnetic beads to the
power supply as needed.
9
others
I2C communication line pull-
up resistor
Add 2.2kΩ
pull-up resistor.
10
I2C communication pins (GUI
default configuration)
MSP430FR25x2
：
P2.4: IRQ (OPEN DRAIN)
P2.5: UCB0 I2C SDA
P2.6: UCB0 I2C SCL
MSP430FR263x/253x/267x
：
P1.1: IRQ (OPEN DRAIN)
P1.2: UCB0 I2C SDA
P1.3: UCB0 I2C SCL
11
UART communication pin
(GUI default configuration)
MSP430FR25x2
：
P2.0: UCA0 UART TXD
P2.1: UCA0 UART RXD
MSP430FR263x/253x/267x
：
P1.4: UCA0 UART TXD
P1.5: UCA0 UART RXD
12
Boot Loader (BSL)
For BSL pin definition, please refer to the Bootloader chapter
in the corresponding device datasheet.
13
Button to MCU connector
Will increase the parasitic capacitance to the ground, it is
not recommended to use.
14
Test point
Increase the related test points of VCC, GND,
communication port.
For the EMC anti-noise design, during the preliminary evaluation, it is recommended to reserve the welding
position of the corresponding component as needed, and select the welding according to the final test result.
What is important to explain is the choice of series resistance on CAP I/O. Because the series resistance will affect
the base capacitance and the capacitance change caused by the touch at the same time, the series resistance itself
will not affect the sensitivity of the button. Since it forms a low-pass filter with parasitic capacitance, a larger series
