SLAU857A May   2021  – July 2021 MSP430FR2476 , MSP430FR2512 , MSP430FR2522 , MSP430FR2532 , MSP430FR2533 , MSP430FR2632 , MSP430FR2633 , MSP430FR2672 , MSP430FR2673 , MSP430FR2675 , MSP430FR2676

 

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4.2.1 Schematic Design

The main concern of the schematic design is both to ensure that the MCU function is normal and to maximize EMC anti-noise performance. Table 4-3 is a checklist for schematic design. For specific design solutions, refer to the device-specific data sheet, or refer to the EVM schematic diagram in Section 3.3.

Table 4-3 Schematic Design Checklist
NumberClassificationComponentRecommendation
1Smallest systemReset and programming circuitAdd 47-kΩ pullup resistor and 1-nF pulldown capacitor to Reset pin.
2Power supply circuitAdd 10-µF and 0.1-µF capacitors to VCC and GND, and place them close to the MCU.
3Capacitive touchVREG filter circuitAdd 1-µF capacitance to ground close to VREG pin, ESR ≤200 mΩ.
4Series resistance on CAP I/OAdd a 470-Ω to 10-kΩ resistor close to the MCU pin for ESD protection and anti-noise filtering.
5CAP 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.

In addition to buttons and proximity sensors, scroll wheels, sliders, and touch panels have sequence requirements for scanning the CAP I/O pins. The Auto-Assign function includes this sequence to assign scroll wheels, sliders, and touch panel CAP I/O pins after configuring the buttons.

6EMC anti-noise (Optional)EMC filter capacitorFor mutual-capacitive applications, add 68 pF of capacitance to ground between the series resistance on the RX pin and the sensor electrode.
7TVS diodeAdd a 3.3-V 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.

8Common mode inductors/magnetic beadsAdd common mode inductance and magnetic beads to the power supply as needed.
9OthersI2C communication line pullup resistorAdd 2.2-kΩ pullup resistor.
10I2C communication pins (GUI default configuration)MSP430FR25x2:

P2.4: IRQ (OPEN DRAIN)

P2.5: UCB0 I2C SDA

P2.6: UCB0 I2C SCL

MSP430FR263x, MSP430FR253x, MSP430FR267x:

P1.1: IRQ (OPEN DRAIN)

P1.2: UCB0 I2C SDA

P1.3: UCB0 I2C SCL

11UART communication pin (GUI default configuration)MSP430FR25x2:

P2.0: UCA0 UART TXD

P2.1: UCA0 UART RXD

MSP430FR263x, MSP430FR253x, MSP430FR267x:

P1.4: UCA0 UART TXD

P1.5: UCA0 UART RXD

12Boot Loader (BSL)For BSL pin definition, refer to the Bootloader chapter in the corresponding device datasheet.
13Button to MCU connectorWill increase the parasitic capacitance to the ground, it is not recommended to use.
14Test pointIncrease the related test points of VCC, GND, communication port.

During preliminary evaluation of the EMC anti-noise design, TI recommends allowing for changes to components and layout and finalizing according to the test results. An important choice is the series resistance on the CAP I/O pins. Because the series resistance affects the base capacitance and the capacitance change caused by the touch at the same time, the series resistance itself does not affect the sensitivity of the button. Because it forms a low-pass filter with parasitic capacitance, a larger series resistance can increase the noise immunity of the button. However, too large a resistance affects the charge transfer time. The charge and discharge waveforms on the CAP I/O pins are shown in Figure 4-2. This change to the charge transfer time decreases the sensitivity of the button, which is especially obvious in a self-inductive solution with a larger base capacitance of the sensor. The charge transfer period can be extended and the Frequency Divider parameter in the GUI can be modified to solve the problem.

GUID-20210517-CA0I-79KM-MWSF-JK3WJC3VGM23-low.pngFigure 4-2 Incomplete and Complete Charge Transfer Cycle (GEN2)