TI recommends connecting a combination of a 10-µF and a 0.1-µF low-ESR ceramic decoupling capacitor across the VDD and VSS pins, as well as placing these capacitors as close as possible to the supply pins that they decouple (within a few millimeters) to achieve a minimal loop area. The 10-µF bulk decoupling capacitor is a recommended value for most applications, but this capacitance may be adjusted if needed based upon the PCB design and application requirements. For example, larger bulk capacitors can be used, but this can affect the supply rail ramp-up time.

The NRST reset pin must be pulled up to VDD (supply level) for the device to release from RESET state and start the boot process. TI recommends connecting an external 47-kΩ pullup resistor with a 10-nF pulldown capacitor for most applications, enabling the NRST pin to be controlled by another device or a debug probe.

The SYSOSC frequency correction loop (FCL) circuit utilizes an external 100-kΩ with 0.1% tolerance resistor with a temperature coefficient (TCR) of 25ppm/C or better populated between the ROSC pin and VSS. This resistor establishes a reference current to stabilize the SYSOSC frequency through a correction loop. This resistor is required if the FCL feature is used for higher accuracy, and it is not required if the SYSOSC FCL is not enabled. When the FCL mode is not used, the PA2 pin may be used as a digital input/output pin.

A 0.47-µF tank capacitor is required for the VCORE pin and must be placed close to the device with minimum distance to the device ground. Do not connect other circuits to the VCORE pin.

For the 5-V-tolerant open drain (ODIO), a pullup resistor is required to output high for I2C and UART functions, as the open drain IO only implement a low-side NMOS driver and no high-side PMOS driver. The 5V-tolerant open drain IO are fail-safe and may have a voltage present even if VDD is not supplied.

The USB circuit requires a capacitor across the VUSB and VSS pins. If VUSB sourced from VCC, recommend connecting a 0.1-µF low-ESR ceramic decoupling capacitor. If VUSB sourced from a separated power supply, recommend connecting a combination of a 1-µF and a 0.1-µF low-ESR ceramic decoupling capacitor. As well as place the capacitor as close as possible to the supply pins that they decouple (within a few millimeters) to achieve a minimal loop area.

Figure 9-1 Basic Application Schematic