• MCU: U2
• Support Components:
  • Decoupling:
    • Place a 0.1 µF capacitor very close to every VDD pin.
    • Place additional bulk capacitors (10 µF) on the main 3.3 V rail.
  • Reset Circuit:
    • An external pull-up resistor (typically 10 kΩ) connected between the RESET pin and VDD.
    • Optionally, a small capacitor (around 100 nF) from RESET to ground for noise filtering.
  • Clocks/Crystals:
    • If using an external clock source, include the required crystal oscillator circuitry as per the Teensy 3.6 reference.
  • Bypass Networks:
    • Include local bypass capacitors (100 nF) adjacent to other critical power pins as recommended in the reference design.

• USB Power Interface:
  • USB Connector:
    • A USB Type-C or Micro-USB connector providing 5 V input.
  • Power Regulation:
    • A 5 V-to-3.3 V LDO regulator (or switching regulator) is used to supply the MCU and peripherals.
    • Filtering & Protection:
      • Input and output decoupling capacitors (e.g., 1 µF to 10 µF) and optionally ferrite beads or LC filters.
      • Overcurrent and reverse polarity protection elements (e.g., polyfuse and diode) to secure the supply.

• Socket:
  • Use a micro SD card socket.
• Connections & Support Components:

  Table

  ---

  Signal	MCU (U2) Function	SD Card Socket (SD1) Pin	Notes
  SPI Clock	SPI_SCK (from Teensy)	CLK	Direct, short trace recommended
  SPI MOSI	SPI_MOSI (from Teensy)	CMD	In SPI mode use CMD as MOSI; a 10 kΩ pull-up resistor may be added if needed
  SPI MISO	SPI_MISO (from Teensy)	DAT0	Direct, ensure trace impedance is maintained
  SPI Chip-Select	GPIO (assign an available digital)	DAT3	Connect a chosen GPIO (e.g., GPIO PIN designated in firmware)
  Power	3.3 V Supply	VDD	Bypass capacitor (typically 100 nF) placed as close to the socket pins as possible
  Ground	System Ground	VSS	Connect to the common ground plane

• Bypass:
  • Place a 100 nF capacitor between VDD and VSS of the micro SD card socket.
  • Optionally add a 10 kΩ resistor (pull-up) on the CMD line if required by your layout or noise considerations.

• USB Debug/Programmer Interface (if required):
  • Optionally include circuitry (e.g., UART level shifters) for debugging and programming the Teensy.
• Oscillator and Clock Generation:
  • If the design calls for a more accurate clock than provided by the MCU’s internal oscillator, integrate a crystal oscillator and load capacitors as per the manufacturer’s recommendations.
• Peripheral Interfaces & I/O:
  • All spare I/O pins on the Teensy can be routed to headers or test points for future expansion.
  • Include ESD protection diodes where necessary on exposed connectors.

• Signal Trace Integrity:
  • For SPI lines (CLK, MOSI, MISO, CS) keep traces as short and direct as possible.
  • Use a solid ground plane below the signal traces to minimize interference.
• Component Placement:
  • Place decoupling capacitors directly adjacent to the power pins.
  • Group power supply components (USB connector, regulator) close together and routing away from sensitive analog signals.
• Annotations & Labels:
  • Clearly label all nets (e.g., VCC3.3, GND, SPI_SCK, SPI_MOSI, SPI_MISO, SPI_CS).
  • Include reference designators for every component.

Diagram

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