Notepad of a tinker, maker, hacker or whatever you call it :)

Designing an STM32L15xx board

Following are some notes about ST application notes I read to design an STM32L151 board.
All documents can be found here.

AN2606 - Microcontroller system memory boot mode

AN2606 - Microcontroller system memory boot mode

  • Bootloader in USART1 or USART2
  • Unused RX (USART1 or 2) pin must be pulled and not left floating

AN3216 - Hardware development

AN3216 - Getting started with STM32L1xxx hardware development


  • Voltage range
  • Full speed (Range 1) : 2.0 to 3.6 VDC
  • Capacitors:
  • 1x100 nF by VDD pin
  • Min 4.7µf for the chip, 10µF recommended
  • Reset and power supply supervisor
  • Power on/down-reset signal - No consumption
  • Programmable voltage detector - No consumption - between 1.85 and 3.02 V, 200 mV steps. Generates an interrupt.
  • Brownout detector - Slight power consumption, can be disabled by option byte
  • Reset circuit
  • A 100 nF grounded capacitor is recommended, can be reduced to 10 nF
  • Clock
  • Multi-Speed Internal : Activated on reset, can be trimmed with high speed external clock.
  • High Speed External clock : Optional, can be clock source (<32 MHz) or oscillator (1 to 24 MHz)
  • Low Speed External lock : Optional, can be clock source or oscillator (32.768 kHz). [-30%; +60%} tolerances
  • PLL : Hook to generate various internal clocks
  • Clock Security System : Disable HSE if failure detected
  • Boot configuration : boot0 and boot1 inputs triggers 3 modes:
  • x0 : Flash memory
  • 01 : System memory (ST bootloader)
  • 11 : SRAM memory
  • Inline 10 k resistor is recommended
  • ST bootloader via USART1 or USART2
  • RX pin from unused USART must not be left floating


  • Interface : ARM JTAG (5 pins) or SW ( SerialWire - 2 pins)
  • See page 23


  • Use 4 layers PCB with dedicated VSS and VDD layerS. If not, ensured good ground
  • Separate usages (High current, analog...)
  • Avoid floating pin I/O, disable unused features

AN1709 - EMC Design (hardware)

EMC design guide for ST microcontrollers

  • External oscillators must be as close as possible to the µC
  • Avoid tracks surface and inductance
    • Multiple via reduce inductance
  • Power supply must be decoupled
  • Unused I/O pin must be set to low output
  • Shielding might improve, but depends on selected material

AN1015 - EMC Design (software)

Software techniques for improving microcontrollers EMC performance