STM32 VCAP Pins (Hardware Connection, Capacitor Value)

In this quick guide, we’ll explain the functionality of the STM32 VCAP pins, how to decide on the needed capacitor’s value, and the hardware connections for the SM32 VCAP pins on a custom PCB design. Without further ado, let’s get right into it!

Table of Contents

1. STM32 VCAP Pins
2. STM32 VCAP Recommended Capacitor Value
3. STM32 VCAP Pins Hardware Connection
4. Wrap Up

STM32 VCAP Pins

High-performance STM32 microcontrollers typically have one or two V_CAP pins intended for connecting external bypassing capacitors to stabilize the internal LDO that generates the internal V_CORE voltage. High-speed operation of the STM32 uC’s CPU (>180MHz) will require you to enable the internal LDO and select a proper output voltage scaling (VOS) to achieve the desired F_CPU frequency.

Here is a table from the STM32H7 datasheet that shows you that the maximum CPU frequency is only achievable when VOS0 is selected which requires the internal LDO to be enabled. Therefore, it’s mandatory to have the external V_CAP capacitors in check.

The internal LDO generates a lower voltage source for the core (V_CORE) than the 3.3v standard (between 1v-1.4v) to reduce the power dissipation at higher clock frequencies. Just like what happens when overclocking a PC’s CPU, the supply voltage changes to maintain operational stability and a manageable power/heat dissipation.

STM32 VCAP Recommended Capacitor Value

In the datasheet of the target STM32 microcontroller that you’re using, you’ll find a table similar to the one shown below stating the capacitor value needed for the V_CAP pins.

STM32 VCAP Pins Hardware Connection

Typically, you’ll need a 2.2µF per V_CAP pin. It’s highly recommended to use low ESR ceramic capacitors placed as near as possible to the STM32’s V_CAP pins on the PCB. Here’s an example of the hardware connections needed for the V_CAP pins of an STM32H750 microcontroller that I’m currently using in a recent HW design project.

Wrap Up

In conclusion, we’ve explored the functionality of the VCAP pins, why external capacitors are mandatory, how to decide on the external capacitors’ value, and the hardware connections needed to get it done correctly.

If you’re just getting started with STM32, you need to check out the STM32 Getting Started Tutorial here. Follow this STM32 Series of Tutorials to learn more about STM32 Microcontrollers Programming.