Should I use an external brownout detector / supply voltage monitor with my Silicon Labs MCU?
All Silicon Labs MCUs have an internal brown out detector / supply voltage monitor. In most cases, the internal supply monitor is sufficient and an external supply monitor is not required.
However, an external supply monitor is recommended for devices where the supply monitor's reset threshold is below the minimum required supply voltage.
For example, the C8051F36x's supply voltage must be between 3.0 V and 3.6 V when SYSCLK > 50 MHz:
And the supply monitor's reset threshold is 2.55V typical:
For SYSCLK > 50 MHz and the typical case reset threshold, the MCU will be operating out of specification and unpredictably when the supply voltage is between 2.55 V and 3.0 V. Therefore, an external supply monitor should be used to reset the MCU when the supply voltage drops below 3.0 V. This guarantees that MCU operation is within specification and predictable at all times.