Hello,
I would like to power an STM32WLE5 with two voltage levels:
- VBAT: 2 series AA batteries, yielding a voltage comprised between (~3.2V and ~2V) over the life of the batteries.
- VBOOST: A boosted voltage from the batteries with a target of 3V. If the batteries are old enough, the voltage is boosted to 3V. If they are brand new, the automatic passt-hrough connects VBAT directly. Thus, VBOOST = [3, ~3.2] volts
Are there requirements on VDD that prevents the MCU from operating normally if the voltage changes? What would be the maximum rate of change? In section 5.3.4 of the datasheet, min VDD fall time rate is specified to 10µs/V. My understanding is that VDD should not drop more than 0.1V/µs to operate normally. Is that right?
Are there other requirements that I may have missed?
Some context
The system features a white LED matrix display and a stepper motor. When the stepper is switched on, it draws enough current that the voltage drops. If the batteries have some age (but not depleted), the drop is large enough that the voltage can fall under the BOR threshold.
For the LED to emit a constant amount of light, we need a voltage supply of 3V, which is not possible when the stepper is on.
For these reasons, I want to use a boost converter with a bypass mode. Most of the time, the boost would be bypassed and the MCU would operate directly with what's available from the batteries [~2V, ~3.2V]. When the system activates the LEDs or the stepper, it first enables the boost. This prevents the MCU from resetting in case the voltage drops too low, and allows the LED matrix to light up consistently.
Thank you
