Espressif ESP32 Technical Reference Manual page 693

31 Low-Power Management (RTC_CNTL)
31.3.5 Brownout Detector
The brownout detector checks the voltage of pin VDD3P3_RTC. If the voltage drops rapidly and becomes too
low, the detector would trigger a signal to shut down some power-consuming blocks (such as LNA, PA, etc.)
to allow extra time for the digital block to save and transfer important data. The power consumption of the
detector is ultra low. It remains enabled whenever the chip is powered on, with an adjustable trigger level
calibrated around 2.5V.
1. As the output of the brownout detector,
pin VDD3P3_RTC is lower than the threshold value.
2. RTC_CNTL_DBROWN_OUT_THRES[2:0]
around 2.5V.
Figure 31-5 shows the structure of a brownout detector.
31.3.6 RTC Module
The RTC module is designed to handle the entry into, and exit from, the low-power mode, and control the clock
sources, PLL, power switch and isolation cells to generate power-gating, clock-gating, and reset signals. As for
the low-power management, RTC is composed of the following modules (see Figure 31-6):
• RTC main state machine: records the power state.
Espressif Systems
Figure 31-4. Flash Voltage Regulator
RTC_CNTL_BROWN_OUT_DET
is used to tune the threshold voltage, which is usually calibrated
Figure 31-5. Brownout Detector
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goes high when the voltage of
ESP32 TRM (Version 5.2)