Datasheet

3 Functional Description
3.2 System Clocks
3.2.1 CPU Clock
The CPU clock has three possible sources:
• external main crystal clock
• fast RC oscillator (typically about 17.5 MHz, and adjustable)
• PLL clock
The application can select the clock source from the three clocks above. The selected clock source drives the
CPU clock directly, or after division, depending on the application. Once the CPU is reset, the default clock
source would be the external main crystal clock divided by 2.
Note:
ESP32-C3 is unable to operate without an external main crystal clock.
3.2.2 RTC Clock
The RTC slow clock is used for RTC counter, RTC watchdog and low-power controller. It has three possible
sources:
• external low-speed (32 kHz) crystal clock
• internal slow RC oscillator (typically about 136 kHz, and adjustable)
• internal fast RC oscillator divided clock (derived from the fast RC oscillator divided by 256)
The RTC fast clock is used for RTC peripherals and sensor controllers. It has two possible sources:
• external main crystal clock divided by 2
• internal fast RC oscillator divide-by-N clock (typically about 17.5 MHz, and adjustable)
3.3 Analog Peripherals
3.3.1 AnalogtoDigital Converter (ADC)
ESP32-C3 integrates two 12-bit SAR ADCs.
• ADC1 supports measurements on 5 channels, and is factory-calibrated.
• ADC2 supports measurements on 1 channel, and is not factory-calibrated.
For ADC characteristics, please refer to Table 15.
3.3.2 Temperature Sensor
The temperature sensor generates a voltage that varies with temperature. The voltage is internally converted via
an ADC into a digital value.
The temperature sensor has a range of –40 °C to 125 °C. It is designed primarily to sense the temperature
changes inside the chip. The temperature value depends on factors like microcontroller clock frequency or I/O
load. Generally, the chip’s internal temperature is higher than the operating ambient temperature.
Espressif Systems 19
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ESP32-C3 Series Datasheet v1.2