Rtc (Optional); Adc; Esp32 Crystal Oscillator (Rtc) - Espressif Systems ESP32 Hardware Design Manuallines

2. SCHEMATIC CHECKLIST AND PCB LAYOUT DESIGN

2.1.4.2 RTC (Optional)

ESP32 supports an external 32.768 kHz crystal oscillator to act as the RTC sleep clock.
Notice:
If the RTC source is not required, then Pin12 32K_XP and Pin13 32K_XN can be used as GPIOs.
2.1.5 RF
The output impedance of the RF pins of ESP32 (QFN 6*6) and ESP32 (QFN 5*5) are (30+j10) and (35+j10) Ω
respectively. A π-type matching network is essential for antenna matching in the circuit design. CLC structure is
recommended for the matching network.
ANT1
1
2
PCB ANT
GND
Note:
The parameters of the components in the matching network are subject to the actual antenna and PCB layout.

2.1.6 ADC

It is recommended that users add a 0.1 µF filter capacitor to a pad when using the ADC function.
• Pins SENSOR_VP or SENSOR_VN will trigger an input glitch lasting for 80 ns once the temperature sensor,
or SARADC1, or SARADC2, or Hall sensor is initialized.
• It is recommended that users avoid using SENSOR_VP or SENSOR_VN as input GPIO when designing the
Espressif Systems
C22 12pF
U4
32kHz
C23 12pF
Figure 6: ESP32 Crystal Oscillator (RTC)
L4 2.7nH
C15 C14
2.0pF 2.7pF 270pF
GND
GND
Figure 7: ESP32 RF Matching Schematics
GPIO35 11
VDET_2
GPIO32 12
32K_XP
13
GPIO33
32K_XN
GPIO25 14
GPIO25
U2
C16
SENSOR_VP
SENSOR_VN
C17
CHIP_PU
12 ESP32 Hardware Design Guidelines V2.1
1
VDDA
2
LNA_IN
3
VDD3P3
4
VDD3P3
5
SENSOR_VP
6
SENSOR_CAPP
7
SENSOR_CAPN
8
SENSOR_VN
9