Espressif Systems ESP32-S2 Hardware Design Manuallines page 12

2. Schematic Checklist
Notice:
• Please note the requirements for the 32.768 kHz crystal.
– Equivalent series resistance (ESR) ⩽ 70 kΩ.
– Load capacitance at both ends should be configured according to the crystal's specification.
• The parallel resistor R12 is used for biasing the crystal circuit (5 MΩ < R12 ⩽ 10 MΩ). In general, users do not need
to populate R12.
• If the RTC source is not required, then pin21 (XTAL_32K_P) and pin22 (XTAL_32K_N) can be used as general
D GPIOs.
Figure 8 shows the schematic of the external signal.
VDD33
VDD33
The external signal can be input to XTAL_32K_P through a DC blocking capacitor (about 20 pF). XTAL_32K_N can
be floating. The signal should meet the following requirements:
XTAL_32K_P input
C
Sine wave or square wave
VDD33
2.5 RF
C6
The impedance matching point for the RF pin (pin2) of ESP32-S2 is (34+j5) Ω. A π-type matching network is
10uF
essential for antenna matching in the circuit design. CLC structure is recommended for the matching network.
Figure 9 shows the RF matching schematic.
GND
ANT2
1
2
PCB ANT
B
The values of C11, L2 and C12
vary with the actual PCB board.
Note:
The parameters of the components in the matching network are subject to the actual antenna and PCB layout.
Espressif Systems
A
5
CLK_32K
C17 TBD
C2
100pF
Figure 8: Schematic of External Oscillator
GND
L1
C7 C8
0.1uF
1uF
GND GND
RF_ANT
L2
C11
TBD
GND GND
Figure 9: ESP32­S2 RF Matching Schematic
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The values of C1 and C4 vary with
the selection of the crystal.
The value of R4 varies with the actual
18
PCB board.
GPIO13
19
GPIO14
20
VDD3P3_RTC
GPIO15 21
XTAL_32K_P
C3
22
XTAL_32K_N
23
1uF
DAC_1
24
DAC_2
25
GND
C5
0.1uF
Amplitude (Vpp, unit: V)
0.6 < Vpp < VDD
GND
2.0nH
C9
TBD
GND
LNA_IN
TBD
C12
GPIO0
GPIO1
TBD
GPIO2
GPIO3
GPIO4
GND
GPIO5
GPIO6
GPIO7
GPIO8
GPIO9
VDD33
8 ESP32-S2 Hardware Design Guidelines V1.1
4
GND
1
VDDA
2
LNA_IN
3
VDD3P3
4
VDD3P3
5
GPIO0
6
GPIO1
7
GPIO2
8
GPIO3
9
GPIO4
10
GPIO5
11
GPIO6
12
GPIO7
13
GPIO8
14
GPIO9
U1
C15
GN
GND
C1
TBD
R4
0 40