Espressif Systems ESP32-C3 Series Instruction Manual

ESP32C3 Family
Hardware Design Guidelines
Prerelease version 0.5
Espressif Systems
Copyright © 2021
www.espressif.com

About This Document
The guidelines outline recommended design practices when developing standalone or add-on systems based on
the ESP32-C3 series of products, including ESP32-C3 SoCs, ESP32-C3 modules and ESP32-C3 development
boards.
Document Updates
Please always refer to the latest version on https://www.espressif.com/en/support/download/documents.
Revision History
For the revision history of this document, please refer to the last page.
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Contents
Contents
1 Overview 4
2 Schematic Checklist 5
2.1 Power Supply 6
2.1.1 Digital Power Supply 6
2.1.2 Analog Power Supply 6
2.2 Power-on Sequence and System Reset 7
2.2.1 Power-on Sequence 7
2.2.2 Reset 8
2.3 Flash 8
2.4 Clock Source 9
2.4.1 External Clock Source (compulsory) 9
2.4.2 RTC Clock (optional) 10
2.5 RF 11
2.6 UART 11
2.7 ADC 11
2.8 Strapping Pins 11
2.9 GPIO 13
3 PCB Layout Design 16
3.1 General Principles of PCB Layout 16
3.2 Placement of Module on the Base Board 16
3.3 Power Supply 19
3.4 Crystal 20
3.5 RF 21
3.6 Flash 23
3.7 UART 23
3.8 Typical Layout Problems and Solutions 24
3.8.1 Ripple in the power supply is not large, but the RF transmit (TX) performance is rather poor. 24
3.8.2 Ripple in power supply is small during packet transmission, but RF TX performance is still poor. 24
3.8.3 When ESP32-C3 family transmits data packets, the measured power is much higher or lower
than the target power, and the EVM is relatively poor. 24
3.8.4 TX performance is not bad, but the RX sensitivity is low. 24
4 Hardware Development 26
4.1 ESP32-C3-WROOM-1 Module 26
4.2 ESP32-C3 family Development Boards 26
Revision History 27
Solutions, Documentation and Legal Information 28
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List of Figures
List of Figures
1 ESP32-C3 Family Schematic 5
2 ESP32-C3 Family Digital Power Supply Pins 6
3 ESP32-C3 Family Analog Power Supply Pins 7
4 ESP32-C3 Family Power-up and Reset Timing 8
5 ESP32-C3 Family Flash Circuit 9
6 Schematic for ESP32-C3 Family’s Crystal 9
7 Schematic for ESP32-C3 Family’s Oscillator 10
8 Schematic for ESP32-C3 Family’s External Crystal (RTC) 10
9 ESP32-C3 Family RF Matching Schematic 11
10 Setup and Hold Times for the Strapping Pin 13
11 ESP32-C3 Family PCB Layout 16
12 Placement of ESP32-C3 Modules on Base Board. Antenna Feed Point on the Right 17
13 Placement of ESP32-C3 Modules on Base Board. Antenna Feed Point on the Left 17
14 Keepout Zone for ESP32-C3 Module’s Antenna on the Base Board 18
15 ESP32-C3 Family Power Traces in a Four-layer PCB Design 19
16 ESP32-C3 Family Stub in a Four-layer PCB Design 19
17 ESP32-C3 Family Crystal Layout 21
18 ESP32-C3 Family RF Layout in a Four-layer PCB Design 21
19 ESP32-C3 RF Stub in a Four-layer PCB Design 22
20 ESP32-C3 Family PCB Stack-up Design 23
21 ESP32-C3 Family Flash Layout 23
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1 Overview
1. Overview
ESP32-C3 family is an ultra-low-power MCU-based SoC solution that supports 2.4 GHz Wi-Fi and Bluetooth®
Low Energy (Bluetooth LE). With its state-of-the-art power and RF performance, this SoC is an ideal choice for a
wide variety of application scenarios relating to Internet of Things (IoT), smart home, industrial automation, health
care, and consumer electronics.
At the core of this chip is a 32-bit RISC-V single-core processor that operates at up to 160 MHz. The chip
supports application development, without the need for a host MCU.
ESP32-C3 family provides a highly-integrated way to implement Wi-Fi and Bluetooth LE technologies using a
complete RF subsystem, including a antenna switch, RF balun, power amplifier, low noise amplifier (LNA), filter,
power management unit, calibration circuits, etc. As a result, PCB size has been greatly reduced.
With its advanced calibration circuitry, ESP32-C3 can dynamically adjust itself to remove external circuit
imperfections or adapt to changes in external conditions. As such, the mass production of ESP32-C3 family
does not require expensive and specialized Wi-Fi test equipment.
For more information about ESP32-C3 family, please refer to ESP32-C3 Family Datasheet.
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2 Schematic Checklist
2. Schematic Checklist
Thanks to high integration, ESP32-C3 family has simpler peripheral circuit design.The core circuit requires about
20 resistors, capacitors and inductors in total, as well as 1 crystal and 1 SPI flash. This document explains in
detail the schematics and PCB layout of ESP32-C3 family.
Figure 1shows the core circuit of ESP32-C3 family.
5 4 3 2 1
D D
C C
The values of C1 and C2 vary with
the selection of the crystal.
The value of R1 varies with the actual
PCB board.
GPIO19
U0RXD
GPIO18
LNA_IN
GPIO0
GPIO1
SPICS0
SPID
SPIQ
SPICLK
SPIWP
SPIHDGPIO2
RF_ANT
U0TXD
SPICS0 SPID
GND
VDD33
GNDGND GND
GND GND
VDD33
VDD_SPI
GND
GND
GND GND
C1
TBD
C9
TBD
/CS
1
DI
5
VCC
8
R4 0
R7 0
R6 0
R1 0
ANT1
PCB_ANT
1
2
R5 0
C3
1uF
R2 499
R3 0
L1 2.0nH
C2
TBD
C8
TBD
C6
0.1uF
L2 TBD
C5
10uF
C4
10nF
C7
0.1uF
LNA_IN
1
VDD3P3
2
VDD3P3
3
XTAL_32K_P
4
XTAL_32K_N
5
6 19
SPIWP
20
SPICS0 21
SPICLK 22
SPID 23
SPIQ 24
U0RXD 27
U0TXD 28
XTAL_N 29
XTAL_P 30
GND 33
VDDA 32 VDDA 31
GPIO19 26 GPIO18 25
U1
40MHz(±10ppm)
XIN
1
GND
2XOUT 3
GND 4
5 4 3 2 1
B B
A A
The values of C8, L2 and C9
vary with the actual PCB board.
If using ESP32-C3FN4 or ESP32-C3FH4,
external flash could be removed.
CHIP_EN
GPIO4
GPIO5
GPIO6
GPIO7
GPIO8
GPIO9
GPIO10
SPIHDGPIO2
GPIO3
SPICLK
SPIHD SPIWP
SPIQ
XTAL_P
GND
GNDGND
GND GNDGND
VDD33
VDD_SPI
VDD33
GND
GND
VDD33
GND
VDD33
L3 TBD
U3 FLASH-3V3
/CS
DO 2
/WP 3
GND
4
DI
CLK
6
/HOLD
7
VCC
R7 0
C12
0.1uF
C10
0.1uF
R1 0
C1
10nF
Y1
40MHz(±10ppm)
VCC
4
NC
1GND 2
OUT 3
R8
10K
C11
1uF
U2 ESP32-C3
XTAL_32K_N
GPIO2
6
CHIP_EN
7
MTMS
9
MTDI
10
VDD3P3_RTC
11
MTCK
12
MTDO
13
GPIO8
14
GPIO9
15
GPIO10
16
VDD3P3_CPU 17
VDD_SPI 18
SPIHD
19
SPIWP
GPIO3
8
Figure 1: ESP32C3 Family Schematic
Highlights in ESP32-C3 family circuit design may be broken down into nine major sections:
• Power supply
• Power-on sequence and system reset
• Flash
• Clock source
• RF
• UART
• ADC
• Strapping pins
• GPIO
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2 Schematic Checklist
2.1 Power Supply
For details of using power supply pins, please refer to Section Power Scheme in
ESP32-C3 Family Datasheet.
2.1.1 Digital Power Supply
Pin 11 and pin 17 are the power supply pins for RTC IO and CPU IO respectively, in a voltage range of 3.0 V ~
3.6 V. We recommend adding 0.1 µF capacitors close to each digital power supply pin.
When working as an output power supply pin, VDD_SPI can be powered by VDD3P3_CPU via RSP I (nominal 3.3
V). Therefore, there will be a voltage drop on VDD_SPI to VDD3P3_CPU. We recommend adding a 1 µF filter
capacitor between VDD_SPI and ground.
When not working as a power supply pin, VDD_SPI can be used as GPIO11.
5
5
4
4
3
3
2
2
1
1
D
D
C
C
B
B
A
A
NC: No component.
The values of C8, L2 and C9
vary with the a tual PCB board.
The values of C1 and C2 vary with
the sele tion of the rystal.
The value of R1 varies with the a tual
PCB board.
GPIO19
CHIP_EN
GPIO4
GPIO5
GPIO6
GPIO7
GPIO8
U0RXD
GPIO18
LNA_IN
GPIO9
GPIO10
GPIO0
GPIO1
SPICS0
SPID
SPIQ
SPICLK
SPIWP
SPIHDGPIO2
GPIO3
RF_ANT
U0TXD
SPICLK
SPICS0
SPIHD SPIWP
SPID
SPIQ
GND
VDD33
GND
GND
GNDGND GND
GND GND
GND
VDD33
GND GNDGND
VDD33
VDD_SPI
VDD33
GND
VDD_SPI
GND
GND
GND GND
C1
TBD
C9
TBD
U3 FLASH-3V3
/CS
1
DO 2
/WP 3
GND
4
DI 5
CLK
6
/HOLD
7
VCC 8
R4 0
R7 0
R6 0
C12
0.1uF
R1 0
ANT1
PCB_ANT
1
2
R5 0
C10
0.1uF
C3
1uF
R2 499
R3 0
L1 2.0nH
C2
TBD
C8
TBD
C6
0.1uF
L2 TBD
C5
10uF
C4
100pF
C7
0.1uF
C11
1uF
U2 ESP32-C3
LNA_IN
1
VDD3P3
2
VDD3P3
3
XTAL_32K_P
4
XTAL_32K_N
5
GPIO2
6
CHIP_EN
7
MTMS
9
MTDI
10
VDD3P3_RTC
11
MTCK
12
MTDO
13
GPIO8
14
GPIO9
15
GPIO10
16
VDD3P3_CPU 17
VDD_SPI 18
SPIHD 19
SPIWP 20
SPICS0 21
SPICLK 22
SPID 23
SPIQ 24
U0RXD 27
U0TXD 28
XTAL_N 29
XTAL_P 30
GND 33
GPIO3
8
VDDA 32 VDDA 31
GPIO19 26 GPIO18 25
U1
40MHz(±10ppm)
XIN
1
GND
2XOUT 3
GND 4
R8
10K
Figure 2: ESP32C3 Family Digital Power Supply Pins
Notice:
When VDD_SPI works as the power supply pin for embedded and external 3.3 V flash, VDD3P3_CPU should
be 3.0 V or above, so as to fall into flash’s operating voltage range.
2.1.2 Analog Power Supply
Pin 2, pin 3, pin 31, and pin 32 are the analog power supply pins, working at 3.0 V ~3.6 V. Please note that when
ESP32-C3 family works in transmission (TX) mode, the instantaneous current is higher and may cause a power
rail collapse. Therefore, it is highly recommended to add a 10 µF capacitor to the power trace, which can work in
conjunction with the 0.1 µF capacitor. In addition, a LC filter circuit needs to be added near pin 2 and pin 3 to
suppress high-frequency harmonics. The inductor’s rated current is preferably 500 mA or above. Refer to Figure
3and place the appropriate decoupling capacitor near each analog power pin.
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2 Schematic Checklist
5 4 3 2 1
D D
C C
The values of C1 and C2 vary with
the selection of the crystal.
The value of R1 varies with the actual
PCB board.
GPIO19
U0RXD
GPIO18
LNA_IN
GPIO0
GPIO1
SPICS0
SPID
SPIQ
SPICLK
SPIWP
SPIHDGPIO2
RF_ANT
U0TXD
SPICS0 SPID
GND
VDD33
GNDGND GND
GND GND
VDD33
VDD_SPI
GND
GND
GND GND
C1
TBD
C9
TBD
/CS
1
DI
5
VCC
8
R4 0
R7 0
R6 0
R1 0
ANT1
PCB_ANT
1
2
R5 0
C3
1uF
R2 499
R3 0
L1 2.0nH
C2
TBD
C8
TBD
C6
0.1uF
L2 TBD
C5
10uF
C4
10nF
C7
0.1uF
LNA_IN
1
VDD3P3
2
VDD3P3
3
XTAL_32K_P
4
XTAL_32K_N
5
6 19
SPIWP
20
SPICS0 21
SPICLK 22
SPID 23
SPIQ 24
U0RXD 27
U0TXD 28
XTAL_N 29
XTAL_P 30
GND 33
VDDA 32 VDDA 31
GPIO19 26 GPIO18 25
U1
40MHz(±10ppm)
XIN
1
GND
2XOUT 3
GND 4
5 4 3 2 1
B B
A A
The values of C8, L2 and C9
vary with the actual PCB board.
If using ESP32-C3FN4 or ESP32-C3FH4,
external flash could be removed.
CHIP_EN
GPIO4
GPIO5
GPIO6
GPIO7
GPIO8
GPIO9
GPIO10
SPIHDGPIO2
GPIO3
SPICLK
SPIHD SPIWP
SPIQ
XTAL_P
GND
GNDGND
GND GNDGND
VDD33
VDD_SPI
VDD33
GND
GND
VDD33
GND
VDD33
L3 TBD
U3 FLASH-3V3
/CS
DO 2
/WP 3
GND
4
DI
CLK
6
/HOLD
7
VCC
R7 0
C12
0.1uF
C10
0.1uF
R1 0
C1
10nF
Y1
40MHz(±10ppm)
VCC
4
NC
1GND 2
OUT 3
R8
10K
C11
1uF
U2 ESP32-C3
XTAL_32K_N
GPIO2
6
CHIP_EN
7
MTMS
9
MTDI
10
VDD3P3_RTC
11
MTCK
12
MTDO
13
GPIO8
14
GPIO9
15
GPIO10
16
VDD3P3_CPU 17
VDD_SPI 18
SPIHD
19
SPIWP
GPIO3
8
Figure 3: ESP32C3 Family Analog Power Supply Pins
Notice:
• If you use a single power supply, the recommended voltage of the power supply for ESP32-C3 family
is 3.3 V, and its recommended output current is 500 mA or more.
• You are suggested to add an ESD protection diode at the power entrance.
2.2 Poweron Sequence and System Reset
2.2.1 Poweron Sequence
ESP32-C3 family uses a 3.3 V system power supply. The chip should be activated after the power rails have
stabilized. This is achieved by delaying the activation of pin 7 CHIP_EN after the 3.3 V rails have been brought
up.
Figure 4shows the power-up and reset timing of ESP32-C3 family. Details about the parameters are listed in
Table 1.
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2 Schematic Checklist
VDDA,
VDD3P3,
VDD3P3_RTC,
VDD3P3_CPU
CHIP_PU
t0t1
VIL_nRST
2.8 V
Figure 4: ESP32C3 Family Powerup and Reset Timing
Table 1: Description of ESP32C3 Family Powerup and Reset Timing Parameters
Min
Parameter Description (µs)
t0
Time between bringing up the VDDA, VDD3P3, VDD3P3_RTC, and
VDD3P3_CPU rails, and activating CHIP_PU 50
t1Duration of CHIP_PU signal level < VIL_nRST to reset the chip 50
Notice:
To ensure the power supply to the ESP32-C3 family chip is stable during power-up, it is advised to add an
RC delay circuit at the CHIP_EN pin. The recommended setting for the RC delay circuit is usually R = 10 kΩ
and C = 1 µF. However, specific parameters should be adjusted based on the power-up timing of the power
supply and the power-up and reset sequence timing of the chip.
2.2.2 Reset
CHIP_EN can be used as the reset pin of ESP32-C3 family. When CHIP_EN is at low level, the reset voltage
(VIL_nRST ) should be (–0.3 ~0.25 × VDD) V (where VDD is the I/O voltage for a particular power domain of pins).
To avoid reboots caused by external interference, route the CHIP_EN trace as short as possible, and add a
pull-up resistor as well as a capacitor to ground whenever possible.
Notice:
CHIP_EN pin must not be left floating.
2.3 Flash
ESP32-C3 family can support up to 16 MB external flash. The ESP32-C3-WROOM-1 module uses a 4 MB SPI
flash, powered by VDD_SPI. We recommend reserving a serial resistor (initially of 0 Ω) on the SPI line, to lower the
driving current, adjust timing, reduce crosstalk and external interference, etc.
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2 Schematic Checklist
5
5
4
4
3
3
2
2
1
1
D D
C C
B B
A A
NC: No component.
The values of C8, L2 and C9
vary with the actual PCB board.
The values of C1 and C2 vary with
the selection of the crystal.
The value of R1 varies with the actual
PCB board.
If using ESP32-C3FN4 or ESP32-C3FH4,
flash is not mounted.
GPIO19
CHIP_EN
GPIO4
GPIO5
GPIO6
GPIO7
GPIO8
U0RXD
GPIO18
LNA_IN
GPIO9
GPIO10
GPIO0
GPIO1
SPICS0
SPID
SPIQ
SPICLK
SPIWP
SPIHDGPIO2
GPIO3
RF_ANT
U0TXD
SPICLK
SPICS0
SPIHD SPIWP
SPID
SPIQ
XTAL_P
GND
VDD33
GND
GND
GNDGND GND
GND GND
GND
VDD33
GND GNDGND
VDD33
VDD_SPI
VDD33
GND
VDD_SPI
GND
GND
GND GND
GND
VDD33
GND
C1
TBD
C9
TBD
L3 TBD
U3 FLASH-3V3
/CS
1
DO 2
/WP 3
GND
4
DI 5
CLK
6
/HOLD
7
VCC 8
R4 0
R7 0
R6 0
C12
0.1uF
R1 0
ANT1
PCB_ANT
1
2
R5 0
C10
0.1uF
C3
1uF
R2 499
R3 0
R1 0
L1 2.0nH
C2
TBD
C8
TBD
C1
10nF
Y1
40MHz(±10ppm)
VCC
4
NC
1GND 2
OUT 3
C6
0.1uF
L2 TBD
C5
10uF
C4
10nF
C7
0.1uF
C11
1uF
U2 ESP32-C3
LNA_IN
1
VDD3P3
2
VDD3P3
3
XTAL_32K_P
4
XTAL_32K_N
5
GPIO2
6
CHIP_EN
7
MTMS
9
MTDI
10
VDD3P3_RTC
11
MTCK
12
MTDO
13
GPIO8
14
GPIO9
15
GPIO10
16
VDD3P3_CPU 17
VDD_SPI 18
SPIHD 19
SPIWP 20
SPICS0 21
SPICLK 22
SPID 23
SPIQ 24
U0RXD 27
U0TXD 28
XTAL_N 29
XTAL_P 30
GND 33
GPIO3
8
VDDA 32 VDDA 31
GPIO19 26 GPIO18 25
U1
40MHz(±10ppm)
XIN
1
GND
2XOUT 3
GND 4
Figure 5: ESP32C3 Family Flash Circuit
2.4 Clock Source
There are two clock sources for ESP32-C3 family, namely an external crystal clock source and an RTC clock
source.
2.4.1 External Clock Source (compulsory)
Currently, the ESP32-C3 family firmware only supports 40 MHz crystal. The specific capacitance of C1 and C2
depends on further testing of, and adjustment to, the overall performance of the whole circuit. We recommend
reserving a series resistor (initially of 0 Ω) on the XTAL_P clock trace to reduce the drive capability of the crystal,
as well as to minimize the impact of crystal harmonics on RF performance. Note that the accuracy of the
selected crystal needs to be ±10 ppm.
5 4 3 2 1
D D
C C
The values of C1 and C2 vary with
the selection of the crystal.
The value of R1 varies with the actual
PCB board.
GPIO19
U0RXD
GPIO18
LNA_IN
GPIO0
GPIO1
SPICS0
SPID
SPIQ
SPICLK
SPIWP
SPIHDGPIO2
RF_ANT
U0TXD
SPICS0 SPID
GND
VDD33
GNDGND GND
GND GND
VDD33
VDD_SPI
GND
GND
GND GND
C1
TBD
C9
TBD
/CS
1
DI
5
VCC
8
R4 0
R7 0
R6 0
R1 0
ANT1
PCB_ANT
1
2
R5 0
C3
1uF
R2 499
R3 0
L1 2.0nH
C2
TBD
C8
TBD
C6
0.1uF
L2 TBD
C5
10uF
C4
10nF
C7
0.1uF
LNA_IN
1
VDD3P3
2
VDD3P3
3
XTAL_32K_P
4
XTAL_32K_N
5
6 19
SPIWP
20
SPICS0 21
SPICLK 22
SPID 23
SPIQ 24
U0RXD 27
U0TXD 28
XTAL_N 29
XTAL_P 30
GND 33
VDDA 32 VDDA 31
GPIO19 26 GPIO18 25
U1
40MHz(±10ppm)
XIN
1
GND
2XOUT 3
GND 4
5 4 3 2 1
B B
A A
The values of C8, L2 and C9
vary with the actual PCB board.
If using ESP32-C3FN4 or ESP32-C3FH4,
external flash could be removed.
CHIP_EN
GPIO4
GPIO5
GPIO6
GPIO7
GPIO8
GPIO9
GPIO10
SPIHDGPIO2
GPIO3
SPICLK
SPIHD SPIWP
SPIQ
XTAL_P
GND
GNDGND
GND GNDGND
VDD33
VDD_SPI
VDD33
GND
GND
VDD33
GND
VDD33
L3 TBD
U3 FLASH-3V3
/CS
DO 2
/WP 3
GND
4
DI
CLK
6
/HOLD
7
VCC
R7 0
C12
0.1uF
C10
0.1uF
R1 0
C1
10nF
Y1
40MHz(±10ppm)
VCC
4
NC
1GND 2
OUT 3
R8
10K
C11
1uF
U2 ESP32-C3
XTAL_32K_N
GPIO2
6
CHIP_EN
7
MTMS
9
MTDI
10
VDD3P3_RTC
11
MTCK
12
MTDO
13
GPIO8
14
GPIO9
15
GPIO10
16
VDD3P3_CPU 17
VDD_SPI 18
SPIHD
19
SPIWP
GPIO3
8
Figure 6: Schematic for ESP32C3 Family’s Crystal
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5
5
4
4
3
3
2
2
1
1
D D
C C
B B
A A
NC: No component.
The values of C8, L2 and C9
vary with the actual PCB board.
The values of C1 and C2 vary with
the selection of the crystal.
The value of R1 varies with the actual
PCB board.
If using ESP32-C3FN4 or ESP32-C3FH4,
flash is not mounted.
GPIO19
CHIP_EN
GPIO4
GPIO5
GPIO6
GPIO7
GPIO8
U0RXD
GPIO18
LNA_IN
GPIO9
GPIO10
GPIO0
GPIO1
SPICS0
SPID
SPIQ
SPICLK
SPIWP
SPIHDGPIO2
GPIO3
RF_ANT
U0TXD
SPICLK
SPICS0
SPIHD SPIWP
SPID
SPIQ
XTAL_P
GND
VDD33
GND
GND
GNDGND GND
GND GND
GND
VDD33
GND GNDGND
VDD33
VDD_SPI
VDD33
GND
VDD_SPI
GND
GND
GND GND
GND
VDD33
GND
C1
TBD
C9
TBD
R4 0
U3 FLASH-3V3
/CS
1
DO 2
/WP 3
GND
4
DI 5
CLK
6
/HOLD
7
VCC 8
L3 TBD
R7 0
R6 0
ANT1
PCB_ANT
1
2
R1 0
C12
0.1uF
C3
1uF
C10
0.1uF
R5 0
R1 0
R3 0
R2 499
C1
10nF
C8
TBD
C2
TBD
L1 2.0nH
C6
0.1uF
Y1
40MHz(±10ppm)
VCC
4
NC
1GND 2
OUT 3
C5
10uF
L2 TBD
C7
1uF
C4
10nF
U2 ESP32-C3
LNA_IN
1
VDD3P3
2
VDD3P3
3
XTAL_32K_P
4
XTAL_32K_N
5
GPIO2
6
CHIP_EN
7
MTMS
9
MTDI
10
VDD3P3_RTC
11
MTCK
12
MTDO
13
GPIO8
14
GPIO9
15
GPIO10
16
VDD3P3_CPU 17
VDD_SPI 18
SPIHD 19
SPIWP 20
SPICS0 21
SPICLK 22
SPID 23
SPIQ 24
U0RXD 27
U0TXD 28
XTAL_N 29
XTAL_P 30
GND 33
GPIO3
8
VDDA 32 VDDA 31
GPIO19 26 GPIO18 25
C11
1uF
R8
10K
U1
40MHz(±10ppm)
XIN
1
GND
2XOUT 3
GND 4
Figure 7: Schematic for ESP32C3 Family’s Oscillator
Notice:
• If you use an oscillator, its output should be connected to XTAL_P on the chip through a series inductor
(initially of 20 nH). XTAL_N can be floating. Please make sure that the oscillator output is stable and
its accuracy is within ±10 ppm. It is also recommended that the circuit design for the oscillator is
compatible with the use of crystal, in case that if there is a problem with oscillator circuit, the oscillator
can be replaced by the crystal.
• Although ESP32-C3 family has calibration circuits, defects in the crystal itself (for example, large fre-
quency deviation of more than ±10 ppm, unstable performance over operating temperature range, etc)
may lead to the malfunction of ESP32-C3 family, resulting in RF performance degradation.
2.4.2 RTC Clock (optional)
ESP32-C3 family supports an external 32.768 kHz crystal to act as the RTC sleep clock.
Figure 8shows the schematic for the external 32.768 kHz crystal.
Figure 8: Schematic for ESP32C3 Family’s External Crystal (RTC)
Notice:
• 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 R10 is used for biasing the crystal circuit (5 MΩ< R12 ⩽10 MΩ). In general, you
do not need to populate R10.
• If the RTC source is not required, then pin 4 (XTAL_32K_P) and pin 5 (XTAL_32K_N) can be used as
general GPIOs.
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2.5 RF
In your circuit design, please add a π-matching network for antenna matching, preferably a CLC network.
5
5
4
4
3
3
2
2
1
1
D
D
C
C
B
B
A
A
NC: No component.
The values of C8, L2 and C9
vary with the a tual PCB board.
The values of C1 and C2 vary with
the sele tion of the rystal.
The value of R1 varies with the a tual
PCB board.
GPIO19
CHIP_EN
GPIO4
GPIO5
GPIO6
GPIO7
GPIO8
U0RXD
GPIO18
LNA_IN
GPIO9
GPIO10
GPIO0
GPIO1
SPICS0
SPID
SPIQ
SPICLK
SPIWP
SPIHDGPIO2
GPIO3
RF_ANT
U0TXD
SPICLK
SPICS0
SPIHD SPIWP
SPID
SPIQ
GND
VDD33
GND
GND
GNDGND GND
GND GND
GND
VDD33
GND GNDGND
VDD33
VDD_SPI
VDD33
GND
VDD_SPI
GND
GND
GND GND
C1
TBD
C9
TBD
U3 FLASH-3V3
/CS
1
DO 2
/WP 3
GND
4
DI 5
CLK
6
/HOLD
7
VCC 8
R4 0
R7 0
R6 0
C12
0.1uF
R1 0
ANT1
PCB_ANT
1
2
R5 0
C10
0.1uF
C3
1uF
R2 499
R3 0
L1 2.0nH
C2
TBD
C8
TBD
C6
0.1uF
L2 TBD
C5
10uF
C4
100pF
C7
0.1uF
C11
1uF
U2 ESP32-C3
LNA_IN
1
VDD3P3
2
VDD3P3
3
XTAL_32K_P
4
XTAL_32K_N
5
GPIO2
6
CHIP_EN
7
MTMS
9
MTDI
10
VDD3P3_RTC
11
MTCK
12
MTDO
13
GPIO8
14
GPIO9
15
GPIO10
16
VDD3P3_CPU 17
VDD_SPI 18
SPIHD 19
SPIWP 20
SPICS0 21
SPICLK 22
SPID 23
SPIQ 24
U0RXD 27
U0TXD 28
XTAL_N 29
XTAL_P 30
GND 33
GPIO3
8
VDDA 32 VDDA 31
GPIO19 26 GPIO18 25
U1
40MHz(±10ppm)
XIN
1
GND
2XOUT 3
GND 4
R8
10K
Figure 9: ESP32C3 Family RF Matching Schematic
Note:
The parameters of the components in the matching network are subject to the actual antenna and PCB layout.
2.6 UART
You need to connect a 499 Ωresistor to the U0TXD line to suppress the 80 MHz harmonics.
2.7 ADC
It is recommended to add a 0.1 µF filter capacitor between pins and ground when using the ADC function. ADC1
is more preferable.
2.8 Strapping Pins
Note:
The content below is excerpted from Section Strapping Pins in ESP32-C3 Family Datasheet.
ESP32-C3 family has three strapping pins:
• GPIO2
• GPIO8
• GPIO9
• GPIO10
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Software can read the values of GPIO2, GPIO8 and GPIO10 from GPIO_STRAPPING field in GPIO_STRAP_REG
register. For register description, please refer to Section GPIO Matrix Register Summary in
ESP32-C3 Technical Reference Manual.
During the chip’s system reset, the latches of the strapping pins sample the voltage level as strapping bits of ”0”
or ”1”, and hold these bits until the chip is powered down or shut down.
Types of system reset include:
• power-on-reset
• RTC watchdog reset
• brownout reset
• analog super watchdog reset
• crystal clock glitch detection reset
By default, GPIO9 is connected to the internal pull-up resistors. If GPIO9 is not connected or connected to an
external high-impedance circuit, the internal weak pull-up/pull-down will determine its default input level.
To change the strapping bit values, you can apply the external pull-down/pull-up resistances, or use the host
MCU’s GPIOs to control the voltage level of these pins when powering on ESP32-C3 family.
After reset, the strapping pins work as normal-function pins.
Refer to Table 2for a detailed boot-mode configuration of the strapping pins.
Table 2: Strapping Pins
Booting Mode 1
Pin Default SPI Boot Download Boot
GPIO2 N/A 1 1
GPIO8 N/A Don’t care 1
GPIO9 Pull-up 1 0
Enabling/Disabling ROM Code Print During Booting
Pin Default Functionality
GPIO8 N/A
When the value of eFuse field EFUSE_UART_PRINT_CONTROL is
0 (default), print is enabled and not controlled by GPIO8.
1, if GPIO8 is 0, print is enabled; if GPIO8 is 1, it is disabled.
2, if GPIO8 is 0, print is disabled; if GPIO8 is 1, it is enabled.
3, print is disabled and not controlled by GPIO8.
Controlling JTAG Signal Source During Booting
Pin Default Functionality
GPIO10 N/A
When the value of eFuse bit EFUSE_STRAP_JTAG_SEL is
0 (default), JTAG signals come from USB Serial/JTAG controller.
1, if GPIO10 is 0, JTAG signals come from chip pins;
if GPIO10 is 1, JTAG signals come from USB Serial/JTAG controller.
1The strapping combination of GPIO8 = 0 and GPIO9 = 0 is invalid and will trigger unexpected
behavior.
Figure 10 shows the setup and hold times for the strapping pin before and after the CHIP_PU signal goes high.
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Details about the parameters are listed in Table 3.
CHIP_PU
t1 t0
Strapping pin
VIL_nRST
VIH
Figure 10: Setup and Hold Times for the Strapping Pin
Table 3: Parameter Descriptions of Setup and Hold Times for the Strapping Pin
Min
Parameter Description (ms)
t0Setup time before CHIP_PU goes from low to high 0
t1Hold time after CHIP_PU goes high 3
2.9 GPIO
Note:
The content below is excerpted from Section General Purpose Input / Output Interface (GPIO) in ESP32-C3 Family Datasheet.
ESP32-C3 family has 22 GPIO pins which can be assigned various functions by configuring corresponding
registers. Besides digital signals, some GPIOs can be also used for analog functions, such as ADC.
All GPIOs have selectable internal pull-up or pull-down, or can be set to high impedance. When these GPIOs are
configured as an input, the input value can be read by software through the register. Input GPIOs can also be set
to generate edge-triggered or level-triggered CPU interrupts. All digital IO pins are bi-directional, non-inverting
and tristate, including input and output buffers with tristate control. These pins can be multiplexed with other
functions, such as the UART, SPI, etc. For low-power operations, the GPIOs can be set to holding state.
The IO MUX and the GPIO matrix are used to route signals from peripherals to GPIO pins. Together they provide
highly configurable I/O. Using GPIO Matrix, peripheral input signals can be configured from any IO pins while
peripheral output signals can be configured to any IO pins. Table 4shows the IO MUX functions of each pin. For
more information about IO MUX and GPIO matrix, please refer to Chapter IO MUX and GPIO Matrix (GPIO,
IO_MUX) in ESP32-C3 Technical Reference Manual.
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Table 4: IO MUX Pin Functions
Name No. Function 0 Function 1 Function 2 Reset Notes
XTAL_32K_P 4 GPIO0 GPIO0 — 0 R
XTAL_32K_N 5 GPIO1 GPIO1 — 0 R
GPIO2 6 GPIO2 GPIO2 FSPIQ 1 R
GPIO3 8 GPIO3 GPIO3 — 1 R
MTMS 9 MTMS GPIO4 FSPIHD 1 R
MTDI 10 MTDI GPIO5 FSPIWP 1 R
MTCK 12 MTCK GPIO6 FSPICLK 1* G
MTDO 13 MTDO GPIO7 FSPID 1 G
GPIO8 14 GPIO8 GPIO8 — 1 —
GPIO9 15 GPIO9 GPIO9 — 3 —
GPIO10 16 GPIO10 GPIO10 FSPICS0 1 G
VDD_SPI 18 GPIO11 GPIO11 — 0 —
SPIHD 19 SPIHD GPIO12 — 3 —
SPIWP 20 SPIWP GPIO13 — 3 —
SPICS0 21 SPICS0 GPIO14 — 3 —
SPICLK 22 SPICLK GPIO15 — 3 —
SPID 23 SPID GPIO16 — 3 —
SPIQ 24 SPIQ GPIO17 — 3 —
GPIO18 25 GPIO18 GPIO18 — 0 USB, G
GPIO19 26 GPIO19 GPIO19 — 0* USB
U0RXD 27 U0RXD GPIO20 — 1 G
U0TXD 28 U0TXD GPIO21 — 1 —
Reset
The default configuration of each pin after reset:
•0- input disabled, in high impedance state (IE = 0)
•1- input enabled, in high impedance state (IE = 1)
•2- input enabled, pull-down resistor enabled (IE = 1, WPD = 1)
•3- input enabled, pull-up resistor enabled (IE = 1, WPU = 1)
•0* - input disabled, pull-up resistor enabled (IE = 0, WPU = 0, USB_WPU = 1). See details in Notes
•1* - When the value of eFuse bit EFUSE_DIS_PAD_JTAG is
0 (default), input enabled, pull-up resistor enabled (IE = 1, WPU = 1)
1, input enabled, in high impedance state (IE = 1)
We recommend pulling high or low GPIO pins in high impedance state to avoid unnecessary power
consumption. You may add pull-up and pull-down resistors in your PCB design referring to Table DC
Characteristics (3.3 V, 25 °C) in ESP32-C3 Family Datasheet, or enable internal pull-up and pull-down resistors
during software initialization.
Notes
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•R- These pins have analog functions.
•USB - GPIO18 and GPIO19 are USB pins. The pull-up value of a USB pin is controlled by the pin’s pull-up
value together with USB pull-up value. If any of the two pull-up values is 1, the pin’s pull-up resistor will be
enabled. The pull-up resistors of USB pins are controlled by USB_SERIAL_JTAG_DP_PULLUP bit (1 by
default).
•G- These pins have glitches during power-up. See details in Table 5.
Table 5: PowerUp Glitches on Pins
Typical Time Period
Pin Glitch (ns)
MTCK Low-level glitch 5
MTDO Low-level glitch 5
GPIO10 Low-level glitch 5
U0RXD Low-level glitch 5
GPIO18 Pull-up glitch 50000
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3. PCB Layout Design
This chapter takes ESP32-C3-WROOM-02 module as an example to illustrate key points of ESP32-C3 family
PCB layout.
Figure 11: ESP32C3 Family PCB Layout
3.1 General Principles of PCB Layout
We recommend a four-layer PCB design.
• The first layer is the TOP layer for signal traces and components.
• The second layer is the GND layer without signal traces being routed so as to ensure a complete GND
plane.
• The third layer is the POWER layer where a GND plane should be applied to better isolate the RF module
and crystal. It is acceptable to route signal traces on this layer, provided that there is a complete GND plane
under the RF module and crystal.
• The fourth layer is the BOTTOM layer, where power traces are routed. It is not recommended to place any
components on this layer.
Below are the suggestions for a two-layer PCB design.
• The first layer is the TOP layer for traces and components.
• The second layer is the BOTTOM layer. Please do not place any components on this layer and keep traces
to a minimum. Ideally, it should be a complete GND plane.
3.2 Placement of Module on the Base Board
If you design an on-board module, please pay attention to the placement of the module on the base board. The
aim is to minimize the impact of the base board on the module’s antenna performance.
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The module should be placed as close to the edge of the base board as possible. The PCB antenna area should
be placed outside the base board whenever possible. In addition, the feed point of the antenna should be closest
to the board, as shown in Figure 13 and Figure 12.
123
4
5
Base board
Figure 12: Placement of ESP32C3 Modules on Base Board. Antenna Feed Point on the Right
1 2 3
4
5
Base board
Figure 13: Placement of ESP32C3 Modules on Base Board. Antenna Feed Point on the Left
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Note:
In Figure 12, the recommended position of ESP32-C3 modules (feed point on the right) on the base board should be:
• Position 3, 4: Highly recommended;
• Position 1, 2, 5: Not recommended.
In Figure 13, the recommended position of ESP32-C3 modules (feed point on the left) on the base board should be:
• Position 1, 5: Highly recommended;
• Position 2, 3, 4: Not recommended.
If the positions recommended are not feasible, please make sure that the module is not covered by any metal
shell. Besides, the antenna area of the module and the area 15 mm outside the antenna should be kept clean,
(namely no copper, routing, components on it) as shown in Figure 14.
Base board
Min15
6
Unit: mm
: Clearance Area
Min15
Min15
Figure 14: Keepout Zone for ESP32C3 Module’s Antenna on the Base Board
If there is base board under the antenna area, it is recommended to cut it off to minimize its impact on the
antenna. When designing an end product, pay attention to the impact of enclosure on the antenna.
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3.3 Power Supply
Figure 15: ESP32C3 Family Power Traces in a Fourlayer PCB Design
• Four-layer PCB design is recommended over two-layer design. Route the power traces on the fourth
(bottom) layer whenever possible. Vias are required for the power traces to go through the layers and get
connected to the pins on the top layer. There should be at least two vias if the main power traces need to
cross layers. The drill diameter on other power traces should be no smaller than the width of the power
traces.
• The 3.3 V power traces, highlighted in yellow, are routed as shown in Figure 15. The width of the main
power traces should be at least 20 mil. The width of the power traces for pin 2 and pin 3 should be at least
15 mil. The width of other power traces is preferably 10 mil.
• As shown in Figure 16, we recommend connecting the capacitor to ground in the LC filter circuit near pin 2
and pin 3 (analog power supply pins) to the third and fourth layer through a via, and maintaining a keep-out
area on other layers.
Figure 16: ESP32C3 Family Stub in a Fourlayer PCB Design
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