Espressif Systems ESP32 Series Instruction Manual

ESP32 Hardware Design Guidelines
Version 2.1
Espressif Systems

About This Guide
The guidelines outline recommended design practices when developing standalone or add-on systems based on
the ESP32 series of products, including ESP32, the ESP32-WROOM-32(ESP-WROOM-32) module, and ESP32-
DevKitC — the development board.
About This Guide
This document provides the specifications of ESP32 hardware.
Revision History
For the revision history of this document, please refer to the last page.
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Disclaimer and Copyright Notice
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PROVIDED AS IS WITH NO WARRANTIES WHATSOEVER, INCLUDING ANY WARRANTY OF MERCHANTABIL-
ITY, NON-INFRINGEMENT, FITNESS FOR ANY PARTICULAR PURPOSE, OR ANY WARRANTY OTHERWISE
ARISING OUT OF ANY PROPOSAL, SPECIFICATION OR SAMPLE.
All liability, including liability for infringement of any proprietary rights, relating to use of information in this docu-
ment is disclaimed. No licenses express or implied, by estoppel or otherwise, to any intellectual property rights
are granted herein. The Wi-Fi Alliance Member logo is a trademark of the Wi-Fi Alliance. The Bluetooth logo is a
registered trademark of Bluetooth SIG.
All trade names, trademarks and registered trademarks mentioned in this document are property of their respective
owners, and are hereby acknowledged.
Copyright © 2018 Espressif Inc. All rights reserved.

Contents
1 Overview 6
2 Schematic Checklist and PCB Layout Design 7
2.1 Schematic Checklist 7
2.1.1 Power Supply 8
2.1.1.1 Digital Power Supply 8
2.1.1.2 Analog Power Supply 8
2.1.2 Power-on Sequence and System Reset 9
2.1.2.1 Power-on Sequence 9
2.1.2.2 Reset 10
2.1.3 Flash 10
2.1.4 Crystal Oscillator 10
2.1.4.1 External Clock Source (Compulsory) 10
2.1.4.2 RTC (Optional) 12
2.1.5 RF 12
2.1.6 ADC 12
2.1.7 External Capacitor 13
2.1.8 UART 13
2.2 PCB Layout Design 14
2.2.1 Standalone ESP32 Module 14
2.2.1.1 General Principles of PCB Layout 14
2.2.1.2 Positioning a ESP32 Module on a Base Board 15
2.2.1.3 Power Supply 16
2.2.1.4 Crystal Oscillator 17
2.2.1.5 RF 18
2.2.1.6 External RC 19
2.2.1.7 UART 19
2.2.1.8 Touch Sensor 19
2.2.2 ESP32 as a Slave Device 20
2.2.3 Typical Layout Problems and Solutions 21
2.2.3.1 Q: The current ripple is not large, but the Tx performance of RF is rather poor. 21
2.2.3.2 Q: The power ripple is small, but RF Tx performance is poor. 22
2.2.3.3 Q: When ESP32 sends data packages, the power value is much higher or lower than the
target power value, and the EVM is relatively poor. 22
2.2.3.4 Q: Tx performance is not bad, but the Rx sensitivity is low. 22
3 Hardware Development 23
3.1 ESP32-PICO-D4 Module 23
3.2 ESP32-WROOM-32(ESP-WROOM-32) Module 23
3.3 ESP32-WROOM-32D(ESP-WROOM-32D) Module 24
3.4 ESP32-WROOM-32U Module 24
3.5 ESP32-WROVER Module 25
3.6 Notes on Using Modules 26
3.7 ESP32-DevKitC Development Board 26

3.8 ESP-WROVER-KIT Development Board 27
4 Applications 29
4.1 UART to Wi-Fi Smart Device 29
4.2 ESP32-PICO-KIT Mini Development Kit 29
4.3 ESP32-LyraT Smart Audio Platform 29

List of Tables
1 Pin Definition of UART Interfaces 29

List of Figures
1 ESP32 Schematics 7
2 ESP32 Digital Power Supply Pins 8
3 ESP32 Analog Power Supply Pins 9
4 ESP32 Flash 10
5 ESP32 Crystal Oscillator 11
6 ESP32 Crystal Oscillator (RTC) 12
7 ESP32 RF Matching Schematics 12
8 ESP32 External Capacitor 13
9 ESP32 UART 13
10 ESP32 PCB Layout 14
11 ESP32 Module Antenna Position on Base Board 15
12 Keepout Zone for ESP32 Module’s Antenna on the Base Board 16
13 ESP32 Power Supply Design 17
14 ESP32 Crystal Oscillator Layout 18
15 ESP32 RF Layout 18
16 A Typical Touch Sensor Application 19
17 Electrode Pattern Requirements 20
18 Sensor Track Routing Requirements 20
19 PAD/TV Box Layout 21
20 ESP32-PICO-D4 Module 23
21 ESP32-WROOM-32(ESP-WROOM-32) Module 24
22 ESP32-WROOM-32D(ESP-WROOM-32D) Module 24
23 ESP32-WROOM-32U Module 25
24 ESP32-WROVER Module 25
25 Front Side of ESP32-DevKitC 27
26 Front Side of the ESP-WROVER-KIT Layout 27
27 Rear Side of the ESP-WROVER-KIT Layout 28

1. OVERVIEW
1. Overview
ESP32 is a single 2.4 GHz Wi-Fi and Bluetooth combo chip designed with TSMC ultra-low-power 40 nm technol-
ogy. It is designed to achieve the best power and RF performance, robustness, versatility, and reliability in a wide
variety of applications and different power profiles.
ESP32 is a highly-integrated solution for Wi-Fi + Bluetooth applications in the IoT industry with around 20 external
components. ESP32 integrates the antenna switch, RF balun, power amplifier, low noise receive amplifier, filters,
and power management modules. As such, the entire solution occupies minimal Printed Circuit Board (PCB)
area.
ESP32 uses CMOS for single-chip fully-integrated radio and baseband, and also integrates advanced calibration
circuitries that allow the solution to dynamically adjust itself to remove external circuit imperfections or adjust to
changes in external conditions. As such, the mass production of ESP32 solutions does not require expensive and
specialized Wi-Fi test equipment.
The ESP32 series of chips include ESP32-D0WDQ6, ESP32-D0WD, ESP32-D2WD and ESP32-S0WD. For details
of part number and ordering information, please refer to ESP32 Datasheet.
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2. SCHEMATIC CHECKLIST AND PCB LAYOUT DESIGN
2. Schematic Checklist and PCB Layout Design
ESP32’s integrated circuitry requires only 20 resistors, capacitors and inductors, one crystal and one SPI flash
memory chip. ESP32 integrates the complete transmit/receive RF functionality including the antenna switches, RF
balun, power amplifier, low noise receive amplifier, filters, power management module, and advanced calibration
circuitries.
ESP32’s high integration allows for simple peripheral circuit design. This document details ESP32 schematics and
PCB layout design.
While the high level of integration makes the PCB design and layout process simple, the performance of the system
strongly depends on system design aspects. To achieve the best overall system performance, please follow the
guidelines specified in this document for circuit design and PCB layout. All the common rules associated with
good PCB design still apply and this document is not an exhaustive list of good design practices.
2.1 Schematic Checklist
ESP32 schematics is as shown in Figure 1.
CHIP_PU
GPIO35
SCK/CLK
SCS/CMD
SENSOR_VP
SHD/SD2 SWP/SD3
SDI/SD1
SDO/SD0
SENSOR_VN
GPIO34
GPIO32
U0TXD
GPIO33
GPIO25
GPIO26 GPIO27 GPIO14 GPIO12 GPIO15 GPIO13 GPIO2 GPIO0 GPIO4
GPIO16
GPIO17
SDO/SD0
SDI/SD1
SCK/CLK
SWP/SD3
SCS/CMD
SHD/SD2
GPIO18
GPIO5
GPIO23
GPIO19
GPIO22
U0RXD
GPIO21
CHIP_PU
VDD33
GND
VDD33
VDD33
GND
GND
VDD_SDIO
VDD33
GND
GND
GND
GNDGND
GND
GND
GND
VDD_SDIO
VDD33
GND
GNDGND
GND
GND
GND
GND GND
GNDGND
VDD33
GND
C18
1uF
C14
2.7pF±0.1pF
R1 20K
C13
10uF
C22
0.1uF
C5
10nF
C21
NC
L5 2.0nH
C9
0.1uF
C2
22pF
R2 0R
C15
2.0pF±0.1pF
L4 2.7nH±0.1nH
C10
0.1uF
C17
270pF(NC)
C6 3.3nF
C20
1uF
C16
270pF(NC)
C3
100pF
R4
10K
C4
0.1uF
ANT1
PCB ANT
1
2
C11
1uF
C12
NC
U1
40MHz+/-10ppm
XIN
1
GND
2XOUT 3
GND 4
C19
0.1uF
R3 499R
U2 ESP32
VDDA
1
LNA_IN
2
VDD3P3
3
VDD3P3
4
SENSOR_VP
5
SENSOR_CAPP
6
SENSOR_CAPN
7
SENSOR_VN
8
CHIP_PU
9
VDET_1
10
VDET_2
11
32K_XP
12
32K_XN
13
GPIO25
14
GPIO26
15
GPIO27
16
MTMS
17
MTDI
18
VDD3P3_RTC
19
MTCK
20
MTDO
21
GPIO2
22
GPIO0
23
GPIO4
24
VDD_SDIO 26
GPIO16 25
GPIO17 27
SD_DATA_2 28
SD_DATA_3 29
SD_CMD 30
SD_CLK 31
SD_DATA_0 32
GND 49
SD_DATA_1 33
GPIO5 34
GPIO18 35
GPIO19 38
CAP2 47
VDDA 43
XTAL_N 44
XTAL_P 45
GPIO23 36
U0TXD 41
GPIO22 39 GPIO21 42
VDD3P3_CPU 37
CAP1 48
VDDA 46
U0RXD 40
C1
22pF
U3 FLASH
/CS
1
DO 2
/WP 3
GND
4
DI 5
CLK
6
/HOLD
7
VCC 8
Figure 1: ESP32 Schematics
Any basic ESP32 circuit design may be broken down into seven major sections:
• Power supply
• Power-on sequence and system reset
• Flash
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2. SCHEMATIC CHECKLIST AND PCB LAYOUT DESIGN
• Crystal oscillator
• RF
• External capacitors
• UART
2.1.1 Power Supply
For further details of using the power supply pins, please refer to Section 2.3 Power Scheme in ESP32 Datasheet.
2.1.1.1 Digital Power Supply
Pin19 and Pin37 are the power supply pins for RTC and CPU, respectively. The digital power supply operates in
a voltage range of 1.8V ~3.6V. We recommend adding extra filter capacitors of 0.1 µF close to the digital power
supply pins.
The voltage of VDD_SDIO is produced by the internal LDO. It can be used as the power supply for the external
circuitry, with a maximum current of about 40 mA when using the 3.3V LDO. When the VDD_SDIO outputs 1.8V,
the value of GPIO12 should be set to 1 when the chip boots. The user can add a 1 µF filter capacitor close to
VDD_SDIO. When the VDD_SDIO outputs 3.3V, the value of GPIO12 is 0 (default) when the chip boots and it is
recommended that users add 2 kΩresistor to ground and a 1 µF capacitor close to VDD3P3_RTC.
When using VDD_SDIO as the power supply pin for the external 3.3V flash/PSRAM, the supply voltage should be
2.7V or above, so as to meet the requirements of flash/PSRAM’s working voltage.
GPIO12
GPIO15 GPIO13 GPIO2 GPIO0 GPIO4
GPIO16
GPIO17
SDO/SD0
SDI/SD1
SCK/CLK
SWP/SD3
SCS/CMD
SHD/SD2
GPIO18
GPIO5
GPIO23
GPIO19
GND
VDD33
GND
VDD_SDIO
VDD33
GND
C18
1uF
C4
0.1uF
C19
0.1uF
ESP32
MTDI
18
VDD3P3_RTC
19
MTCK
20
MTDO
21
GPIO2
22
GPIO0
23
GPIO4
24
VDD_SDIO 26
GPIO16 25
GPIO17 27
SD_DATA_2 28
SD_DATA_3 29
SD_CMD 30
SD_CLK 31
SD_DATA_0 32
SD_DATA_1 33
GPIO5 34
GPIO18 35
GPIO19 38
VDDA 43
XTAL_N
44
XTAL_P 45
GPIO23 36
U0TXD 41
GPIO22 39 GPIO21 42
VDD3P3_CPU 37
U0RXD 40
Figure 2: ESP32 Digital Power Supply Pins
2.1.1.2 Analog Power Supply
Pin1, Pin43 and Pin46 are the analog power supply pins. Pin3 and Pin4 are the power supply pins for the power
amplifiers. It should be noted that the sudden increase in current draw, when ESP32 is in transmission mode, may
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2. SCHEMATIC CHECKLIST AND PCB LAYOUT DESIGN
cause a power rail collapse. Therefore, it is highly recommended to add another 10 µF capacitor to the power
trace, which can work in conjunction with the 0.1 µF capacitor. LC filter circuit needs to be added to near the
power pin so as to suppress high-frequency harmonics. The inductor’s rated current is preferably 500 mA and
above.
SENSOR_VP
VDD33
GND
VDD33
VDD33
GND
GND
GND
GNDGND
GND
GND
GNDGND
R1 20K
C14
2.7pF±0.1pF
C13
10uF
C5
10nF
C9
0.1uF
L5 2.0nH
C21
NC
C15
2.0pF±0.1pF
R2 0R
C10
0.1uF
L4 2.7nH±0.1nH
C16
270pF(NC)
C20
1uF
C6 3.3nF
C3
100pF
ANT1
PCB ANT
1
2
C12
NC
C11
1uF
VDDA
1
LNA_IN
2
VDD3P3
3
VDD3P3
4
SENSOR_VP
5
6
GND 49
CAP2 47
VDDA
43
XTAL_N 44
XTAL_P 45
GPIO21 42
CAP1 48
VDDA 46
Figure 3: ESP32 Analog Power Supply Pins
Notice:
• The recommended voltage of the power supply for ESP32 is 3.3V, and its recommended output current
is 500 mA or more.
• It is suggested that users add an ESD tube at the power entrance.
2.1.2 Power-on Sequence and System Reset
2.1.2.1 Power-on Sequence
ESP32 uses a 3.3V system power supply. The chip should be activated after the power rails have stabilized. This is
achieved by delaying the activation of CHIP_PU (Pin9) by time T after the 3.3V rails have been brought up. The rec-
ommended delay time (T) is given by the parameter of the RC(R = 10 kΩ, C = 0.1 µF) circuit. For reference design,
please refer to Figure ESP-WROOM-32 Peripheral Schematics in the ESP-WROOM-32 Datasheet.
Notice:
If CHIP_PU is driven by a power management chip, then the power management chip controls the
ESP32 power state. When the power management chip turns on/off Wi-Fi through the high/low level
on GPIO, a pulse current may be generated. To avoid level instability on CHIP_PU, an RC delay (R = 10
kΩ, C = 0.1 µF) circuit is required.
Espressif Systems 9 ESP32 Hardware Design Guidelines V2.1