Espressif Systems ESP8266 Series Instruction Manual

www.espressif.com
ESP8266
Hardware Design Guidelines
Version 2.4
Espressif Systems
Copyright © 2018

About This Guide
This document provides product information of ESP8266EX series, including ESP8266EX
chip, ESP-LAUNCHER development board and ESP8266EX modules.
Release Notes
Documentation Change Notification
Espressif provides email notifications to keep customers updated on changes to
technical documentation. Please subscribe at https://www.espressif.com/en/subscribe.
Certification
Download certificates for Espressif products from https://www.espressif.com/en/
certificates.!
Date
Version
Release Notes
2015.12
V1.3
Initial release.
2016.01
V1.4
Update Section 1.5.2, Section 1.5.3 and Section 1.6.
2016.06
V1.5
Update Section 3.1.
2016.07
V1.6
Update Section 2.1.
2017.01
V2.0
Updated the minimum voltage of ESP8266EX to 2.5V;
Updated Table 1-1.
2017.04
V2.1
Updated the chip’s output impedance from 50Ωto 39+j6 Ω;
Added a note that the size of ESP-LAUNCHER’s Flash1 and Flash2 is 32
Mbit;
Updated Section 1.4.5.
2017.06
V2.2
Updated Section 1.4.2.
2018.04
V2.3
Updated the name of the document from “ESP8266 System Description”
to “ESP8266 Hardware Design Guidelines”;
Updated all the figures in the document;
Updated Section 1.4 Schematic Checklist;
Updated Chapter 3 ESP8266EX Module.
2018.12
V2.4
Updated description in Section 1.4.2 about reset;
Updated formatting.

Table of Contents
1. ESP8266EX 1............................................................................................................................
1.1. Overview!1"....................................................................................................................................
1.2. Specifications!2".............................................................................................................................
1.3. Pin Definitions!3"............................................................................................................................
1.4. Schematic Checklist!5"..................................................................................................................
1.4.1. Power Supply!6"...............................................................................................................
1.4.2. Power-on Sequence and Power Reset!8".........................................................................
1.4.3. Flash!8".............................................................................................................................
1.4.4. Crystal Oscillator!9"..........................................................................................................
1.4.5. RF!10"...............................................................................................................................
1.4.6. External Resistor 12K!10".................................................................................................
1.4.7. UART!10"...........................................................................................................................
1.5. Slave SDIO/SPI!11"........................................................................................................................
1.6. PCB Layout Design!12"..................................................................................................................
1.6.1. General Principles of PCB Layout Design!12"..................................................................
1.6.2. Positioning a ESP32 Module on a Base Board!13"..........................................................
1.6.3. Standalone ESP8266EX Module!14"................................................................................
1.6.4. ESP8266EX as a Slave Device!17"...................................................................................
1.6.5. Typical Layout Problems and Solutions!18"......................................................................
1.7. PCB Layout Design!19"..................................................................................................................
1.7.1. UART to Wi-Fi Smart Device!19"......................................................................................
1.7.2. Sensor!19".........................................................................................................................
1.7.3. Smart Light!20".................................................................................................................
1.7.4. Smart Plug!20"..................................................................................................................
2. ESP-LAUNCHER 21..................................................................................................................
2.1. Overview!21"..................................................................................................................................
2.2. Modules and Interfaces!21"............................................................................................................
2.3. Schematics!24"..............................................................................................................................
2.3.1. Interfaces!24"....................................................................................................................
2.3.2. 5V Power Supply!25"........................................................................................................
2.3.3. Test Module!25"................................................................................................................

2.4. Test Board!26"................................................................................................................................
3. ESP8266EX Module 27.............................................................................................................
3.1. ESP-WROOM-S2!27".....................................................................................................................
3.2. ESP-WROOM-02!27".....................................................................................................................
3.3. ESP-WROOM-02D/ESP-WROOM-02U!28...................................................................................

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1. ESP8266EX
1. ESP8266EX
1.1. Overview
Espressif’s ESP8266EX delivers a highly integrated Wi-Fi SoC solution to meet the
continuous demand for efficient power usage, compact design and reliable performance in
the industry.
With its complete and self-contained Wi-Fi networking capabilities, ESP8266EX can
perform either as a standalone application, or as a slave to a host MCU. When ESP8266EX
hosts an application, it promptly boots up from the external flash. The integrated high-
speed cache optimizes the system's performance and memory.
Also, ESP8266EX can be applied to any micro-controller design as a Wi-Fi adaptor through
SPI/SDIO or I2C/UART interfaces.
Besides the Wi-Fi functionalities, ESP8266EX also integrates an enhanced version of
Tensilica’s L106 Diamond series 32-bit processor and on-chip SRAM. It can be interfaced
with external sensors and other devices through the GPIOs, resulting in low development
cost at early stage and minimum footprint. Software Development Kit (SDK) provides
sample codes for various applications.
ESP8266EX integrates antenna switches, RF balun, power amplifier, low-noise receive
amplifier, filters and power management modules. The compact design minimizes the PCB
size and the external circuitry.
ESP8266EX enables sophisticated features, such as:
•Fast switching between sleep and wake-up modes for efficient energy use;
•Adaptive radio biasing for low-power operation;
•Advanced signal processing;
•Spur cancellation;
•Radio co-existence mechanisms for common cellular, Bluetooth, DDR, LVDS, LCD
interference mitigation.
Figure 1-1 shows the functional blocks of ESP8266EX.
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1. ESP8266EX
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Figure 1-1. ESP8266EX Block Diagram
1.2. Specifications
RF balun
Switch
RF
receive
RF
transmit
Analog
receive
Analog
transmit
PLL VCO 1/2 PLL
Digital baseband
MAC Interface
PMU Crystal Bias circuits SRAM PMU
SDIO
I2C
PWM
ADC
SPI
UART
GPIO
I2S
Flash
Registers
CPU
Sequencers
Accelerator
Table 1-1. ESP8266EX Specifications
Categories
Items
Parameters
Wi-Fi
Standard
FCC/CE/TELEC/SRRC
Protocols
802.11 b/g/n/e/i
Frequency Range
2.4G ~ 2.5G (2400M ~ 2483.5M)
Tx power
802.11 b: ＋20 dBm
802.11 g: ＋17 dBm
802.11 n: ＋14 dBm
Rx Sensitivity
802.11 b: -91 dBm (11 Mbps)
802.11 g: -75 dBm (54 Mbps)
802.11 n: -72 dBm (MCS7)
Antenna
on-board, external, IPEX connector, ceramic chip
Hardware
Peripheral interface
UART/SDIO/SPI/I2C/I2S/IR Remote Control
GPIO/PWM
Operating voltage
2.5V ~ 3.6V
Operating current
Average: 80 mA
Operating temperature range
-40℃~ 125℃
Storage temperature range
-40℃~ 125℃
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1. ESP8266EX
1.3. Pin Definitions
The pin layout for the 32-pin QFN package is illustrated in Figure 1-2.
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Figure 1-2. ESP8266EX Pin Layout
Table 1-2 lists the definitions and functions of each pin.!
Package size
QFN32-pin (5 mm x 5 mm)
External interface
N/A
Software
Wi-Fi mode
Station/SoftAP/SoftAP+Station
Security
WPA/WPA2
Encryption
WEP/TKIP/AES
Firmware upgrade
UART Download/OTA (via network)
Software development
SDK for customized development/cloud server
development
Network Protocols
IPv4, TCP/UDP/HTTP/FTP
User configuration
AT Instruction Set, Cloud Server, Android/ iOS app
Categories
Items
Parameters
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1. ESP8266EX
Table 1-2. ESP8266EX Pin Definitions
Pin
Name
Type
Function
1
VDDA
P
Analog Power 2.5V ~ 3.6V
2
LNA
I/O
RF antenna interface
Chip output impedance=39+j6 Ω. It is suggested that users retain
the π-type matching network which matches the antenna.
3
VDD3P3
P
Amplifier Power 2.5V ~ 3.6V
4
VDD3P3
P
Amplifier Power 2.5V ~ 3.6V
5
VDD_RTC
P
NC (1.1V)
6
TOUT
I
ADC pin. It can be used to test the power-supply voltage of
VDD3P3 (Pin3 and Pin4) and the input power voltage of TOUT (Pin
6). However, these two functions cannot be used simultaneously.
7
CHIP_EN
I
Chip Enable
High: On, chip works properly
Low: Off, small current consumed
8
XPD_DCDC
I/O
Deep-sleep wakeup (need to be connected to EXT_RSTB);
GPIO16
9
MTMS
I/O
GPIO 14; HSPI_CLK
10
MTDI
I/O
GPIO 12; HSPI_MISO
11
VDDPST
P
Digital/IO Power Supply (1.8V ~ 3.3V)
12
MTCK
I/O
GPIO 13; HSPI_MOSI; UART0_CTS
13
MTDO
I/O
GPIO 15; HSPI_CS; UART0_RTS
14
GPIO2
I/O
UART Tx during flash programming; GPIO2
15
GPIO0
I/O
GPIO0; SPI_CS2
16
GPIO4
I/O
GPIO 4
17
VDDPST
P
Digital/IO Power Supply (1.8V ~ 3.3V)
18
SDIO_DATA_2
I/O
Connects to SD_D2 (Series R: 200Ω); SPIHD; HSPIHD; GPIO 9
19
SDIO_DATA_3
I/O
Connects to SD_D3 (Series R: 200Ω); SPIWP; HSPIWP; GPIO 10
20
SDIO_CMD
I/O
Connects to SD_CMD (Series R: 200Ω); SPI_CS0; GPIO 11
21
SDIO_CLK
I/O
Connects to SD_CLK (Series R: 200Ω); SPI_CLK; GPIO 6
22
SDIO_DATA_0
I/O
Connects to SD_D0 (Series R: 200Ω); SPI_MSIO; GPIO 7
23
SDIO_DATA_1
I/O
Connects to SD_D1 (Series R: 200Ω); SPI_MOSI; GPIO 8
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1. ESP8266EX
1.4. Schematic Checklist
The highly-integrated design of ESP8266EX reduces the number of components required.
Besides ESP8266EX, less than 10 resistors and capacitors, one crystal oscillator and one
SPI flash are needed to make a complete module with wireless communication capability.
The following is a detailed description of ESP8266EX schematics, and the layout design
which ensures optimum functionality.
The complete circuit diagram of ESP8266EX is illustrated in Figure 1-3.!
24
GPIO5
I/O
GPIO 5
25
U0RXD
I/O
UART Rx during flash programming; GPIO 3
26
U0TXD
I/O
UART Tx during flash progamming; GPIO 1; SPI_CS1
27
XTAL_OUT
I/O
Connects to crystal oscillator output, can be used to provide BT
clock input
28
XTAL_IN
I/O
Connects to crystal oscillator input
29
VDDD
P
Analog Power 2.5V ~ 3.6V
30
VDDA
P
Analog Power 2.5V ~ 3.6V
31
RES12K
I
Serial connection with a 12 kΩresistor and connect to the ground
32
EXT_RSTB
I
External reset signal (Low voltage level: Active)
Pin
Name
Type
Function
📖Note:
GPIO2, GPIO0, and MTDO are configurable on PCB as the 3-bit strapping register that determines the
booting mode and the SDIO timing mode.
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1. ESP8266EX
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Figure 1-3. ESP8266EX Schematics
The ESP8266EX schematics include seven aspects:
•Power supply
•Power-on sequence and reset
•Flash
•Crystal oscillator
•RF
•External resistor
•UART
1.4.1. Power Supply
1.4.1.1. Digital Power Supply
ESP8266EX has two digital pins for power supply, Pin11 and Pin17. For digital power
supply, there is no need to add additional filter capacitors. The operating voltage range of
digital power supply pins is 1.8V ~ 3.3V.!
GPIO15
RST
SDI/SD1
SDO/SD0
SCK/CLK
SCS/CMD
SWP/SD3
SCK/CLK
SCS/CMD
SHD/SD2
UTXDA
WIFI_ANT
GPIO14 GPIO12
URXD
GPIO13
GPIO16
GPIO0
CH_PU
GPIO2 GPIO4
GPIO5
TOUT
SWP/SD3
SDO/SD0
SDI/SD1
UTXD
SHD/SD2
GND
GND
VDD33
GND
GNDGND
GND
VDD33
GND
VDD33
GND
GND
GND
GND
VDD33
GND
GND
GND
ANT1
1
2
R1
12K±1%
C7
TBD(NC)
C1
6.8pF
C3
0.1uF
L3 4.3nH
C8
1uF(NC)
U3FLASH
/CS
1
DO 2
/WP 3
GND
4
DI 5
CLK
6
/HOLD
7
VCC 8
L1
2.4pF
R3 200R
C4 2.2nH
L2
3.0pF
C6
1uF
U1
26MHz±10ppm
XIN
1
GND
2XOUT 3
GND 4
U2ESP8266EX
VDDA
1
LNA
2
VDD3P3
3
VDD3P3
4
VDD_RTC
5
TOUT
6
CHIP_EN
7
XPD_DCDC
8
MTMS
9
MTDI
10
VDDPST
11
MTCK
12
MTDO
13
GPIO2
14
GPIO0
15
GPIO4
16
VDDPST 17
SD_DATA_2 18
SD_DATA_3 19
SD_CMD 20
SD_CLK 21
SD_DATA_0 22
SD_DATA_1 23
GPIO5 24
U0RXD 25
U0TXD 26
XTAL_OUT 27
XTAL_IN 28
VDDD 29
VDDA 30
RES12K 31
EXT_RSTB 32
GND 33
C5
10uF
R2 499R
C2
6.8pF
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