Tuya CBU Module Hardware Design Guideline
Version: 20210128
Hardware Product Development > Hardware Development > RF Design > Wi-Fi module Hardware Design Guideline
1 Application Scope
CBU is a low power embedded Wi-Fi module developed by Tuya Smart. It is composed of a highly integrated radio-frequency identification (RFID) chip BK7231N and a few peripheral components. It supports dual connection of AP and STA, as well as BLE connection.
1.1 Features
- Built-in with a low power 32-bit CPU, 256 KB RAM, and 2 MB flash.
- Basic frequency up to 120 MHz.
- Supports complete functions of 802.11b/g/n.
- Integrates the classical BLE system.
- Maximum output power of +17 dBm in the 802.11b mode.
- Maximum transmission power of 20 dBm in the Bluetooth mode.
- Supports three pairing modes: SmartConfig (EZ), AP, and BLE (available for Android and iOS devices).
- Uses either a PCB antenna or an FPC antenna.
- PCB onboard antennas have a peak gain of 2.5 dBi.
- Operating voltage: 2.1V-3.6V.
- Operating temperature: -40°C-105°C.
For more information, see the CBU Module Datasheet.
2 The Minimum System Circuit
A typical minimum system circuit for the CBU module is illustrated. It includes the CBU module, a 3.3V power supply, and GND connections. Two filter capacitors, C1 (10uF/6.3V) and C2 (0.1uF/10%), are recommended near the power supply pin.
3 Things to Note
3.1 Power Supply Designs Under Different Working Modes
| Working Mode | Working Status (Ta=25°C) | Average Value | Maximum Value (typical) | Unit |
|---|---|---|---|---|
| Bluetooth pairing status | Module in quick pairing status with Wi-Fi indicator flickering quickly | 88 | 130 | mA |
| AP pairing status | Module in access point pairing status with Wi-Fi indicator flickering slowly | 95 | 180 | mA |
| EZ pairing status | Module in quick pairing status with Wi-Fi indicator flickering quickly | 90 | 168 | mA |
| Connected | Module connected to the network with Wi-Fi indicator always on | 90 | 134 | mA |
3.2 RF Power Consumption
| Working Status | Mode | Rate | Transmission Power/Receive | Average Value | Peak Value (typical) | Unit |
|---|---|---|---|---|---|---|
| Transmitting | 11b | 11 Mbit/s | +17 dBm | 180 | 304 | mA |
| Transmitting | 11g | 54 Mbit/s | +15 dBm | 95 | 280 | mA |
| Transmitting | 11n | MCS7 | +14 dBm | 101 | 273 | mA |
| Receiving | 11b | 11 Mbit/s | Continuously receiving | 73 | 76 | mA |
| Receiving | 11g | 54 Mbit/s | Continuous receiving | 75 | 78 | mA |
| Receiving | 11n | MCS7 | Continuously receiving | 75 | 78 | mA |
- The maximum working power consumption of the module is 3.3V/180 mA, and the maximum transient current of transmitting (TX) is 304 mA. For high-current charging during the cold start of large electrolytic capacitors in the peripheral power terminal, it is recommended to select a power supply with a stable power of ≥3.3V/220 mA and a peak current limit of ≥400 mA. Consider the power consumption of other components in the overall product design.
- Power filter capacitors C1 and C2 shall be arranged near the power supply pin.
- Special I/O port description:
- ADC pin: The detected voltage range is 0-2.4V, with conversion precision up to 10 digits.
- UART1 pins (RX1, TX1): These are user serial ports by default and also serve as firmware programming ports. They can be configured as general I/O ports.
- UART2 pins (RX2, TX2): These are log printing ports by default and can be configured as general I/O ports. However, it is recommended not to use the peripheral UART2 for other functions if sufficient pins are available.
3.3 Antenna Clearance Description
Things to note
- Avoid using metal shells or shells with metallic paint or coating in the direction of antenna radiation. Also, avoid using metal screws, metal rivets, or other metal parts that could affect antenna radiation.
- The distance from the top cover to the antenna impacts performance; a greater distance results in less effect on performance.
- The distance from the top-and-bottom shell to the antenna impacts performance; a greater distance results in less effect on performance.
- Keep the module away from horns, power switches, cameras, HDMI, USB, and other high-speed signals to prevent interference.
Placement
- Horizontal placement: It is recommended to place the module at the edge of the backplane with the antenna facing outward. Flush the module GND with the backplane GND, ensuring they are fully connected.
- Embedded placement: Embed the module into the backplane using a slot that is flush with or deeper than the module ground. The side of the slot should be at least 15 mm from the module board edge. A wider slot may offer better performance but might be weaker than horizontal placement.
- Vertical placement: Insert the module into the backplane slot vertically with the antenna facing upward. The module GND and the backplane GND must be fully connected. In ideal conditions, the clearance around the antenna should be at least 15mm.
4 RF Test Items and Indicators
Since antenna performance is susceptible to the distance from the shell and surrounding components, it is recommended to test RF performance after the entire device has been tested. The RF test items and indicators are listed below.
| Serial Number | Test Item | Test Indicator |
|---|---|---|
| 1 | Indoor distance increasing | ≥25m |
| 2 | Outdoor distance increasing | ≥75m |
| 3 | Total radiated power (TRP) of whole device signaling mode (11B 1 Mbit/s test mode) | ≥10 dBm |
| 4 | Whole device TIS | ≤-62 dBm |
Note: Items 3 and 4 should be tested in a dark chamber provided by the antenna manufacturer or certification authorities. These test items apply to most Wi-Fi products, excluding certain special products.
