Onboard BK3431Q Application Development

The BK3431Q chip is a highly integrated Bluetooth 4.2 low energy (LE) single-mode device. Its data rate can be set to up to 2 Mbit/s. It integrates a high-performance radio frequency (RF) transceiver, baseband, ARM9E core, feature-rich peripheral units, programmable protocol, and profile to support Bluetooth LE applications. The built-in Flash memory makes it suitable for customized applications. Therefore, you can develop your own embedded Bluetooth products.

RF schematic diagram

The RF schematic diagram mainly consists of the RF, crystal oscillator, and chip filter.

Reference schematic diagram of a 40-pin chip:

Reference schematic diagram of a 32-pin chip:

PCB design

During PCB design, place the chip, crystal, and RF trace on the top layer. At the bottom layer, ensure that the GND terminals at the bottom of the chip, crystal, and RF trace are connected to form a completed GND. Therefore, make the return circuit shortest and reduce interference.

Things to note

• The default width of the microstrip on the RF channel is 12 mil in a 4-layer board. When making the PCB, you need to confirm with the board manufacturer to make a microstrip with a characteristic impedance of 50Ω. To reduce the signal loss, the RF trace from the RF pin to the antenna should be as short as possible, and the components should be placed in a compact way.

  

• The RF pad is placed between the chip matching position and the antenna matching position. The via should not be placed on the center of the pad but close to the edge of the center pad.

  

• The trace of the crystal oscillator should be as short as possible. To prevent electromagnetic interference (EMI), add ground vias around the crystal oscillator.

  • A 16 MHz, 9 pF 4-pin crystal oscillator works as the main crystal oscillator of the board.

  • A 2-pin crystal oscillator is a 32.768 kHz clock crystal oscillator. For more information about how to choose a crystal oscillator, see the type selection guide.

    

• Pay attention to the selection of power inductors. A complete bill of materials (BOM) will be attached.

• The distance between the antenna and the board edge is more than 12 mil, and the height of the antenna protruding from the lighting board is more than 7 mm. Take into account the antenna performance and luminous effect.

Onboard antenna design

Different types of antennas are supported, such as the monopole, helical antenna, PCB antenna, FPC antenna, and ceramic antenna. A certain clearance must be guaranteed around the antenna. You can choose a suitable antenna based on the shape and space of the product.

If the following three types of PCB antennas A, B, and C are used, the value of E2 on a two-layer board or four-layer board should be between 1.8 nH and 4.7nH. Meanwhile, E1 and E3 do not need surface-mount technology (SMT) processing. However, if a precision test is required, you need targeted debugging for different backplanes, because the size of the ground plane leads to differences in impedance.

• PCB antenna A

  

• PCB antenna B

  

• PCB antenna C

  

For A60 light bulbs and similar products, the PCB antenna is usually used. Under acceptable shadow conditions, try to extend the PCB antenna out of the light board to ensure the antenna efficiency. Meanwhile, choose an antenna with a narrow vertical distance, such as the PCB antenna B shown above.

For strip lights, you can choose the PCB antenna C.

Bill of materials

The following table lists the bill of materials for the module under the condition of this PCB trace and completely tested RF performance under 85°C normal temperature.

The following table lists the bill of materials for modules under 105°C high temperature.

Test jig preparation

• Break out the test points for all pins in use.
• If there are strip lights and infrared requirements, the test jig documents must indicate that the test points need to be connected to the strip lights and infrared devices with jumper wires, which can be led out by an ejector pin.
• If a large plugin exists, hollow out the test jig properly to avoid interference.
• In the onboard solution, the antenna should be placed outwards, the test jig around the antenna should be cleared, and an RF connector should be added to the test jig.

SPI flashing

Backplane SPI flashing

Prepare a USB to SPI adapter board that has a writer and USB cable. The writer provides two SPI interfaces, SW SPI and HW SPI, corresponding to two flashing methods. We use the SW SPI interface.

For the wiring of SW SPI, the wire sequence is shown as follows:

Procedure

1. Open the flashing software and select the desired firmware to be downloaded. For more information about the firmware location, see the subsequent things to note.
2. Click Download Flash to start downloading the firmware.
3. Wait for the download to complete, and make sure that the download status is Program downloaded successfully.
4. After the flashing is successful, remove the writer, and power on again to search for Bluetooth broadcasts.

Things to note

• The location and name of the firmware in the folder are shown as follows.

  

• Make sure that the download mode is SPI SOFT Software.

• Make sure that the chip erase method is Erase All Spaces.

SPI flashing for backplane with test jig

Prepare a USB to SPI adapter board that has a writer and USB cable. The writer provides two SPI interfaces, SW SPI and HW SPI, corresponding to two flashing methods.
Procedure

1. Insert the USB-SPI board into the backplane in the correct direction, as shown below. Make sure the correct SPI interface is inserted.

   

2. Open the MXCHIP tool and repeat the above module SPI flashing method.

Production test

Flash boot firmware

1. Flash the boot firmware on the backplane to the module by grounding the I/O0 lead on the backplane.
   The figure below shows the wiring method of connecting the I/O0 lead on the backplane to the ground.

   

   

2. Connect the test jig to the PC. The PC is connected to the backplane through a serial-to-USB adapter and powers the backplane and test jig. The backplane has a group of electrical connectors and two indicator signal cables connected to the test jig.

   

Firmware flashing and authorization

Connect the test jig in the same manner as boot flashing but disconnect the I/O0 from GND of the backplane. Then, you can start flashing and authorization.

1. Open the software Cloud Module Burning Authorization Platform. Click File > Set Up and set Burning Baud to 150000 and Test Baud to 9600.

   

2. Click Enter Token on the main interface. In the Firmware Update > Enter Token field, enter the token of BK3431Q. In the Select work station field, select Burning Authorization from the dropdown list and click OK.

   

3. Select COM Port for the connected serial-to-USB adapter.

4. Click Run and wait until the flashing is completed. When authorization and flashing are completed, the interface shows Succeed.

   

Fixed frequency test

Firmware and host:

• Host test wiring: 3V3, GND, UART1 TX, and UART1 RX

• How to use the host:

  

  1. Select the correct COMM port. The COMM port must be below COM10. Otherwise, the software might not recognize it.
  2. Click Open.
  3. In the HW TEST section, click Enter DUT. At this time, test mode enable will be displayed in the command window.
  4. In the DateType field, select the SINWAVE or NORMAL mode.
  5. In the PacketType field, select NULL.
  6. Check BLE.
  7. In the SW TEST section, set up the parameters.
  8. Click Config to start the test.