Hardware Design¶
The CI231 series chip requires only a small number of components to support a wide range of voice and AIOT applications. For the voice part, the chip can support single microphone differential input or single microphone single-ended input, and can also choose whether AEC echo cancellation is required. The user can choose the appropriate circuit according to the function, power consumption and cost requirements of the designed application scheme. The following is a specific description of a typical application reference circuit diagram of the chip.
Apply Reference Circuit Diagram¶
Figure H-1 shows the application reference circuit diagram.
Above is a circuit diagram of the CI231 series chip supporting single microphone differential input and power amplifier output, with AEC application scheme. The chip can use 5V direct power supply, and the user can design according to the corresponding peripheral device specifications in the figure above.
If you want to consider the board level online upgrade function when designing the schematic diagram, you can lead out the UART0 pin to facilitate the firmware upgrade of the Flash inside the main chip through UART0 after the PCB board patch is completed. The PA4 (PG_EN) pin of the chip is pulled inside, and the default mode is upgrade mode. After startup, the upgrade signal from external UART0 port should be detected, and the upgrade will be started directly if there is one. The default boot time of the chip is extended due to the increase of the upgrade mode detection, about 850mS; If the user has high requirements for startup time, you can lead out the PA4 pin, add two 2.2KΩ drop-down resistors to the ground, add a test point in the middle of the connection of two 2.2KΩ resistors, at this time the chip starts in normal mode, startup time is about 350mS, which can shorten the startup time. If you want to upgrade online at this time, you can externally supply the high level to the two intermediate test points connected by 2.2KΩ resistance, pull the PA4 pin high, and then upgrade through UART0.
The chip scheme can choose differential microphone design or single-ended microphone design, the single-ended microphone design in the figure above is recommended. This method is only recommended for applications where the microphone line length is less than 20 cm. If the microphone line length is greater than 20 cm, you need to use a microphone with a shielded line or contact our company to use a differential circuit to enhance the anti-interference ability of the circuit. The power amplifier in the figure above is a class AB power amplifier, and it is recommended to use 8002 power amplifier chip. Users can also choose the power amplifier chip according to the requirements of the scheme. If the power amplifier function is not needed, this part of the circuit can be removed to reduce the cost.
If the user has no special requirements on the power consumption of the solution, it is recommended to directly use the PMU power supply inside the chip. If the power consumption is required, an external DCDC chip can be added to supply power to the chip 1.1V to reduce power consumption. The UART port of the chip supports 5V communication, and the UART0 port in the figure above is connected to 3.3V signal. If you want to connect to 5V, you can add a pull-up resistor connected to 5V on the periphery of the RX and TX pins of UART0, without adding an additional voltage conversion circuit.
PCB Layout Design¶
Power supply circuit¶
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Power cables are routed Power input pay attention to protect overvoltage and surge protection, design TVS device and 4.7 ohm resistance at 5V input, and route the cable first through TVS and then through the resistance to the chip. The cable diameter of the power supply depends on the actual circuit current. The cable width of the 3.3V power supply is not less than 15mil, and the cable width of the 1.2V power supply is not less than 15mil. Try to use the copper coating mode, the power cable as short and thick as possible, the narrowest part of the power cable is not less than 8mil line width, to avoid the power cable to form a closed-loop circuit.
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Power decoupling capacitor The power decoupling capacitor is positioned close to the corresponding pin.
Radio frequency circuit¶
The chip matching network is placed as close to the RFIO pin as possible.
RF wiring must be 50 ohm impedance control, the top layer as far as possible to ensure the integrity of the ground around the RF wiring.
The antenna area must be kept hollow.
Crystal circuit¶
Make sure there is a good wrapping around the crystal.
The copper skin around the top crystal pad is hollowed out, the ground plane of the bottom crystal is complete, and the crystal GND foot is directly connected to the bottom GND through the hole.
Electrostatic protection requirements¶
When designing a two-layer board, try to line the TOP layer to maintain the integrity of the BOTTOM floor plane. If an ESD device is designed, place the ESD device as close as possible to the pin of the plug-in to improve the protection effect.
Apply other considerations¶
- The chip needs an external 16MHz crystal oscillator with an accuracy of 10ppm and a load capacitance of 12pF.
- The chip integrates the PMU management unit, and the PMU contains three Ldos, which provide 3.3V and 1.1V voltage to the chip respectively. If there is no special requirement for power consumption, the solution does not need an external power chip, and the ripple of the external 5V power supply should be less than 300mV.
- Rf devices are sensitive to crystal frequency bias, such as the product working environment is harsh, it is recommended to choose a wide temperature crystal; At the same time, if the PCB is a multi-layer board, it is recommended to hollow out the crystal under the adjacent layer to reduce the influence of parasitic capacitance on the crystal frequency bias.
- RFIO pin must be reserved for matching network, and the wiring must be impedance matching. If the cable length is too long, you are advised to reserve a matching network near the antenna.
- The chip is manufactured by lead-free environmental protection technology. Please set the furnace temperature and time and other parameters according to lead-free standards when SMT welding.
- Pay attention to static electricity when using and packing chips. Antistatic materials are recommended for isolation.