Note: 

    1. When it is recommended to use, the I2C bus port external on-resistor as shown in the figure R1-R3 is recommended to use 2.2K-10K according to the MCU used;

    2, in order to reduce the crosstalk of the system signal, it is recommended that the MCU of the product be isolated from the positive electrode of the FM1668 power supply series 1N4148 diode, if the program interference is not large and there is no adverse phenomenon such as logic confusion, the diode is not needed.
    3, PCB wiring, as shown in the figure above, C2 should be placed close to the chip VDD foot and its connection should be as short as possible, C2's negative extreme (ground) should also be as short as possible with the chip's 22nd foot connection, if the ground around the far to the 22nd foot, then C2 decoupling effect on FM1668 is almost invalid.