MF PCB design considerations

Precautions:

  1. For the 850nm infrared fill light, 1W or 3W power lamp beads can be considered, because the lamp beads with higher power can extend the service life, reduce the failure rate and improve the recognition effect

  2. The driving circuit and component parameters of infrared lamp beads and white light lamp beads must be determined according to the actual lamp beads selection and quantity. Because the cost of different circuits is different, the brightness feels different, and the needs of different customers are different, so customers need to choose and adjust parameters according to the actual situation.

  3. 850nm light has certain penetrability. It has been confirmed that the 850nm light of the infrared fill light will penetrate from the periphery and back of the camera module, affecting the imaging, and then affecting the screen image or the recognition effect. Therefore, it is necessary to use 850nm impenetrable materials/paint/tape to block the infrared light scattered from the lamp beads to the inside of the camera between the camera and the fill light. In addition, you can also open the distance between the infrared lamp beads and the camera. Keep the distance above 15mm to reduce the negative impact by 80%. Keep the distance above 20mm, and the infrared rays will not be transmitted into the camera.

  4. The heat dissipation pad on the bottom of the M1/M1w module needs to be connected to the largest possible copper skin to improve the heat dissipation performance

  5. The pads of white light lamp beads and infrared lamp beads need to be connected to the largest possible copper skin to improve heat dissipation performance

  6. The capacitor to the ground of the white light fill light should be removed, otherwise it will reset when the light is turned on

  7. If capacitive touch is needed, try to put the touch chip under the position close to the finger touch. Because of the trace length between the touch chip and the touch panel, the longer the length, the more difficult it is to grasp the sensitivity and the easier it is to be interfered.

  8. For each K210 module pin and power pin used, try to add ESD diodes. The location of the ESD diode is selected according to the actual situation

  9. If there is a requirement for certification, all data lines D0-D7 of the screen/camera and 4 control signals, as well as other communication signal lines, need to add RC filtering to eliminate overshoot and ringing according to the actual measurement conditions. The parameter is 100R+100PF (It is best to decide according to the actual test), low-pass RC form (the signal output first passes through the resistor and then the capacitor, and the RC component is placed close to the M1 module). Try to add RC filtering to other output signals (resistance and capacitance are determined according to the actual signal frequency)

  10. Try to connect 200R resistors and ESD diodes to each IO to protect the IO ports

  11. The working voltage and tolerance voltage of RST, BANK6/7, camera 8-bit data and screen 8-bit data of M1/M1w module are 1.8V, and the working voltage and tolerance voltage of BANK0/1/2/3/4/5 All are 3.3V withstand voltage, and must not exceed the withstand voltage range. If you want to use the RST pin, it is recommended to use a MOS tube to form a level conversion circuit.

  12. The 5V of the module is the input, and the external power supply is used for the module; the 1.8V and 3.3V of the module are generated by the internal DC-DC of the module, which are mainly used for the internal core components of the module, and secondly for the small current components outside the module. (For example, as a 1.8V reference voltage for screens and cameras, and other small current requirements. It is not recommended to provide large current components outside the module)

  13. If you use the M1w module, you need to follow the antenna placement principle to place the IPEX 2.4G antenna, otherwise the signal will have a greater degree of loss

  14. IO16 (BOOT) needs to add a 10K pull-up resistor to 3.3V on the bottom board

  15. FPIOA allows users to map 255 internal functions to 48 free IOs on the periphery of the chip