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How to enhance EFT ability in product development process?

To ensure the chip execute in normal state, in addition to IC noise filter function itself, hardware protection is also very important. Under normal circumstances, user should protect from the following aspects: 

  1. Power Supply: to ensure power supply stability, strong electric energy storage circuit cases, abnormal voltage protection circuit should be considered according to the situation. User must connect a small capacitor (recommended value is 0.1uF) in parallel between VDD and VSS, and the location must be correct, it must undergo a capacitor first and then reach the chip power supply.
  2. Reset port: if using external reset, please design the reset circuit in accordance with the proposed circuit; If using internal reset, in general, only connect Vdd with RST directly, or set the reset port as input port mode for use. If you require higher noise filter ability, you can pull up a 100K Ohm resistance to Vdd on RST port or the port can be set as input port, and there is no need to add a capacitor to ground on RST port, because the high frequency interference of power supply will directly invade chip through a capacitor. Also in reset circuit PCB layout, try to be as close to the reset pin as possible, thus to reduce the coupling strength on the side of power. 
  3. Crystal: when design oscillator circuit, user should choose an appropriate match capacitance corresponding to crystal parameters. In general, the capacitance value should not be too large when chip operating frequency is too high. In oscillator start-up and stops frequently required occasions, the capacitance value on XOUT side can be slightly larger than the capacitance on XIN side, even can parallel connect a large resistor R1 on both side. In addition, the oscillation circuit should be as close to chip oscillator pin as possible, and leaves adequate distance (3mm) to ground and power lines in order to avoid high-frequency noise. 
  4. I/O Port: for high noise load, it is better for user to isolate it with optocoupler components or add noise suction circuit, if there is dangerous load, user should add a pull-up or pull-down resistors to prevent malfunction when microcontroller damaged. Also, for security need in some special occasions, some dangerous load can also use software pulse-driven approach, through capacitive coupling, in order to avoid danger when micro-controller reset or the machine starts error.