ESD protection problem

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ESD protection problem

Contributor III

mcu:                     8bit    MC9S08SC4

function :             dc motor control      current about 1A

the shell:             PCB ground and Motor negative connected with the metal casing directly,Half of the shell is                               metal  half plastic

phenomenon:   1:  when +15kv air dischage at the metal shell,the mcu reset.    distance between the discharge                                  point and mcu is about 6cm.

                            2:  solder a wire on the metal shell.  Hung it above  the mcu about 3cm.  then +15kv air discharge                                  at the wire,the mcu  breakdown.

breakdown mcu phenomenon:

                              I use a LDO to supply the mcu power;normally the voltage should be 5v, because of the                               breakdown mcu,it is 1v.    if I replace the old with new one,the LDO voltage  return to normal 5v.

operation procedure:1:bring generator electrode close to the discharge point  until 3mm ,then switch on ,arc appears .

                                  2:the devece is  placed  on the horizontal coupling plane directly.

help1:  operation procedure is correct?

help2:  layout suggestion to prevent ESD damage to the mcu.Especially radiated interference.the specific circuit design is              much  needed for a newcomer.

thank you for your read and help!


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