HITEQUEST
technical interviews for high-tech professionals

 
 
 

 

 

   

 =BRAIN STORM= 

 

 

  • burnin board problem... by releng.
    I run reliability tests in burnin chamber. My board is populated with over 20 semiconductor parts switching at full rail. The switching generates over and under shoots which, I think, may affect the life time of the parts. What is the best way to handle this? Also people use different terms, such as "ringing", "overshoots", "spikes" - are we talking about the same effect?

     
     
  • rel guy
    I have been facing similar problems with my switching circuits. I would suggest to try bidirectional TVS - transient-voltage-suppression diode. It works pretty much as zener diode, clamps voltage once it reaches the specified value.
         
     
     
  • Chiy Ping
    Is the nature of the ringing effect capacitive of inductive? Or both? thanks.
     
     
  • a.m
    The ringing effects are due to both inductive and capacitive parasitics in the circuitry.
    The peak voltage swing is defined by equation: V = LdI/dt
    If rising and falling time during switching is not an issue I would use current limiting resistor to reduce overshoots.
    The resistor should be non inductive, for example carbon composition type or carbon film resistor. Avoid wire wound type as it is inductive.

     
     

  • Burnin boards have usually large size and long traces.
    On the long traces Impedance mismatch can result in ringing – oscillatory behavior from excess inductance.
    Transmission line termination at source or receiver should help.