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AD8221 Diode Clamp Input Current

Question asked by jake65892 on Jun 7, 2012
Latest reply on Jun 7, 2012 by harryh

The AD8221 states in the datasheet that it meets HBM up to 1kV and that the inputs can withstand up to 6mA of constant current (see Input Protection section on page 19 of the datasheet).

 

Because the diodes can withstand 6mA of constant current, I am assuming that they can withstand much more current for shorter periods of time.  I would like to get an idea of how much current these diodes can dissipate for my transient pulse.

 

Since the current rating is really a function of how much power the diodes can dissipate before they heat up to a certain temperature, the rating is more of a power/energy than a current (although power is easily calculated from current since the diode drop is usually around 0.7V).  The datasheet says they can withstand the HBM up to 1kV, and therefore should be able to withstand an energy of 50 uCoulombs (using 100pF, 1000V, and the formula Energy = 1/2*C*V^2).

 

If these same diodes were hit with a 32.3mA pulse for 1us (conveniently, the transient pulse which I am trying to withstand), assuming they were 0.7V, the energy dissipated (using Energy = Power * time, where Power = 33.2mA * 0.7V) would be 22.61 nCoulombs, or 0.02261 uCoulombs, much less than the energy in an ESD strike.

 

Is this a safe assumption?  If not, is there a better assumption or rating that I should be using for these diodes? 

The real question is, will these diodes withstand a 32.3mA pulse for 1us?

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