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AD8361 failures

Question asked by wa2pyx on Apr 18, 2011
Latest reply on Apr 21, 2011 by wa2pyx

I have a puzzling situation with the AD8361ART (the 6 pin version).  I had 3 in a row fail as nearly instantly as I can tell - that is as soon as I power up the board, the AD8361 is dead.  The failure is exhibited by the Vrms pin going to +3.2V even with no RF input.  the supply is 3.3V. Pdwn (pin 4) is connectd to ground. Fltr (pin 1) is connected to a 100 pF (other side of capacitor  to +3.3V).  Vrms (pin 1) is connected to a 100 pF to ground and to a National Semi ADC (ADC084S051).  ADC datasheet says maximum 1 uA input current.  ADC appears functional, i.e. it returns reasonable values when input is provided with AD8361 removed.  After the first 2 failures, I thought maybe I had excessive RF going into it, so I removed the input capacitor, so pin 5 (RF in) is returned to ground through a 75 Ohm resistor. I then installed the third AD8361, but it failed immediately as well.  The AD8361 is bypassed with 2x100nF ceramic chip capacitors and a 100 pf ceramic chip capacitor.  Checked the supply voltage, it is 3.3V.

 

Any ideas as to what I may be doing wrong?  So far all AD parts I've used have worked "as advertised".  So I expect the AD8361 will also, once I find & correct whatever is wrong.

 

I checked the top code -- it is J3A so I'm pretty sure the part is right.

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