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AD8318 followed by AD8138

Question asked by sncdan on Jul 23, 2018
Latest reply on Jul 23, 2018 by JinoL

I have an AD8318 Log Detector followed by an AD8138 Differential Driver.  The log detector is behaving correctly, as VOUT goes between 0.8-4.0VDC over the dynamic range of the input RF signal.  However, the AD8138 used to translate from single-ended to a differential voltage output remains stuck at a +5.3V differential.  The +OUT pin is at +3.4V to ground, the -OUT is at -1.9V to ground, or +5.3V from +OUT to -OUT.

 

The AD8138 power supplies look good at +5V and -5V respectively.  The only strange thing is that it takes ~15 seconds for the -5V rail to come up after the +5V.

 

Schematic is attached.  Any ideas on what might be the reason for the AD8138 to be stuck?

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