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The usage of ADuM3221

Hi, Everyone.

I use two  ADuM3221 to driver a Synchronous Buck(I choose ADuM3221 becuase application requests the operation temperature -55℃~+125℃), whlie each ADuM3221 is connected to one mosfet. Both ADuM3221's Pin 3 and Pin 6 are vacant. I provide a isolated +12V power source between VDD2 and GND2 to drive the high side mosfet but not a bootstrap capacitor. And the GND2 is connected to the Source of high side mosfet.

Other connection are the same as Typical Connection in the datasheet. And the gate resistor paralled with a fast swithing diode is 5R. Schematic shows below.

When the input of the Synchronous Buck Vin on, the waveforms of VGS are all fluctuating (about 1V). Waveform shows below.

Q1. If I only use one channle of ADuM3221, how deal with the unused channel?

Q2. How to solve this problem?

Hope to get prompt reply.