ADuM4169:  Powering VBUS1 from 5V and VBUS2 from 3.3V.

Document created by analog-archivist Employee on Feb 23, 2016
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I am looking at using the ADUM4160 USB Digital Isolator powering the input
VBUS1 side from the 5V computer input but the VBUS2 side from 3V3. Looking at
the datasheet it would appear that the voltage range is 4.5-5.5V so the VBUS2
voltage would be to low. I have now looked at your circuit Note CN-0160 and
this states on page 3 that the VBUS inputs can be powered from 3V3 rails. Can
you confirm that this is correct and do I connect both the VBUS2 & VDD2 inputs
to the 3V3 rail.

 

Page 3 states that:  "Power can be provided as 5 V through the VBUSx pins, and
the 3.3 V signaling voltage is created by an internal 3.3 V regulator at the
VDDx pin. Alternatively, the 3.3 V power can also be provided to VBUSx and
VDDx, and the part uses the external supply directly, disabling the internal
regulator".

So you have a choice to apply 5V to Vbusx pin and allow the internal regulator
to generate the 3.3V at Vddx OR the other option is to run the downstream side
from a single supply, the Vbus2 and Vdd2 can be connected together bypassing
the internal LDO and 3.3V can be provided to both pins.
Note, the actual circuit in CN-0160 is connected to 5V as in that case we are
using the internal regulators, if we did not need to use the internal
regulators, we could have bypassed then by connecting Vbus 2 and Vdd2 together
to 3.3V.

Page 3 also explains the reason for providing these two options: " to allow the
ADuM4160 to run either from a 5 V USB cable or from an available 5 V or 3.3 V
rail supplied by a peripheral".

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