ADuM6402 VDDL input pin connection

Q 

ADuM5402 has been replaced with ADuM6402 on PCB (due to component
availability). However, some parts work but others don't. Datasheet says VDDL
pin on ADuM6402 must be connected. What happens if this pin is left open (as in
case of ADuM5402)? Also, would be there be any difference in behavior in a
system powered by 5V or 3V with VDDL pin left open?

please advise





Document IconViso Startup Issues Rev A.pdf Type: application/pdf
Name: Viso Startup Issues Rev A.pdf
- Viso Startup Issues Rev A.pdf


Document IconViso Startup Issues Rev A.pdf Type: application/pdf
Name: Viso Startup Issues Rev A.pdf
- Viso Startup Issues Rev A.pdf

 

A 

There are several things that can cause problems in the isoPower series.

We had a startup issue with the original silicon of the isoPower parts -> it
has symptoms of power either not coming up at all, or coming up to an incorrect
regulation point. The last part to switch to the new silicon was the ADum640x,
so the older silicon is still available in distribution.

The ADuM640x also split the power supply to reduce internal noise, but there
are still some internal connections which can parasitically power the data
channels from the isoPower. It is required to provide power to Pin 7 for
reliable operation of the data channels. But it may operate in an unstable mode
if the pin is left open. Bypass is important on this pin as well. A jumper wire
to pin 1 may be acceptable, if it is as short as possible and something the
gage of wire wrap wire.

There may be a difference in data channel behavior as a function of voltage,
since parasitic power tends to come in through diodes, it drops the voltage
further internally. It also probably makes a difference what the data channels
are doing, since that is another path for parasitic power.