To whom may it concern,
Hi i'm HS.
I'm posting this in order to ask several questions about aux power and ground and miscellaneous things.
Q1. LT4293 needs Isolated DCDC, such as Flyback, Forward as well as ideal bridge diode and its controller(LT4321)
I would appreciate if you provide me with how the grounds should be connected to each blocks.
I assume LT4293 should be connected to primary ground tho.. i would appreciate if you clarify which point should be divided into three different grounds(Chassis, Primary, Secondary ground)
Q2. I will populate the DC Jack as well as PoE as power input like the diagram below.
Q2-1. Would you recommend me proper choke filter(coil) for LT4293?
I used LT4295 in my application before and the datasheet recommended a choke filter for LT4295.
But i couldn't find recommendation for choke filter for LT4293.
Q2-2. In my application, The priority of DC JACK should be higher than PoE, which means PoE should be shut down when the dc adapter is connected.
Also, i think output of DC adapter doesn't need to go through the isolated DCDC when the DC adapter is connected because it will cause the power loss for nothing since output voltage of both dc jack and isolated DCDC is 12V.
I read the datasheet of LT4293 and found out that LT4293 can be shut down by the voltage of AUX pin of LT4293 with two voltage divider resistors.
As you see the simplified power diagram of my application, DC jack output should be connected to AUX pin of LT4293 in order to shut down the device, but the problem is that the ground of DC jack should be on primary side while end point DCDC/LDO is on secondary side.
Is there any way to shut down the LT4293 and bypass the isolated DCDC when the dc adapater is connected?
Or would you verify if there is no much of power loss going through isolated DCDC from 12V(primary) to 12V(secondary)?
Q3. Is there any layout guide for LT4293 with respect to Isolated DCDC and LT4321?