Usage of 2 DC/DCs - why?
markusdd opened this issue · 6 comments
Hi, I have on simple question: The ISO variant uses 2 DC DCs in series:
Why is this being done? I would have assumed that just using an isolating DC/DC module like WRB4805S-3WR2 should work?
What am I missing?
WRB4805S-3WR2 doesn't seem to have enable pin.
Basically there is suggested hardware setup when you use TPS2375PW.
Understood, but still it seems to be kind of twice the hardware. And also efficiency loss because you go through 2 DC/DCs.
If the isolating DC/DCs lack an enable couldn't this be done by using a simple low-RDS_on FET t turn it off when not needed?
Also: What is the point of enable? If there is no vooltage coming out f the ethernet jack?
Enable is connected to TPS2375PW's PG pin. What is TPS2375PW's PG pin? It is explained in this document: https://www.ti.com/lit/ds/symlink/tps2375.pdf
Also twice the hardware is not always bad thing if it is four times lower the price or reduces heat over a component.
That is true, but the reason I am asking is because the current isolating DC/DC is not goood enough for the platfoorm I am targeting an I am looking into designing something that can drive more than 400mA at 5V.
Looking at isolating DC/DCs that manage 600mA up to even 1200mA, at 78% or even more efficiency, so I am not sure which benefit the extra DC/DC brings except more cost, area and moore external components.
I understand but unfortunately ESP32-POE-ISO design is not suitable to for such loads. Maybe consider ESP32-POE, it is not isolated design but allows double the wattage: https://www.olimex.com/Products/IoT/ESP32/ESP32-POE/open-source-hardware
I guess I have to come up with something myself because isolation is a must for my applicatioon.