I have a working SI3402 non-isolated setup (Eval board and/or my board, same setup).

I noticed that relative to ground, that the 5V rail is actually 48v above POE "ground", and the output ground is 43v above POE ground.  Okay so that's 5v, great!

So if I power my device, and hook up that device to may laptop via USB, is it going to blow up my laptop?

So I figured, if my laptop was disconnected from everything and floating, then no issue.

But what if I charge from AC?  Well that charger is isolated (I hope) so still no issue?

What if I attach to an HDMI Monitor? Well that HDMI Monitor is also powered by an isolated transformer (I hope).  So we're still floating.

Well.. what if I hooked up the device to some other silly product that had a AC 220V-DC capacitive dropper (non-iso), well.. then hopefully my POE switch has an isolated AC/DC Transformer.

So I can't think of the exact situation where this non-isolated power is going to blow stuff up.... Is there any warning you can share?  

For the most part, USB is used only for my development purposes (USB-Serial) so in actual application, there is no consumer facing port.  So I'm mostly concerned about safety of my personal equipment.

I wanted to check if there was a typo in the reference design Si3402BISO-EVB

For 5v output, coilcraft designates FA2805-CL* as the output transformer.

https://kr.mouser.com/datasheet/2/597/fa2805-463392.pdf

 

However in the design document for the Si3402BISO-EVB, "Table 2. Component Selection for other Output Voltages and Filter Types" it specifies  FA2924CL which does NOT EXIST.  There is only a "FA2924-AL" or a "FA2805-CL"

https://www.silabs.com/documents/public/user-guides/Si3402BISO-EVB.pdf

Shall I simply run with the 5v transformer FA2805-CL?

Thanks!

Hi,

I need to supply my electronic device with any PSE, so i have desinged my board with SI-3404 according to SI-3404-EVB board schematic (page-45). But when i connect my board to PSE, my SI-3404 board does not give any output (i wish that it gives 24V output when i plug it to PSE). My board schecmatic is below, so ,what is the difference between EVB board and my board? Any advises ?

Hi,

I need to supply my electronic device with any PSE, so i have desinged my board with SI-3404 according to SI-3404-EVB board schematic (page-45). But when i connect my board to PSE, my SI-3404 board does not give any output (i wish that it gives 24V output when i plug it to PSE). My board schecmatic is below, so ,what is the difference between EVB board and my board? Any advises ?

Is there any reference material for designing a Si3404 isolated flyback converter that outputs 24V as a class 3 PD? If not, can you point me in the direction of how I might calculate the requirements for one?

Hello, 

We used the Si3402-B to design an isolated PoE Converter with 12V output. Unfortunately we have some EMI overshoots with this setup in the conducted and the radiated frequency band:

• Conducted EMI (150kHz - 30Mhz): biggest overshoot at ~375kHz (near the 350 kHz switching frequency of the coverter)
• Radiated EMI (30Mhz - 1Ghz): Wideband (plus-minus 10Mhz) noise around 165 Mhz.

We followed the reference design explained in the document SI3402BISO-EVB and used the specified values for 12V output in Table 2. But for the big input and output capacitors we decided to use Ulta-Low-ESR polymer aluminum electrolytic capacitors.

• Input capacitor: 12µF, 25mΩ ESR
• Output capacitor: 330µF, 20mΩ ESR

At point "e" of the design planning checklist on page 11 we found the following statement:

"... using a low ESR filter capacitor ... requires some recompensation of the feedback loop. Silicon Laboratories recommends against component substitution in the filtering and feedback path as this may result in unstable operation"

Do you think that the capacitors could be a problem?  If so, could you give us a hint how to adjust the feeback loop compensation?

Best regards

Janis Sarikas

Hello,

we would like to use the Si3402-B as a 48V to 12V isolated converter via 48V power supply only. That means we don't need PoE on the input side.

Is it possible to put the pins CT1, CT2, SP1 and SP2 simply to ground or leave them unconnected in this situation?

Backround: We already use the Si3402-B for an isolated PoE splitter in one of our projects. In new project we want to design a "PLC (Power line communication) splitter" with more or less the same dimensional and electrical requirements. Therefore we would like to reuse design from PoE splitter project regarding the isolated 48V to 12V conversion.  

Best regards

Janis Sarikas

Hi,

I would like to simulate the class 3 5V PD DC/DC design I have however I am struggling to understand what the gain of the device is from EROUT to the FET current.  From the datasheet it implies that the EROUT amp has a transconductance of 50uS and that the FET current monitor has a divisor of 1072 however I can't seem to make that work.  I am out by a factor of 10.

Can you please confirm the gain that the device adds to the loop so I can simulate.  FYI, I am using the Ridley Engineering Power-123 simulator if you are familiar with this.

Thanks...

Graeme

HI,

I am currently designing a 5V class 3 PD with the Si3404 and have selected the WE transformer 750313082.  Despite have a low value i=of primary inductance (37uH) necessitating a higher clock frequency the primary selection criteria was the primary current rating of 3amps.  This sits well with the worst case Si304 FET current of 2.7A.

I noted in a recent post that you are updating some reference designs to also use WE transformers and the 5V part you recommended is the WE 749119950.  When I reviewed this and the other parts you recommended  parts I found that the primary current was between 1.4 and 1.7A.  This is significantly below the worst case Si304 FET current of 2.7A.  Won't these transformers saturate or am I missing something?  Are you limiting the power to ensure the current remains under the max recommended by WE?

Can you share the new WE reference design you have created?

Thanks....

Graeme

Hi,

I noticed that the Si3402-C is marked as NRND at Digi-Key. Is this correct? It's still listed as active at Mouser.

I'm looking at a new low power isolated flyback POE PD application, and the Si3402-C seems to suit well - if I can buy it now and into the future.

I could use the Si3402-B, however that part seems to have not had the ESD respin mentioned in Bulletin #1610181, "Si3402-B and Si3402-C Human Body Model ESD Notification" from 2016.

Is the Si3402-C supported, and will continue being sold by distributors, and likely to be for the next 5-10 years? Or should I be using the newer Si3406-A?

Thanks,
Brian

Hi, is there got a configuration sequence to force turn on a port of Si3454? I mean if I can turn on a port even when there is no PD device is connected.

Hello,

I just received my eval board for the SI34061. However, UG333 references board version 1.0, and I have received board version 1.2.
The BOMs and schematic don't match, so any modifications are extremely hard to make.
Where could I get a hold of the new UG333 with updated schematic and BOM?

Thank you very much!
ML

Hello

I'm wanting to change the 5v EVK output voltage of the si34061(UG333 : Class 4 Isolated Evaluation Board) to 12V.

Consulting AN1130 I found section 5.10.3 that referes to the equation VOUT = 1.24V*(1 + R1/ R2).

So all I need to do is change R1 and R2?

Thanks

Hello,

I'm planning to use the Si3404 for a 12v/7W output (ISO-FB), and due to max height constraints I'm ending with a (really) short-list of transformers...

Actually only Wurth's 7491192912 with 7,4mm Height seems to physically fit, although I'm not sure for electrical parameters, hence my question:

Will this guy do the job ? : L:210uH / Lleak:2.5uH / RDCpri:630mOhm / RDCsec:100mOhm

P.S:Aux voltage is only 10V so I assume I won't be able to use it for V15 ? ...

Thanks for your time,

Laurent

Hello,

I would  like to use the SI3404 to achieve 5V/1A in output

I can't find the same transformer as the transformer on the SI3404 démoboard (Mentech)

I see on an other post that you you advise the FA2924-AL whereas in the datasheet it said, the output delivers 3.3V:

FA2924-AL_	40.0	36.0	0.100	0.025	0.666	1 : 0.3	2.0	3.3 V, 4.5 A
FA2805-CL_	40.0	36.0	0.108	0.040	0.621	1 : 0.4	2.0	5.0 V, 3.0 A

Is the FA2805-CL a good transformer for 5V ? 
IS the 2924-AL can be used too for 5V ?  (and Why ? )

Any help would be great.
Thank you