Feasibility of a small custom 1W SMT DCDC transformer for qty 1000

[PCB.Wiz]

Is the Skyworks SI8751 actually useful for fast gate switching? I'm switching <200A split across 4 fets (DC load switch)
Looking at the datasheet, GATE On Impedance is 162k  and output voltage 10V.
Am I correct in assuming that using a SI8751 is equivalent to applying 10V to a FET gate through a 162k resistor ?

Depends what you mean by fast 
They spec 85us typ to 90% (9.72V into 100pF)

What is the gate capacitance of the FETS you use now ?  Do you need 10V gate drive ?
What isolation do you need from control side, and between units ?

I see TI have a nifty looking  UCC33420 PREVIEW  1ku  $1.300  in a 5x4x1mm SMD package.
5V/5V 1.5W 3kVrms isolated DC-DC module with integrated transformer

- not yet spec'd in higher voltages, tho they do older/larger models in higher voltages.

[Psi]

Plenty of similar isolated DC-DCs at LCSC for under a dollar :
https://www.lcsc.com/products/Power-Modules_634.html

You raise a good point.  Those are cheaper than what i'm paying.
However one of the reasons I want to replace these is they're SIP modules and I'm not entirely happy about the way they mount to the PCB in a line. They can wobble from side to side if pushed a bit.

[Psi]

Is the Skyworks SI8751 actually useful for fast gate switching? I'm switching <200A split across 4 fets (DC load switch)
Looking at the datasheet, GATE On Impedance is 162k  and output voltage 10V.
Am I correct in assuming that using a SI8751 is equivalent to applying 10V to a FET gate through a 162k resistor ?

Depends what you mean by fast 
They spec 85us typ to 90% (9.72V into 100pF)

What is the gate capacitance of the FETS you use now ?  Do you need 10V gate drive ?
What isolation do you need from control side, and between units ?

I see TI have a nifty looking  UCC33420 PREVIEW  1ku  $1.300  in a 5x4x1mm SMD package.
5V/5V 1.5W 3kVrms isolated DC-DC module with integrated transformer

- not yet spec'd in higher voltages, tho they do older/larger models in higher voltages.

Yes, need 10V gate charge for 1mR Rds
Everything is just 12V so don't need any serious isolation at all.

There are 4 fets in parallel, so 28nF

TPH1R204PL1
Input capacitance 7200pF
Total gate charge = 74 nC (typ.)
Gate-source charge = 16 nC
Gate-drain charge = 17 nC
Gate switch charge =  17 nC
Output charge =56 nC

[voltsandjolts]

How much do your DCDC converters cost?
I see Mornsun have +15V/-9V DCDCs for IGBT gate drives at around GBP3.50
https://www.digikey.co.uk/en/products/detail/mornsun-america-llc/QA153-1509R3/16643920

Plenty of similar isolated DC-DCs at LCSC for under a dollar :
https://www.lcsc.com/products/Power-Modules_634.html

Sure, lots of jellybean DCDC for $1 but I was specifically looking for isolated with reinforced isolation, high CMTI and low coupling capacitance from one of the few cheap chinese DCDC brands that I have moderate trust in. That's not a $1 part. But seems like jellybean might be OK here, given low voltage.

[Wolfram]

How much do your DCDC converters cost?
I see Mornsun have +15V/-9V DCDCs for IGBT gate drives at around GBP3.50
https://www.digikey.co.uk/en/products/detail/mornsun-america-llc/QA153-1509R3/16643920

Plenty of similar isolated DC-DCs at LCSC for under a dollar :
https://www.lcsc.com/products/Power-Modules_634.html

They do, but not with the isolation voltage (5000 VAC), isolation capacitance (3.5 pF) or characterized CMTI behavior (200 V/ns) of the QAxx3 series. Practically, it's not going to matter much if this application doesn't switch super fast, but even plain superjunction FETs at higher voltage can make enough dV/dt to cause trouble with improperly selected DC/DCs. 200 A suggests a lower voltage application where dV/dt won't be a worry, but it's something to keep in mind.

Note that LCSC list a range of converters with part numbers and specs identical to the Mornsun QA-series parts, and these are not meeting the specification at all. I tore down units from all the brands they list, and they were all done with plain magnet wire overwind and 30-ish pF isolation capacitance, compared to the double TIW and 3.5 pF of the original. Parts listed at Mornsun on LCSC should be the real deal.