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Bootstrap high side drive controller/sync rect controller combo?

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cupoftea

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Hi,
Do you agree, that LT1681/LTC1968 combo cannot serve a spec of….

150VDC in
30Vout
400w = Pout
2 Tran Forward with synchronous rects.
External Bootstrap driver capable of 200V.

...This is because even if a high side bootstrap driver chip capable of the 200V were used, and fed from the hi-side drive bit of LT1681, its turn on/off propagation delay would be too slow, and the sync rects would end up getting turned ON before the primary upper FET got turned ON?

However, the combo could still be used if the high side FET were driven via a pulse transformer, which woudl be faster than a 200V bootstrapper?

Do you agree?

I am baffled why the datasheets of such low voltage 2 Tran forward controllers like LT1681/LT3781/LTC3723 don’t recommend a high side pulse transformer drive to extend the Vin range of the chip?......is it that they just don’t care about sales?

I mean, the mentioned controllers are superb in that they also control the secondary side sync rect controller (LT1698 or LTC3901). This saves the designer from the multiple perils of “reactive type” sync rect drivers, which have no communication with the primary side whatsoever. Eg NCP4303…the NCP4303 has a "compensatory inductance" connection which is good….but shows the difficulty that all such type of sync rect drivers face (not knocking the NCP4303…at least it “owns up” that these chips suffer badly from stray inductance effects, unlike the ones that communicate with the pri side controller)

LT1681
https://www.analog.com/media/en/technical-documentation/data-sheets/1681f.pdf

LTC1698
 

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