Dear TI Experts,
What is the use of Q7 and Q8 totem pole driver stage in PMP5711 ?. UCC2897A already having 2A source and sink capacity.
Regards
Aneesh
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Hi Aneesh,
You are right, the UCC2897A has 2A sink/source drivers. The NPN/PNP are used for current amplification to drive the parallel NFETs. The designer of PMP5711 is traveling this week. He can provide a more detailed response when he returns.
Thanks,
Ryan
Hello Aneesh,
we're not talking on continuous current here; the driver just provides peak currents around Miller plateau.
Here you have to regard current gain beta of BJT. Just check test report page 9, figure 10/11,
so Vds and Vgs of primary FETs - do you like the waveforms ?
If there would be sth. wrong at the control of the FETs you won't meet the 94%.
And YES, BJT could work at even higher frequencies; almost 40 years ago I built some SMPS w/ BJT's;
there has been less FETs on the market, started w/ BUZ11 - but at much lower Fsw used as power switch...
Best regards, Bernd
Hello Aneesh,
if you don't like the BJT PP just use i.e. UCC27517,
a dedicated FET driver - powerful, but in a tiny package.
Place this driver close to the gates.
Best regards, Bernd