Controller IC for DC/DC converter

Hi all,
I am designing a buck DC/DC converter, and I would like to do it with minimum number of components. I have been looking for a controller chip that provides 20V firing signal but what I found is many of them use 12v and sometimes 5V. First, my question is why 12V? I think 15V is better voltage to fire a Mosfet and I have been doing this for a long time (except logic level MOSFETs and GaN). my second question is do you familiar with a chip that provides 20V gate signal. 15V is ok, however, the loss will increase.

Thank you for your help.

Hi,

Please confirm: you are talking about gate drive voltage
I think this is development the wrong way round. In my eyes it makes no sense to start with gate drive voltage.

Start with your "real" requirements, like input voltage, output voltage load current, efficiency, switching frequency...

Indeed I see no benefit in driving a MOSFET gate higher than 12V or 15V.
For more detailed and more reliable informations I recommend to read datasheets of Mosfets and application notes about Mosfet gate drive design.

Modern MOSFETs are fully ON with V_GS of 7V. And the change in R_ds_on above this voltage is only marginal.
Thus driving with higher voltage than 12V makes not much sense.
On the other hand many MOSFETs specify the "absolute maximum voltage" with +/-20V. Any tiny overshot in time and voltage may harm the MOSFET. I don't know a single MOSFET where V_gs of 20V is specified as "recommended operation condition".
Don't risk early dying of the MOSFETs.

Increasing V_gs mainly increases the charge that is pushed into the gate....and exactly this charge needs to be dissipated when the MOSFET has to be switched OFF. This not only means increased gate drive power that will generate heat, it also means increased switching delay.

Klaus

Thank you for your response.
Actually, this is a 1500V to 200V 500W converter nonisolated. I find a chip that I can use to control this converter, not exactly what recommended in the datasheet but I think it can be utilized by some extra components like an extra small DC/DC converter to supply chip, etc. The utilized MOSFET is a SiC device which better to be fired by 18V~20V. I looked at Littlefuse made SiC 1700V Mosfet and there is large difference between RDSONs in 12v and 18V.
I don't like to add external gate drive to the circuit, but I think I must to.

There is no way you'll find a buck controller that can drive a 1500V half bridge. You'll almost certainly have to go with a fully isolated solution for that (special high voltage rated isolation too).

And for 1500V you'd want more margin than 1700V parts.

Thank you for the response,
1500V is with considering good safety margin. By old technology, on one Si die voltage was limited to 700V. But recently I have seen at more higher voltage like 1200V. IR2213 which is a nonisolated 1200V half-bridge driver may be a good example. I was wondering if some at higher voltages might be available and embedded in a converter controller.

UC3856N can drive a gate drive Tx ( ideally with buffers ) for running an half bridge to do your down conversion - 2 x 1700 V SiC - but not much margin if the input volts have a transient ... you can't use peak current mode with a half bridge though - so SG3524 might be a better choice ...