TSP5435X MOSFET selection

Amanda Ross95

Other Parts Discussed in Thread: TPS54352, TPS54356

Hello,

We're working with the TPS54356 (12V to 3.3V@3A) and the TPS54352 (12V to 1.2V@2.3A). I understand the EVM calls for the Si4888DY FET but I wanted to know if there would be any repercussions to using the Si4090DY (100VDS , higher drain current and Rdson). I know that the higher Rdson will lead to more power dissipation but is there any other reason this Si4090 FET would be problematic with either the TPS54352 or TPS54356? I realize this is more of a MOSFET question but they sort of correspond so I wanted to throw it out there anyways.

Thanks for your time,

-Amanda

over 7 years ago

0 JohnTucker over 7 years ago

TI__Guru**** 191445 points

We are going to use SI4386DY-T1-E3. Gate charge for Si4090DY is quite a bit higher.

0 Amanda Ross95 over 7 years ago in reply to JohnTucker

TI__Intellectual 2740 points

Hey John,

Thanks for your quick response. By referring to the SI4386DY, do you mean you're currently working on something with similar voltage rail requirements?

And so you're also saying that the Si4090 gate charge is too close for comfort?

-Amanda

0 JohnTucker over 7 years ago in reply to Amanda Ross95

TI__Guru**** 191445 points

The SI4386DY FET is the alternate we are choosing for the EVM. I'm not sure if the gate charge is too high or not. I just noticed that it is double what is spec'd for SI4386DY. I really have not used those parts much in the last 10 years or so. Questions about them come up very infrequently.

0 Amanda Ross95 over 7 years ago in reply to JohnTucker

TI__Intellectual 2740 points

Okidokey. Thanks John!

0 Amanda Ross95 over 7 years ago in reply to Amanda Ross95

TI__Intellectual 2740 points

Hey John,

One last thing if possible! The TPS54356EVM uses both a snubber and the HF decoupling caps. Which of these is most important? I know the snubber decreases ringing but wouldn't the decoupling caps help filter that out on the output as well?

Thanks for your help!
-Amanda

0 JohnTucker over 7 years ago in reply to Amanda Ross95

TI__Guru**** 191445 points

I designed that EVM back in 2004, so I do not remember the exact details. I think the snubber was need due to large overshoot on the SW node. I often add some extra high frequency bypass capacitors on the output. It all depends on your actual filtering requirements.

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TSP5435X MOSFET selection