BQ25756: Voltage rating of MOSFETs

Lary Cotten

Part Number: BQ25756

Tool/software:

I've got a design in progress using the BQ25856. To date, I was expecting 12-24V on the input side and 15-18V on the output side. In this particular case, the supply will only be used in forward mode, never in reverse to get power back from the output side. All my FET's are 40V FETs. Now I've been asked to support 48V input, but still have the 15-18V output. I found the 80V version of my FETs. My first thought is that I only need to change out the input side FET's for the higher voltage. Because this is a last minute change, I'd like a bit of confirmation so I don't mess it up. It seems so obvious that I have to ask.

4 months ago

0 Lary Cotten 4 months ago

Prodigy 120 points

A note about the design calculator spreadsheet "BQ25756_DESIGN-CALC":The custom MOSFET section at row 115 refers to Buck MOSFETs Q1 and Q2, then at row 133 it refers to Boost MOSFETs Q1 and Q2, same refdes as the buck MOSFETs. The schematic diagram at the top of the design calc doesn't label the MOSFETs at all.

0 Ethan Galloway 4 months ago in reply to Lary Cotten

TI__Mastermind 31400 points

Hello Lary,

Yes, it should be fine using different MOSFETs for the buck phase and the boost phase.

Let me know if you have any questions about this.

Best Regards,
Ethan Galloway

0 Lary Cotten 4 months ago in reply to Ethan Galloway

Prodigy 120 points

That answered my immediate question. Thanks. Our design actually has two different instances of this part, serving two slightly different functions. I could use a brief offline discussion to make sure we're on the right track.

0 Ethan Galloway 4 months ago in reply to Lary Cotten

TI__Mastermind 31400 points

Hello Lary,

I don't quite have time for offline discussion. If you send me your system requirements and setup, I can review the setup to make sure you are on the right track. We can discuss this with the E2E private message if you need to.

I can also review your schematic and PCB layout as well.

Best Regards,
Ethan Galloway

0 Lary Cotten 4 months ago in reply to Ethan Galloway

Prodigy 120 points

Does the BQ25858/BQ25858B have it's own design calc spreadsheet, or do I just use the same one I used for he BQ25856?

0 Ethan Galloway 4 months ago in reply to Lary Cotten

TI__Mastermind 31400 points

Hello Lary,

The design calculator for the BQ25856 will also work for the BQ25858 ICs.

Let me know if you have any questions about this.

Best Regards,
Ethan Galloway

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BQ25756: Voltage rating of MOSFETs