Dusl synchronous buck controller with higher gate drive voltage?

[Flyback]

Hello,
We are using a LTC3890 dual synchronous buck controller to do a 48v to 13v3 buck converter with 20A output. The LTC3890 only has a 5V FET drive which is too low to properly enhance the gates of the FETs we’re using
Does anyone know of a chip similar to LTC3890 but with higher gate drive voltage?
The LTC3890 means we need to choose FETs with rdson specs down to 4.5V, and very few FETs with 60v capability have this.

 

[spec]

Hy Flyback,

Would you be happy if you could get a MOSFET with a low RDSS at 4V5 gate drive?

If so, presumably you are after an NMOSFET. What RDSS would you call low? How much drain current do you need?

spec

 

[Flyback]

would like a i milliohm nfet with vds 40v. And Qg <32mQ if poss.
Will have to write to santa i think because there arent many like this.

 

[ronsimpson]

vds 40v

Voltage D to S 40V ?
------------------------
There are many 0.003 ohm 60V 100A parts.
------------------------
sorry, I see it says DS but I read GS. (not seeing well today)

 

[Flyback]

yes, off state voltage withstand to 40v vds.

 

[spec]

would like a i milliohm nfet with vds 40v. And Qg <32mQ if poss.
Will have to write to santa i think because there arent many like this.

Hmm 1 milli Ohm. Can I ask why. Isn't the connecting wire/PCCT going to be higher than that? Intriguing
What peak IDS do you need?
Any idea of power dissipation?

spec

PS: where are you?

 

[ronsimpson]

Hmm 1 milli Ohm. Can I ask why.

I agree that seems like a BIG mosfet.
20A 0.001 ohms 20mV. Sounds like the AC loss will be higher than the DC losses. If you are switching fast I think a smaller MOSFET might have lower losses. (AC+DC)

 

[spec]

Hy Flyback,

Here are the NMOSFETs I have come up with so far:

(1) Infinion (International Rectifier) BSC010N04LS (where do they get these numbers from )
VDS: 40V
ID: 100A
Rdss: 1mR @ 4.5VGS @ 20A
QGtot: 50nC @ 4.5VGS & 20AID (extrapolated from graph #14 in data sheet)
Ptot: 139W @ Tcase=25C
RthJC: 900mDCW
Pack: PG-TDSON
Data Sheet: https://www.infineon.com/dgdl/Infineon-BSC010N04LS-DS-v02_00-en.pdf?fileId=db3a3043353fdc16013552c1c63647c4
Cost: £1.60UK (Mouser)

(2) ON Semicinductor NTMFS5C404NL
VDS: 40V
ID: 370A
Rdss: 870uR @ 4.5VGS @ 20A (Extrapolated from Table#4 in data sheet)
QCtot: 80nC @ 4.5VGS (Figure 8 in data sheet)
Ptot: 167W @ Tcase=25C
RthJC: 750mDCW
Pack: SO-8FL
Data Sheet: https://www.onsemi.com/pub_link/Collateral/NTMFS5C404NL-D.PDF
Cost: £1.34UK (Mouser)

(3) Fairchild FDB016N04AL7
VDS: 40V
ID: 306A
Rdss: 1.3mR @ 4.5VGS @ 20A (Extrapolated from Figure #3 on data sheet)
QCtot: 50nC @ 4.5VGS (Extrapolated from Table #6 in data sheet)
Ptot: 283W @ Tcase=25C
RthJC: 530mDCW
Pack: TO-263
Data Sheet: https://www.fairchildsemi.com/datasheets/FD/FDB016N04AL7.pdf
Cost: £2.99UK (Mouser)

(4) Texas Instruments CSDI8509Q5B
VDS: 40V
ID: 100A
Rdss: 1.25mR @ 4.5VGS @ 20A (extrapolated from graph in data sheet)
QCtot: 68nC @ 4.5VGS (extrapolated from graph in data sheet)
Ptot: 195W @ Tcase=25C
RthJC: 800mCW
Pack: Q5B
Data Sheet: https://www.ti.com/lit/ds/symlink/csd18509q5b.pdf
Cost: £1.91UK (Mouser)

 

[simonbramble]

LTC3892 - it was designed to be a replacement for the LTC3890 in applications that need a higher output voltage and generally more grunt (so you need higher powered FETs with bigger VGSs)

and there is an LTspice jig file for it too

Hope this helps

Simon

 

[simonbramble]

for the top FET you need to balance RDSON with QG. Go on to Vishay's website and download all the NFETs into Excel. then construct a column of QG (at the appropriate gate drive voltage) x RDSON (at that same gate drive). This will give you an idea of the Figure of Merit of the FET. Pick the FET with the lowest Figure of Merit. Obviously delete the parts that dont meet your VDS or ID specs. This is your top FET. For the bottom FET, pick the one with the lowest RDSON. You don't want the lowest RDSon for the top FET

 

[Flyback]

Thanks SimonBramble, BTW, may i ask, do you know in which version of Excel the "LTCXXXX family power design tool" is used in? They want us to fill one in for each design, but it wont seem to open in my Excel 97-2003.
It opens but has gobbldegook characters, i definetely saw it open and cosha in the latest version of excel.

 

[simonbramble]

Use LTPowerCAD instead. It has got much more functionality and is much more user friendly. You can download it from linear.com

 

[simonbramble]

https://www.linear.com/designtools/software/#LTPower

 

[simonbramble]

... also, at that sort of current, the PowerPAKSO8 package is probably the best one to use. No leads so little inductance so little ringing at the switch node. Good thermal bonding to the PCB too