I drive 3 FETs, so that would be one package per FET. I would like to drive them all from a single IC, 3 pcs is too expensive.
That is a good one, similar to the other ones I found, equivalent resistance of about 17 ohms, but about 3 times to high
I have looked into analog switches, which comes down in the numbers needed, but then the manufacturer knows well that he can ask for a higher price :-(
But an analog switch can only drive in one direction, so you'd need two per MOSFET. Expensive.
Paralleling two 'AC14 sections and driving both with a third 'AC14 section would get you two drivers per 'AC14 package.
An octal buffer part (e.g. the 'AC240) would get you three drivers. But, in this service, do you really *want* three drivers talking to each other over a common bond wire to ground?
Oh dear, an octal is one gate shy. Scratch that. But you could use an octal, make two drivers with six gates, and the last driver with one external buffer e.g.,
You must be driving giant fets. The NL37WZ16 rise time, unloaded, is about 700 ps. Driving the just-right-size fet, you can switch 50 volts at 1 amp in about a nanosecond.
Of course, our products are lowish quantity, and parts cost doesn't usually matter much. I sometimes use two or even three of the tiny triples in parallel (like, 9 gates!) to drive a mosfet.
"Anything worth doing is worth overdoing."
- Meat Loaf
The USB switches are fairly cheap and just a few ohms.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
You could at least try a permanently-enabled NC7SZ125 TinyLogic 3-state line driver (or its TI equivalent SN74LVC1G125).
The datasheet does not say much, but my experience with them so far is, that they are considerably "beefier" than other typical logic outputs. If accidentally driven against a 3.3V CPU or FPGA output pin, it would easily overdrive the CPU / FPGA pin strongly enough to land at a valid opposite logic level. The only indication that something is wrong apart from the other chip not being made to stand this for very long, was a small voltage offset from VCC (or from GND) on the offending signal, an offset small enough to be quite easily overlooked.
The datasheet specifies 32 mA output at 4.5 V supply, but that's rated output current. Peak current into a dead short is rather around 150 mA (not that the chip would be expected to survive it very long either).
dirt cheap, preferable 2-3 or more parts in a package
ive them all from a single IC, 3 pcs is too expensive.
ance of about 17 ohms, but about 3 times to high
The problem is not driving them on, but making sure that when they are off, that they stay off. Say you have a half bridge configuration and the top F ET has been on. It is turned off, and some ns later, the lowside FET is tur ned on. WHen the midpoint voltage ramps quickly to GND, then the source-gat e capacitance of the high side FET is subjected to high dV/dt, and that cur rent runs out of the gate driver for the highside FET. So if the high side FET driver has non-zere impedance, the gate voltage will rise during the mi dpoint travelling to GND and that is enough to turn on the high side FET wh ich translates into cross conduction. BAD
I don't have that luxury :-)
ed, but then the manufacturer knows well that he can ask for a higher price :-(
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