High side, high voltage (~60V) N-FET driver chips

Really? I couldn't find that info in the app notes but maybe I overlooked it.

robert

You mean irf5210, right? $4.23 each at DigiKey. Nice.

WRT John's circuit, I like to use a current-source drive, which doesn't depend on the exact value of the high-side supply to set the MOSFET's gate voltage, R1 = 2.5 * R2, etc., for 5V logic drive. And a bipolar on the bottom is faster and easier, due to its much lower capacitances. An mpsa42 or a 2n5551, etc., will work well.

A bipolar across R1, plus three more resistors, lets one add a foldback current limit to protect the PCH in the event of an output short -- but that's not needed if the +55V source is current limited.

I hope you intend to put a few hundred pF across R2. Ewww, exponential gate voltage drive!

Tim

-- Deep Fryer: A very philosophical monk. Website @

This is right out of the pin description section on the 4080A datasheet:

B High-side Bootstrap supply. External bootstrap diode and capacitor are required. Connect cathode of bootstrap diode and positive side of bootstrap capacitor to this pin. Internal charge pump supplies 30 A out of this pin to maintain bootstrap supply. Internal circuitry clamps the bootstrap supply to approximately 12.8V.

This above circuit is really the simplest way to go. P-channel FETs are not as abundant as N-channel, but there are still many to choose from. You can parallel to get better Rds_on. I think I already mentioned that gate driver ICs are really meant to be used in high speed switching power supply topologies. It gets complicated to use them in apps where the swtich needs to be on indefinitely.

P-Channel, bi-polar, and a couple resistors - what could be simpler?

Only problem there is that a short puts the MOSFET into the linear region, and if you designed it only with switching in mind, that could destroy it rapidly. Is there a simple way to modify this protection to turn on hard on a sustained high current, or do you have to resort to triggering a shut- down elsewhere?

Clifford Heath.

As I said, a BJT plus three resistors to add an honest foldback current limit, and I should also have stated, IS STRONGLY RECOMMENDED, unless the power source is current limited. Hopefully I don't have to make another ASCII drawing. There are lots of drawings out there: in our book AoE, in posts I've made on s.e.d., and on the web.

Yes, sorry Win, I just checked AoE. I didn't realize that foldback was so easy, and thought you meant a simple current limit.

Very well my son, go and sin no more. ;-)

Doesn't he have to buy five copies of the third edition, too? ;-)