How to use a high side gate driver IC - Page 1
Forum section: electronics / projects

author: T_guttata
author_rank: Regular Contributor
timestamp: September 07, 2021, 06:00:10 pm
content: Hi everyoneCould anyone explain me how I could use an N-channel MOSFET as a high side switch with the help of a gate driver IC such as the infineon IRS2572https://www.infineon.com/dgdl/Infineon-IRS25752L-DS-v01_02-EN.pdf?fileId=5546d462533600a40153567b388b2839?I would like to permanently turn on and off the high side N-channel MOSFET with a 5V signal.The schematic indicated in the data sheet will not work, right?What are typical applications of this IC?Thanks for your help!

author: m98
author_rank: Frequent Contributor
timestamp: September 07, 2021, 06:15:32 pm
content: The schematic indicated in the data sheet does work, and the typical applications of a high-side gate driver is to drive high-side gates.edit: Oops, missed the crucial part of the questionThere are drivers that allow static drive by having an integrated charge-pump:https://www.analog.com/en/products/ltc7004.html#product-overview

author: Ian.M
author_rank: Super Contributor
timestamp: September 07, 2021, 06:29:00 pm
content: A typical high side gate driver like the one you linked requires PWM drive with a maximum duty cycle limit, as it requires time with the MOSFET off and its source at a very near ground potential for the boost capacitor to charge up via the bootstrap diode, to provide a gate drive voltage that rises above the positive supply when the MOSFET is on. If you need it to stay on all the time, you need a driver with an internal charge pump driven by an internal oscillator, or you need to bodge on an external high isolation, low isolation capacitance DC-DC converter in place of the bootstrap diode to feed the boost capacitor with a supply that can swing with the MOSFET source. Note, that the DC-DC converter requires an isolated secondary and rectifier per MOSFET driver - two cant share.TLDR: the chip you chose wont do what you want it to!

author: Benta
author_rank: Super Contributor
timestamp: September 07, 2021, 06:45:53 pm
content: As Ian.M says, typical high-side MOSFET drivers need constant switching to keep the bootstrap supply active.If you only need static drive and low speed switching, a nice solution is photovoltaic optocouplers. This is one of the best:https://www.vishay.com/docs/84639/vo1263aa.pdfNow, ~40 uA is not a lot, but you can double it by using two (or more) in parallel. You'll need a gate pull-down resistor as well for guaranteed turn off.Nanosecond switching times you'll never achieve, but below 1 ms is realistic.

author: T_guttata
author_rank: Regular Contributor
timestamp: September 07, 2021, 07:11:55 pm
content: I had to learn it the hard way that the circuit does not work, if the input signal is just 5V but no PWM (fortunately PCBs are cheap these days and the lost money is no big deal) . So therefore, there is no easy way to use N-channel mosfets for high side applications without PWM.The reason I wanted to do that is because N-channel mosfets have lower RDS_on, but in that case I will search for a P-channel MOSFET with low enough RDS_on. They are rare, but they exist.

author: langwadt
author_rank: Super Contributor
timestamp: September 07, 2021, 07:28:44 pm
content: Quote from: T_guttata on September 07, 2021, 07:11:55 pmwhat voltage? there are lots of high side switches, easy to drive and usually protected against most kinds of abuse

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 07, 2021, 07:31:06 pm
content: The bootstrap driver is okay if it has power. You can use an isolated DC-DC converter or charge pump supply for this. Note that the charge pump must be rated for the full voltage swing, so it's not that easy to pull off at high voltages.Tim

author: T_guttata
author_rank: Regular Contributor
timestamp: September 07, 2021, 07:37:59 pm
content: 30V high side. Just switch on/off is everything I need, no PWM or high frequency stuff.

author: langwadt
author_rank: Super Contributor
timestamp: September 07, 2021, 07:52:56 pm
content: Quote from: T_guttata on September 07, 2021, 07:37:59 pmmax current?

author: T_guttata
author_rank: Regular Contributor
timestamp: September 07, 2021, 08:06:35 pm
content: Very high, but not continous. Therefore I don't expect thermal issues.But I mean max current will be determined by RDSon of the MOSFET? I don't see how it's related to the gate driver circuitry?

author: MadScientist
author_rank: Frequent Contributor
timestamp: September 07, 2021, 08:08:28 pm
content: Ltc7001 N channel gate driver with integrated charge pump , 100% on time

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 07, 2021, 08:16:46 pm
content: Well, two things:Lower Rds(on) simply has higher Qg. Higher current means more power during transition. You need switching at least fast enough not to destroy the device during switching. This might completely rule out PV type drivers, for example.If you use PMOS, performance is a good ~2.5x worse than NMOS, and this contributes both in terms of physical size (you might not even be able to get a low enough Rds(on) in the package size you were hoping for) and gate charge (more Qg). It's also more expensive, of course.If you're only running for a few ms at a time, that's probably not a big deal as far as thermals; switching does need to be fast enough not to blow up, but as long as you have a modest safety margin on that, the added power due to conduction will be small.If the duration is some seconds, you get no advantage from thermal inertia, and need it basically well enough heatsunk for continuous operation. Thermal mass is the only thing you can skimp on, with semiconductors; you need at least enough electrical capacity to begin with, and then enough dissipation to make use of it at whatever duty cycle, pulse length or other basis you're using it at.Also, mind that, if the load has a capacitive characteristic, you need to supply that energy during turn-on, in addition to whatever switching (turn-on) losses the load current requires.Conversely, if inductive, you need to dissipate that energy during turn-off. Here at least, you can add a catch diode so the load dissipates its own energy. Assuming it doesn't need fast turn-off (for something like a solenoid, the time required for decay of magnetic energy, adds with that required for mechanical motion). If it does need fast turn-off, a TVS diode can provide that dump without damaging the transistor (the transistor then needs to be rated for maximum Vin plus diode Vp).Tim

author: langwadt
author_rank: Super Contributor
timestamp: September 07, 2021, 08:41:48 pm
content: Quote from: T_guttata on September 07, 2021, 08:06:35 pmdepending on how much current you need you can get it all in a single part, no need for a seperate fet and driver

author: T_guttata
author_rank: Regular Contributor
timestamp: September 07, 2021, 08:45:56 pm
content: Thanks for the detailed explanations. The mentioned gate driver IC with integrated charge pump is very expensive. N channel mosfet + this driver ic will be significantly more expensive than a P-channel mosfet.