How to select a logic level MOSFET at Mouser?? - Page 1
Forum section: electronics / projects

author: luiHS
author_rank: Frequent Contributor
timestamp: October 07, 2022, 07:32:38 pm
content: Hi.I need to connect power MOSFETs to a RT1064 microcontroller to activate coils at 50v, if possible I would like MOSFETs that can be connected directly to the GPIOs of a microcontroller at 3.3v, so that they can supply all the current without the need to add another transistor between the GPIO and the MOSFET.What I don't know is what parameter to filter in Mouser's component selector, to select MOSFETs of this type (Logic level MOSFET). I have seen some graphs that relate Gate Source Voltage to Drain Current, but I have to open the datasheets to see it.

author: Faranight
author_rank: Unknown
timestamp: October 07, 2022, 07:58:28 pm
content: I often have similar problems with filters. Sometimes there just isn't an option for what you want. In case of logic level mosfets I sometimes use the gate-source threshold voltage and set it really low to filter out non-logic level fets. Be sure to check the datasheet of the component before buying it.I also learned that you can use pretty much any website (digikey, mouser, farnell, tme, rs, etc) to search for components you want. Pick the website that has the best filtering options. You can even go to some manufacturers websites and use their online product selection catalog. Find the part that you need then go back to Mouser and buy it there.

author: nctnico
author_rank: Super Contributor
timestamp: October 07, 2022, 09:46:22 pm
content: Unfortunately it takes opening lots of datasheets to learn the details of a Mosfet. Vgs can be specified at different currents and made to look better than it is in reality.However, when it comes to driving relays and so on, I prefer to use a dedicated driver chip that has current limiting, overvoltage protection and (if possible) temperature protection. Something like their TPIC6A595 from TI but with it's 50V spec, it could be at the limit of your application. Maybe there are devices that allow switching a higher voltage.

author: JPortici
author_rank: Super Contributor
timestamp: October 08, 2022, 06:08:04 am
content: As other suggested, filtering for VTH is the first thing to do.But be sure to confirm with the datasheet, because the monkey filling the mouser database could have put a wrong value, or the minimum guaranteed vth instead of the typical/maxOr the datasheet could note an adequate value for max VTH but then you go to the VSG/ID chart and see you need a couple more volts to achieve the required RDSON/IDIt's been a while since i looked but at the time i could find adequate 3.3V mosfets only up to 30-40V Vds, maybe a few for 50, practically none for > 100V, i needed about 150Volts. I had to either use drivers, or 5V logic translation between the MCU and the gates.

author: Jeroen3
author_rank: Super Contributor
timestamp: October 08, 2022, 08:12:39 am
content: Quote from: luiHS on October 07, 2022, 07:32:38 pmDepends on the size of the mosfet. Big ones and high voltage are probably not suitable for direct gpio. Smaller ones with lower voltage will probably work.A catalog Vgsth of 1-2-ish volts will put in the right search area. Vgsth increases with Vds.Make sure you don't pick one with enormous gate capacitance, like 50A mosfets, your mcu pin will hate you for it and it will switch slow.If you're going to use PWM, get a gate driver.For example:PMT280ENEAWill be around 400 mOhm at 3V gate for 1A.Then of course there are smart mosfet with schmitt trigger inputs and flyback clamping if you pick the high side ones nctnico talks about. But we're still not recovered from the big shortage, so good luck on those.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 08, 2022, 09:19:28 am
content: Work out a range of specs.First search the major (and minor) manafacturers sites.IR, Rohm, Fairchild, Infinon, Ixys etc, etc.Use thier selection tables , then find out if you can buy it.The catalog sites have rubbish sorting tools by and large.

author: luiHS
author_rank: Frequent Contributor
timestamp: October 10, 2022, 03:33:01 am
content: Can this MOSFET be considered as Logic Level ?https://www.mouser.es/ProductDetail/onsemi-Fairchild/FDD86102LZ?qs=dIxESgyDOriq9LDJtrMcmg%3D%3DI look at the graph that relates the gate voltage to the drain current. It seems that with 3v from the gate it could supply up to 30 Amps, with a maximum voltage of 100v.I made a selection of MOSFETs whose Vgs th is less than 1v, that can supply at least 30 Amps, work at a voltage not less than 70v and that are SMD. Only 13 remained after applying those filters at Mouser.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 10, 2022, 04:31:44 am
content: Well, this one may work, but not the best fit IMO.- VGSth is anywhere between 1V and 3V (the max is a bit high for my taste for a 3.3V logic output.)What you'd risk here is to have significant power loss if you're not lucky with a specific part, and depending on temperature.I would prefer this part for instance for your case: IPD30N06S4L-23. It's available.Be aware that those power MOSFETs have a significant input capacitance. Your GPIO shouldn't have any problem driving it, but do not expect any fast switching. If the switching time is not very important for your application (and thus switching frequency is low), this won't be a problem. If you need fast switching time though, you'll need a gate driver. There's no way around it - you won't find power MOSFETs with much lower input capacitance.

author: luiHS
author_rank: Frequent Contributor
timestamp: October 10, 2022, 04:46:16 am
content: Quote from: SiliconWizard on October 10, 2022, 04:31:44 amCould I use a buffer like the 74HCT245 or does it have to be a transistor?

author: exmadscientist
author_rank: Frequent Contributor
timestamp: October 10, 2022, 07:03:28 am
content: Quote from: luiHS on October 10, 2022, 04:46:16 am'HCT245 can work but HC(T) logic doesn't have much more drive (6mA) than your typical microcontroller (sometimes less). LVT or ABT family devices are a bit better at 32mA sourcing, but that may not be enough for an external MOSFET. Or it might. It depends! Often it's not good enough and transistors or a gate driver class buffer are required.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 10, 2022, 06:00:09 pm
content: Quote from: exmadscientist on October 10, 2022, 07:03:28 amYep. Note that a single-transistor arrangement for a gate driver has limitations: it will be able to either source or sink current to the gate, but not both. So there will typically be a pull-up (or pull-down) resistor, which will make one of the edges dead slow. If you're going to make your own decent gate driver, you'll need at least two transistors, unless one of the edges doesn't matter in your application (for instance, if you need fast switch-on time but don't care about the switch-off time). At which point, it may be easier (if not more cost-effective) to use an integrated gate driver.

author: luiHS
author_rank: Frequent Contributor
timestamp: October 10, 2022, 06:52:03 pm
content: Quote from: SiliconWizard on October 10, 2022, 06:00:09 pmBesides the circuit with two NPN transistors (or 2 MOSFETs) and the power MOSFET, what other circuit can be used to get the best results?.What is an integrated gate driver, can you provide an example schematic?.I have seen some scheme, like the attached one, in which a 74xx chip is used as a buffer between the processor and the power MOSFET.

author: Haldor
author_rank: Newbie
timestamp: October 10, 2022, 06:52:49 pm
content: If you don't want to design a FET circuit, then just select a high-side or low-side switch. Low side switches are cheaper than high side switches so that is what I normally use unless the application requires a high-side switch.Here is an example of my query to find an appropriate low-side switch.https://www.mouser.com/c/semiconductors/power-management-ics/power-switch-ics-power-distribution/?q=low%20side%20switch&operating%20supply%20voltage=8%20V%20to%2050%20V~~8%20V%20to%2065%20V%7C~60%20V&type=Low%20Side~~Low-Side&rp=semiconductors%2Fpower-management-ics%2Fpower-switch-ics-power-distribution%7C~Type%7C~Operating%20Supply%20VoltageNote: Also be sure to bypass the coil with a flyback suppression diode to prevent back EMF from causing noise or even damage when you turn the coil off.https://en.wikipedia.org/wiki/Flyback_diode

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 10, 2022, 07:08:36 pm
content: Quote from: luiHS on October 10, 2022, 06:52:03 pmThose are just ICs which provide gate driving functionality in a single chip with guaranteed specs. You can look for "MOSFET gate driver".But otherwise, there are also fully integrated power switches than can be controlled from a GPIO directly, like Haldor suggested. Those embed both the gate driving circuitry and the power MOSFET in a single chip. Now while they are very easy to use, they may not be very cost-effective compared to a more discrete approach. Look at the prices (and make sure they can pass enough current and can operate at at least 50V) to see if that'd be a match for your application.

author: luiHS
author_rank: Frequent Contributor
timestamp: October 10, 2022, 08:11:03 pm
content: Quote from: SiliconWizard on October 10, 2022, 07:08:36 pmYes, I have seen them, but they are somewhat expensive, I prefer the conventional solution with transistors and power MOSFETs. Or a power MOSFET with gate logic level and a 74xx as buffer between GPIO and MOSFET.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 11, 2022, 05:04:04 pm
content: I've yet to come upon a functioning alphanumeric sorter on any web page. Ever!When will "exclude" be added. Cheapskate web designers.... Don't get me started.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 11, 2022, 06:20:37 pm
content: Quote from: luiHS on October 10, 2022, 08:11:03 pmI don't think you have told us what you are doing with those coils and if you really need fast switching. If not, as I said, driving the MOSFET directly from a GPIO may even be an option.