[CLOSED] Looking for very low guaranteed Idss<=100nA P-channel Mosfet - Page 1
Forum section: electronics / projects

author: eleguy
author_rank: Regular Contributor
timestamp: November 30, 2023, 04:42:27 pm
content: Has someone seen or maybe even used any very low Idss Mosfets? With "very low" I mean 100nA (guaranteed) but preferable even less. So far I have only found FemtoFETs (like CSD23381F4) from Texas but it seems not to be (at least) JLCPCB "friendly" meaning they would ask $$ extra for assembling those on the board.Additional reguirementsId >= 10mATa = "ambient"Part is in active production stateEDIT, Case is closedThanks all for the effort in trying to help or push me to the correct (or at least most reasonable) direction.

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 30, 2023, 04:57:36 pm
content: At that level you'll probably have to test yourself, and also that 100nA spec is at 25C

author: eleguy
author_rank: Regular Contributor
timestamp: November 30, 2023, 05:00:31 pm
content: Quote from: PartialDischarge on November 30, 2023, 04:57:36 pmyep, I just thought if there would be a way to avoid that "hassle".

author: Marco
author_rank: Super Contributor
timestamp: November 30, 2023, 05:41:30 pm
content: Have you searched for low leakage load switches? For generic MOSFETs it's going to be a tough datapoint to search for, but for load switches it's a much more up front design parameter.

author: eleguy
author_rank: Regular Contributor
timestamp: November 30, 2023, 05:53:57 pm
content: Quote from: Marco on November 30, 2023, 05:41:30 pmYes. Something like MAX14662 does the job in the switch on/off only application. I just wonder if one could manage also something between with limited BOM. Certainly I can punch in both (switch and the mosfet) but if there is a low Idss mosfet somewhere that would be the best fit this time.

author: Zero999
author_rank: Super Contributor
timestamp: November 30, 2023, 08:58:12 pm
content: What's the maximum drain current?Smaller, lower power rated devices will have a lower leakage current. A higher threshold, lower gate change, higher RON, and current rating, are conducive to less leakage. I don't know about voltage rating. Higher voltage rated parts, are normally physically much larger, everything else being equal, but running at a much lower voltage will reduce the off current considerably.What's the maximum temperature? The higher the temperature, the higher the off current.I think many manufactures don't actually test the off current. They appear to slap the same rating on all of their data sheets. Testing at a higher temperature and voltage, than you'll ever run the device at will ensure all devices will meet your desired specifications.

author: David Hess
author_rank: Super Contributor
timestamp: December 01, 2023, 12:49:08 am
content: Would old school small signal MOSFETs be suitable? The 3N163/3N164 from Linear Systems is 400/800 picoamps maximum:https://www.linearsystems.com/mosfets/3n163-seriesCalogic has small signal low leakage p-channel MOSFETs also:http://calogic.net/products/mosfets/

author: eleguy
author_rank: Regular Contributor
timestamp: December 01, 2023, 06:10:24 am
content: Quote from: Zero999 on November 30, 2023, 08:58:12 pmAnything >=10mA will be enoughQuote from: Zero999 on November 30, 2023, 08:58:12 pm"Room" temperatureQuote from: Zero999 on November 30, 2023, 08:58:12 pmThat is what I have now started to think as well. Lazy guys.Quote from: Zero999 on November 30, 2023, 08:58:12 pmThanks for reminding the good testing thumb-rules! It starts to look like one just cannot avoid that...

author: eleguy
author_rank: Regular Contributor
timestamp: December 01, 2023, 06:21:38 am
content: Quote from: David Hess on December 01, 2023, 12:49:08 amInteresting parts. Thanks for the hint but both of these are maybe too old school as at least Mouser and Digikey think they are obsolete and non-stocked anymore.Quote from: David Hess on December 01, 2023, 12:49:08 amOh no! These goodies (at least the P-channel ones) are also obsolete.

author: ArdWar
author_rank: Frequent Contributor
timestamp: December 01, 2023, 07:24:51 am
content: Quote from: eleguy on December 01, 2023, 06:21:38 amIt isstill available.It should be fine for one time buy, although if you project extended product volume/lifetime it might be unwise to depend on what's basically single supply boutique manufacturer.

author: eleguy
author_rank: Regular Contributor
timestamp: December 01, 2023, 07:47:23 am
content: Quote from: ArdWar on December 01, 2023, 07:24:51 amOk, my bad. My search screens got apparently bit messed. Thanks for clarification. But but... availability is a bit suspicious factor in a longer term. I would then rather select one of those FemtoFETs from the TI. Those are recently pushed into the production and are even somewhat cheaper. But before committing into their footprints I might have to just test out manually some other parts we use anyhow. Maybe their specs are good enough in reality.

author: voltsandjolts
author_rank: Unknown
timestamp: December 01, 2023, 08:55:25 am
content: Not a P-FET but SSR for example:VOR1142M4

author: magic
author_rank: Super Contributor
timestamp: December 01, 2023, 08:57:55 am
content: Don't be silly, make it SOT23 or SOT323 and find suitable parts, it shouldn't take long.1μA means "fuck off, we aren't testing this for you". I pulled out a few 2N7000, applied 12V to the drain and connected gate and source shorted together to a DMM in 10MΩ impedance volts range (black probe grounded). The DMM was reading 0.1V for one unity and a few mV for another two. And 12V for yet another, apparently I blew its gate oxide - later found 400kΩ between gate and drain.0.1V/10MΩ is 10nA and this was the worst one that wasn't obviously blown. The other two were sub-1nA.Yes, it's THT and N-ch, but you get the point hopefullyeditMake sure that JLCPCB won't grab some random Shenzen market special for you if you specify a generic enough part number...

author: Zero999
author_rank: Super Contributor
timestamp: December 01, 2023, 08:59:24 am
content: Quote from: eleguy on December 01, 2023, 06:10:24 amSorry, I meant voltage. What's the maximum voltage? And what voltage drop, whist it's on, is acceptable?Why not use a BJT?

author: eleguy
author_rank: Regular Contributor
timestamp: December 01, 2023, 09:41:11 am
content: Quote from: magic on December 01, 2023, 08:57:55 amThanks!!! No no.. silly I try not to be but cannot guarantee that even at the room temperature. Here I am already testing. So it seems to be (as we kind of knew already) that most of the mosfets I have tested so far do fulfill my "low" specs. Even the JLCPCB friendly basic part SI2301CDS seems to do the job. At least all of 5 I have tested so far.Ok, so this is what you get when trying to avoid manual testing. Haha... I call this case closed. It feels like I can somewhat easily find a p-mos that fits to the job. Let the final board tester - uups it is also me - then find those "faulty" units if such even ever appear.Thanks all for the effort in trying to help or push me to the correct (or at least most reasonable) direction.

author: magic
author_rank: Super Contributor
timestamp: December 01, 2023, 09:52:57 am
content: Probably the best types will be ones with small junction. This means low current, high RDS(on), low capacitance.I have some NXP BSS84AK (180mA, 4.5Ω) which look promising, but it would take me much more effort to test SMD parts and to test them to their full potential so I'm afraid I won't. Actually, the few mV that I observed with good 2N7000 samples fluctuated a fair bit and it may have been noise, with actual leakage being 1pA or less.

author: ArdWar
author_rank: Frequent Contributor
timestamp: December 01, 2023, 10:40:53 am
content: Now I'm curious how a random MOSFET fares on Idss.Here's from IRFP150 that I know for sure is a fake. Sorry, not everyone just happen to have PMOS on handRoom tempWith soldering iron stuck to the mounting holeNot bad actually. It being fake might actually helps here, being smaller die and all

author: David Hess
author_rank: Super Contributor
timestamp: December 01, 2023, 11:53:50 am
content: Quote from: ArdWar on December 01, 2023, 07:24:51 amYou have to buy them through their distributors which do not include Mouser or Digikey unfortunately. These are the kinds of parts often found in leading edge test instruments which have to work at the lowest currents. I consider both companies reliable, but you might have to wait for availability.

author: Whales
author_rank: Super Contributor
timestamp: December 01, 2023, 12:03:47 pm
content: Is the impedance of an off-state mosfet ohmic? Can you (assuming you're going for a common-source configuration) use several mosfets in series with their gates tied together?