Need help IDing MOSFET - Page 1
Forum section: electronics / beginners

author: TT_Vert
author_rank: Regular Contributor
timestamp: February 21, 2018, 06:36:21 am
content: I have attached the image. I did quite a bit of research on the marking (A0LA) and have figured out it is made by HP and is a HSMS-2800. At least that is how I interpreted what I've read. I cannot find anything else about this, no datasheet or anything. So my question is, am I on the right track? IF A0 is in face designating it as a HSMS-2800 what does the LA and the SX mean? I read those may be dates but I don't know. If they are dates, do I just need to get any MOSFET starting w/ A0?In fact, maybe it's not a MOSFET and this may be what I'm looking for?http://www.g3ynh.info/circuits/diode_data/Avago_HSMS-280ser.pdfThanks and I apologize for the very basic question.Thanks much,Dave

author: newbrain
author_rank: Super Contributor
timestamp: February 21, 2018, 12:44:44 pm
content: The code has 4 characters, and looks like SOT-23, it could possibly bethis one(fromhttp://www.s-manuals.com/smd).Try to understand whether it's a double diode or a MOSFET from its surroundings...

author: TT_Vert
author_rank: Regular Contributor
timestamp: February 21, 2018, 06:12:07 pm
content: It's definately a SOT23. I saw that one you linked yesterday. What makes you think it's no the 2800 vs the 3400 you linked? I did see that yesterday when researching as well. I did try to trace the circuit last night to understand how it was working but I'm pretty green. What I found was (Assuming the top leg is the drain and the bottom left source, right gate is the following.Top leg (drain?) Goes directly to the negative side of what should be a PWM fan (Constant 24+ on other side so this makes sense)Bottom left leg goes to a 10k ohm resistor which then goes to groundBottom right leg goes to an unmarked SMD cap, then a 470 and 100K ohm resistor then to pin 2 of a 4988ET. Pin 2 of this seems to be the enable pin. I think there is more on this leg (I'm fairing sure this side goes to a pin 9 on this same chip (MS1 logic input) perhaps telling the chip that the PWM pin 2 is enabled but I don't have a schematic and there are few visible traces. I suppose I could continue to try to probe w/ my meter but I figured I had enough info. Maybe this will help someone help me. Given the A0LA does this help anyone? It seems w/ these markings it is still very difficult to ID this component.I took a bit and tried to trace it and draw it the best I could. I also included a pic of this part of the circuit on the PCB. Disregard the bodge wire, just doing some testing. Sorry for the horrible drawing but it's the best I could do as a newb. The caps are unmarked but i put a C for them. I should have done the -| |- but I figured I'd just confuse myself when trying to draw it out..Dave

author: newbrain
author_rank: Super Contributor
timestamp: February 21, 2018, 09:06:59 pm
content: Quote from: TT_Vert on February 21, 2018, 06:12:07 pmThe 4 character code, plus the 90 degree rotated assembly lot code, see page 7 of the 3400 datasheet.The 2800 seems to have just 3 characters, page 2 of the DS you posted.

author: TT_Vert
author_rank: Regular Contributor
timestamp: February 21, 2018, 11:14:32 pm
content: Ahh i see what you're saying about the PN. Wow what a pain this is. I assume the more you do it the easier it gets but most of the components I looked up I figured out right away. Given that many SOT23 components look the same do people just know the numbering schemes over time and know if something is a MOSFET , diode, etc? How would one ID these caps given they have no marking? Hope for a schematic or test each one?Also going back to where you stated the following "Try to understand whether it's a double diode or a MOSFET from its surroundings.." does this still matter if it's a 3400? I don't see any difference 3400s in the datasheet like the 2800 had. With that said I did confirm on a good board that source is always grounded and that the drain goes to the fan ground. I guess anyone who knows more about the design knew that before I mentioned much of anything. I'm very curious to figure out how this main processor chip controls this MOSFET via PWM. I assume something with the resistors excites the drain and allows current to flow from the source to the drain in a controlled PWM manner but that is where I get confused. Especially given I don't have a schematic to mull over aside from what I tried to cobble together.Thanks again you've been very helpful for this newb.Dave

author: TT_Vert
author_rank: Regular Contributor
timestamp: February 22, 2018, 09:31:55 pm
content: I have one last question. As it turns out the AO3400 is not available at digikey. I spoke with them about an alternative PN and they gave me DMN3404LDITR-ND which is similar but has a few differences which I'm hoping you guys can help me understand the repercussions of changing.A03400 vs. DMN3404LDrive voltage2.5V, 10V vs. 3V, 10VVgs (th) MAX(I understand this the voltages at which the mosfet will allow current flow but how does this work when it's a ground? Is a positive voltage always applied to the gate to allow current from source to drain? This spec has me a bit concerned (See below)1.5V @ 250µA vs 2V @ 250µAGate charge(I have little understand of this aside from it's the speed at which is switches? But I'm confused with the voltage as they're signifigantly different.)7nC @ 4.5V vs. 9.2nC @ 10VVgs (Max)(I understand this to be max voltage between Gate and source but if it's a ground as a source does this matter?+/-12V, +/-20VInput Capacitance630pF @ 15V vs. 386pF @ 15VPower dissipation(Not sure if this is an issue but it's half the dissipation of what was in place)1.4W (Ta) vs 720mW (Ta)Rds On (Max) @ Id, Vgs(This doesn't seem very significant26.5 mOhm @ 5.7A, 10V vs 28 mOhm @ 5.8A, 10VThanks again and I'll continue to research but maybe you guys could put it in layman's terms for me in the meantime.Vgs(th) concernResearching a bit more about threshold voltage I have a concern. The mosfet recommended by digikey (DMN3404L) as a replacement for the AO3200 is different to the point I don't know if it'll work. What is one to do when they don't have any specs to determine what voltage is being sent to the gate? This is what I'm seeing for specs:Vgs (th) MAX AO3200 vs. DMN3404L min, typical, max0.65, 1.05, 1.45 vs. 1.0, 1.5, 2.0.As you can see the typical Vgs (th) of the recommended mosfet is actually ABOVE the MAX for the mosfet that was in thereDave.