"document and peer review"... Exactly. I believe, for exactly the same reasons, that this is completely = fine, but I cannot in good conscience rely on that in this application.=20 For most of the other products I've designed over the years, I'd be 100% co= nfident that it would work whether we built 1 or 10,000,000. (Been both pla= ces, done both) I take these designs VERY seriously.=20 The data sheet simply gives no hard information on the unloaded case.=20 -- David VanHorn Lead Hardware Engineer Backcountry Access, Inc. 2820 Wilderness Pl, Unit H Boulder, CO =A080301 USA phone:=A0303-417-1345 =A0x110 email:=A0david.vanhorn@backcountryaccess.com=A0 -----Original Message----- From: piclist-bounces@mit.edu On Behalf Of Stephe= n Forrest Sent: Wednesday, June 5, 2019 7:29 PM To: Microcontroller discussion list - Public. Subject: Re: RE: [EE] Hi David - I understand your abundance of caution. Here's my take: If I understand, you are loading a PIC output with logic gate that has an i= nput leakage current of 1 uA (microamp to be sure). Vdd for the system is 3= V3. The datasheet in table 32.9 param. DO20 gives 4 data points for Vout. The one you referenced was for Vcc =3D 3V6 and Iout =3D 3mA (milliamp to be= sure). Plot Vdd-Vout for ALL four points and then consider 0 amps load (no= D/S value so be as liberal as you like for worst case...). Fit curves to e= ach set then plot YOUR conditions. PIC's are CMOS devices. The output structures are CMOS FETs (with protectio= n diodes) (an FAE can verify if in question), so Vds *will* reduce as Ids r= educes. Not linear but almost certainly monotonically. Vout for the PIC I/O= is then Vdd-Vds (with some variation for leakage current). I'm sure you wi= ll be able to draw valid conclusions. I have made some assumptions, so not all datasheet backed (datasheets are s= ubject to change anyway) but I have applied my professional training, exper= ience and judgment in those assumptions. My take is you'll be fine but "doc= ument and peer review"... Stephen On Thu, Jun 6, 2019 at 7:24 AM David Van Horn < david.vanhorn@backcountryac= cess.com> wrote: > " If it's life critical, doing anything the manufacturer doesn't=20 > recommend would tend to be viewed as negligent" > > Exactly. The corner case I'm trying to resolve is not covered by the=20 > data sheet. > Microchip knows who we are and what we do. We've been using them for=20 > a LONG time. > > " and you want to be rather creative with certainty. " I take offence > at this statement. I am looking for documentation that will either > establish that what I'm attempting is in spec, or is not in spec. If=20 > not, then I can justify the cost of the additional glue. If it's in spec= , then > I will have the documentation to back it up. How do you see this as > "rather creative"? > > > > -- > David VanHorn > Lead Hardware Engineer > > Backcountry Access, Inc. > 2820 Wilderness Pl, Unit H > Boulder, CO 80301 USA > phone: 303-417-1345 x110 > email: david.vanhorn@backcountryaccess.com > > -----Original Message----- > From: piclist-bounces@mit.edu On Behalf Of=20 > mad.scientist.at.large@tutanota.com > Sent: Wednesday, June 5, 2019 2:55 PM > To: Microcontroller discussion list - Public. > Subject: Re: RE: [EE] > > If it's life critical, doing anything the manufacturer doesn't=20 > recommend would tend to be viewed as negligent. No one will sell you sem= i's for > "life critical" applications without knowing what you are doing. By you= r > own statements they shouldn't sell to you, and you want to be rather > creative with certainty. Even if you did 100% screening you still would > have no idea how they aged when operating off spec. Perfectly fine=20 > for toys, or even most consumer goods by some standards. Only the=20 > manufacturer may know enough about the fine details to have some idea=20 > how workable this is in a critical application. > > "Would you like to see us rule again, my friend? All you have to do is > follow the worms." Pink Floyd, The Wall, Waiting for the worms > > > > > Jun 5, 2019, 2:38 PM by david.vanhorn@backcountryaccess.com: > > > No game.. > > > > Check the web site. Our products are not toys. If they don't work, > people die. Absolutely zero exaggeration there. ZERO tolerance for=20 > hobby hacks. > > > > That said, I need to find economical solutions. If I don't need=20 > > extra > parts to make this work then I'm very happy. If I know I can't get=20 > there and be 100% inside data sheet specs with all component=20 > tolerances accounted for then that justifies whatever extra glue is neede= d. But I need to know > one way or the other. At the moment, I'm leaning toward the glue simp= ly > because I can't find enough supporting docs to say "this works and I=20 > can bet my life on it.". > > I have to guarantee functionality under all spec'd operational > conditions. > > > > If I won't bet my life on this product, why should you? > > > > Never read the book, but I've been tempted several times. > > > > I'm just hoping someone knows of an app note or similar that I can > reference one way or the other. > > > > > > -- > > David VanHorn > > Lead Hardware Engineer > > > > Backcountry Access, Inc. > > 2820 Wilderness Pl, Unit H > > Boulder, CO 80301 USA > > phone: 303-417-1345 x110 > > email: david.vanhorn@backcountryaccess.com > > > > -----Original Message----- > > From: piclist-bounces@mit.edu On Behalf Of=20 > > Kerry > > Sent: Wednesday, June 5, 2019 2:25 PM > > To: piclist@mit.edu > > Subject: Re: [EE] > > > > I think, therefor I am. All else is speculation and supposition. > > > > It is starting to sound like 1 of 3 things: > > 1) You are playing some sort of a game with us. > > 2) You are on the verge of a nervous breakdown. > > 3) You are 2/3 of the way through reading "Zen and the Art of > Motorcycle Maintenance" > > > > > > > > On 6/5/2019 12:59 PM, David Van Horn wrote: > > > >> Agreed, but that assumes that the output fets are really linear > resistors at this operating point. > >> I believe that is true, but I don't know it to be true. > >> > >> > >> -- > >> David VanHorn > >> Lead Hardware Engineer > >> > >> Backcountry Access, Inc. > >> 2820 Wilderness Pl, Unit H > >> Boulder, CO 80301 USA > >> phone: 303-417-1345 x110 > >> email: david.vanhorn@backcountryaccess.com > >> > >> -----Original Message----- > >> From: piclist-bounces@mit.edu On Behalf=20 > >> Of Kerry > >> Sent: Wednesday, June 5, 2019 8:14 AM > >> To: piclist@mit.edu > >> Subject: Re: [EE] > >> > >> Take the scientific approach. > >> > >> The ON resistance of the output FET is (VCC - VOUT) / IOUT. The=20 > >> data sheet uses 3.6V as VCC, and specifies a 3mA load. Say the=20 > >> output voltage is specified as 3.3V. The FET on resistance would=20 > >> be .3V/.003A =3D 100 Ohms. At VCC =3D 3.3V and 1 uA load, output=20 > >> voltage would be 3.3V - > >> (.000001 A * 100 Ohms) =3D 3.299V > >> > >> Kerry > >> > >> > >> On 6/5/2019 7:47 AM, David Van Horn wrote: > >> > >>> Agreed on both counts, but I'm reluctant to move forward without > something in writing. > >>> I could measure hundreds of chips, but that says little about the=20 > >>> next > batch. > >>> > >>> -- > >>> David VanHorn > >>> Lead Hardware Engineer > >>> > >>> Backcountry Access, Inc. > >>> 2820 Wilderness Pl, Unit H > >>> Boulder, CO 80301 USA > >>> phone: 303-417-1345 x110 > >>> email: david.vanhorn@backcountryaccess.com > >>> > >> -- > >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 > >> View/change your membership options at=20 > >> http://mailman.mit.edu/mailman/listinfo/piclist > >> > > > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 > > View/change your membership options at=20 > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 > > View/change your membership options at=20 > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 > View/change your membership options at=20 > http://mailman.mit.edu/mailman/listinfo/piclist > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 > View/change your membership options at=20 > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclis= t --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .