josephkk wrote:> On Wed, 26 Jun 2013 07:52:30 -0700, Joerg <invalid@invalid.invalid> wrote: > >>>>>> If they say 5.8V, what's you gut feel it could really take if a surge or >>>>>> pulse salvo of a few msec comes through? It's amplitude would be >>>>>> slightly over 7V. because it leans into protective diodes we have up >>>>>> front of the uC port. Those are regular Si-diodes against the 5V rail >>>>>> and GND. >>>>> DC over-voltage is a no-no... ESD only. >>>>> >>>> DC will never exceed 5V and abs max is 5.8V. So you think ESD or surges >>>> (the usual machine-gun style bursts in EMC tests) are ok? We have it >>>> clamped to a 5V rail but it could really lean into those clamp diodes. >>> This thread rattles around avoiding specifics. Is the "5V-tolerant" >>> input an input that has 3.3V as VDD? >>> >> Yes, it is, that's what I wrote in the original post :-) >> >> The uC has only a 3.3V supply, no 5V supply. But some lines coming in >> are from logic that is on 5V, so can't be ESD-clamped lower than 5V. > > Well, Jeorg you could use two stage protection; say 50 ohms then a 5.6 V > zener to ground, then another 100 ohms and a 5.1 or even 4.7 volt zener > to ground. Either way, you have to decide. >Way too little room for that, otherwise we'd have clamped them all through intermediate 3.3V rail diodes. It's one of those super-tight boards. -- Regards, Joerg http://www.analogconsultants.com/
8051F020 series, 5V tolerant input schematic?
Started by ●June 25, 2013
Reply by ●June 27, 20132013-06-27
Reply by ●June 27, 20132013-06-27
On Thu, 27 Jun 2013 12:15:39 -0700, John Larkin <jlarkin@highlandtechnology.com> wrote:>On Thu, 27 Jun 2013 11:51:54 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>On Thu, 27 Jun 2013 11:33:20 -0700, Jim Thompson >><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >> >>>On Thu, 27 Jun 2013 11:15:45 -0700, John Larkin >>><jlarkin@highlandtechnology.com> wrote: >>> >>>>On Wed, 26 Jun 2013 17:36:11 -0700, Jim Thompson >>>><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >>>> >>>>>On Wed, 26 Jun 2013 14:31:11 -0700, John Larkin >>>>><jlarkin@highlandtechnology.com> wrote: >>[snip] >>>>>> >>>>>>Likely a bad PCB design. Did you do it? >>>>> >>>>>Learn to read... your comprehension is REALLY BAD... "confounding the >>>>>FAE, and, now, the factory" >>>>> >>>>> ...Jim Thompson >>>> >>>>And you, too. >>>> >>>>Who did the PCB? Is it an eval board? >>> >>>I'm not sure. The work was done in Auckland, NZ, by my client, not by >>>me, I don't do PCB's, I only do chips... and my 64-channel LED driver >>>is working gorgeously. >>> >>>FAE == LT Field Application Engineer... he couldn't figure out the >>>problem... it was built exactly to the data sheet. Problem sent off >>>to the factory, who, 4 months later, still haven't resolved the issue. >>> >>>I was asked to simulate it on LTspice, which I did, and the simulator >>>says it works... actuality says it doesn't. >>> >>>> >>>>What part is it? What's the problem? >>> >>>LTC3853, oscillates/loop-instability; running as 3-phase >>>single-output. >>> >>> ...Jim Thompson >> >>Adding a point... the part is peddled as a 3-output device, but the >>application note shows 3-phase single-output operation. I suspect >>this was just thrown onto the data sheet without physical testing, >>just simulation of a _behavioral_ model >:-} >> >> ...Jim Thompson > >Those multiphase slope-compensated things are prone to all sorts of >loop funnies, including sub-cycle oscillation. Cap ESR matters a lot. > >Running at higher frequency sometimes helps. > >Is the problem on an eval board, or a new design?John, I don't know the particulars, I was just thrown into the mix to run an LTspice simulation... otherwise I know not much. All I know is that the problem flummoxed the FAE, and the factory has gone silent on us. I can find out more next week when I meet again with the principals. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●June 27, 20132013-06-27
Joerg <invalid@invalid.invalid> wrote:> Way too little room for that, otherwise we'd have clamped them all > through intermediate 3.3V rail diodes. It's one of those super-tight > boards.How do you end up in that position? Is there no way to increase the size of the board when it gets over 90% or so? It is very difficult to route a tightly-packed pcb, so it costs more. Is the enclosure the limiting factor? If so, is it possible to split the board in two and double the available space? This would increase the chance of coming up with and new idea that could vastly increase the value of the product. But when your mind knows a pcb is 99% full, you automatically discard any new ideas because there is no room. I am amazed at the number of times you and JL mention you cannot use some solution to a problem because there is not enough room.
Reply by ●June 28, 20132013-06-28
On Thu, 27 Jun 2013 16:22:28 -0700, Joerg <invalid@invalid.invalid> = wrote:>josephkk wrote: >> On Wed, 26 Jun 2013 07:52:30 -0700, Joerg <invalid@invalid.invalid> =wrote:>>=20 >>>>>>> If they say 5.8V, what's you gut feel it could really take if a =surge or>>>>>>> pulse salvo of a few msec comes through? It's amplitude would be >>>>>>> slightly over 7V. because it leans into protective diodes we have=up>>>>>>> front of the uC port. Those are regular Si-diodes against the 5V =rail>>>>>>> and GND. >>>>>> DC over-voltage is a no-no... ESD only. >>>>>> =09 >>>>> DC will never exceed 5V and abs max is 5.8V. So you think ESD or =surges>>>>> (the usual machine-gun style bursts in EMC tests) are ok? We have =it>>>>> clamped to a 5V rail but it could really lean into those clamp =diodes.>>>> This thread rattles around avoiding specifics. Is the "5V-tolerant" >>>> input an input that has 3.3V as VDD? >>>> =09 >>> Yes, it is, that's what I wrote in the original post :-) >>> >>> The uC has only a 3.3V supply, no 5V supply. But some lines coming in >>> are from logic that is on 5V, so can't be ESD-clamped lower than 5V. >>=20 >> Well, Jeorg you could use two stage protection; say 50 ohms then a 5.6=V>> zener to ground, then another 100 ohms and a 5.1 or even 4.7 volt =zener>> to ground. Either way, you have to decide. >>=20 > >Way too little room for that, otherwise we'd have clamped them all >through intermediate 3.3V rail diodes. It's one of those super-tight =boards. Perhaps you need to tell them to give you the space you need or got h***. ?-)
Reply by ●June 28, 20132013-06-28
JW wrote:> Joerg <invalid@invalid.invalid> wrote: > >> Way too little room for that, otherwise we'd have clamped them all >> through intermediate 3.3V rail diodes. It's one of those super-tight >> boards. > > How do you end up in that position? ...Usually through the telephone, "Yo, George, can you help us get this through cert?".> ... Is there no way to increase the size of > the board when it gets over 90% or so? ...Absolutamente no :-(> ... It is very difficult to route a tightly-packed pcb, so it costs more. > > Is the enclosure the limiting factor? If so, is it possible to split the > board in two and double the available space? This would increase the chance > of coming up with and new idea that could vastly increase the value of the > product. But when your mind knows a pcb is 99% full, you automatically > discard any new ideas because there is no room. >No chance, it's an existing and very tight unit. Sometimes they have to be that way, earlier this year I designed something similar but way different market. Even when dropping to 0402 it barely fit.> I am amazed at the number of times you and JL mention you cannot use some > solution to a problem because there is not enough room. >Comes with the nature of our turf. I design a lot of sensor stuff and that has to live in crammed quarters. Same for aerospace, there you typically get told "We have this much volume, here are the dimensions, and we need something that is xx percent better than what the competition has". Think about it like a retrofit market. For example, if you designed a new fancy timer/dimmer/whatever, it would still have to fit in the standard North American NEMA box. If it didn't you could not sell it. Now multiply that by 0.1 :-) -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●June 28, 20132013-06-28
josephkk wrote:> On Thu, 27 Jun 2013 16:22:28 -0700, Joerg <invalid@invalid.invalid> wrote: > >> josephkk wrote: >>> On Wed, 26 Jun 2013 07:52:30 -0700, Joerg <invalid@invalid.invalid> wrote: >>> >>>>>>>> If they say 5.8V, what's you gut feel it could really take if a surge or >>>>>>>> pulse salvo of a few msec comes through? It's amplitude would be >>>>>>>> slightly over 7V. because it leans into protective diodes we have up >>>>>>>> front of the uC port. Those are regular Si-diodes against the 5V rail >>>>>>>> and GND. >>>>>>> DC over-voltage is a no-no... ESD only. >>>>>>> >>>>>> DC will never exceed 5V and abs max is 5.8V. So you think ESD or surges >>>>>> (the usual machine-gun style bursts in EMC tests) are ok? We have it >>>>>> clamped to a 5V rail but it could really lean into those clamp diodes. >>>>> This thread rattles around avoiding specifics. Is the "5V-tolerant" >>>>> input an input that has 3.3V as VDD? >>>>> >>>> Yes, it is, that's what I wrote in the original post :-) >>>> >>>> The uC has only a 3.3V supply, no 5V supply. But some lines coming in >>>> are from logic that is on 5V, so can't be ESD-clamped lower than 5V. >>> Well, Jeorg you could use two stage protection; say 50 ohms then a 5.6 V >>> zener to ground, then another 100 ohms and a 5.1 or even 4.7 volt zener >>> to ground. Either way, you have to decide. >>> >> Way too little room for that, otherwise we'd have clamped them all >> through intermediate 3.3V rail diodes. It's one of those super-tight boards. > > Perhaps you need to tell them to give you the space you need or got h***. >Not sure what the last word should mean but no, this is a normal situation. I see things like that several times a year. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●June 28, 20132013-06-28
Joerg <invalid@invalid.invalid> wrote:> Comes with the nature of our turf. I design a lot of sensor stuff and > that has to live in crammed quarters. Same for aerospace, there you > typically get told "We have this much volume, here are the dimensions, > and we need something that is xx percent better than what the > competition has". > > Think about it like a retrofit market. For example, if you designed a > new fancy timer/dimmer/whatever, it would still have to fit in the > standard North American NEMA box. If it didn't you could not sell it. > Now multiply that by 0.1 :-) >Very good answer. Thanks!
Reply by ●June 28, 20132013-06-28
Joerg <invalid@invalid.invalid> wrote:>josephkk wrote: >> On Wed, 26 Jun 2013 07:52:30 -0700, Joerg <invalid@invalid.invalid> wrote: >> >>>>>>> If they say 5.8V, what's you gut feel it could really take if a surge or >>>>>>> pulse salvo of a few msec comes through? It's amplitude would be >>>>>>> slightly over 7V. because it leans into protective diodes we have up >>>>>>> front of the uC port. Those are regular Si-diodes against the 5V rail >>>>>>> and GND. >> >> Well, Jeorg you could use two stage protection; say 50 ohms then a 5.6 V >> zener to ground, then another 100 ohms and a 5.1 or even 4.7 volt zener >> to ground. Either way, you have to decide. >> > >Way too little room for that, otherwise we'd have clamped them all >through intermediate 3.3V rail diodes. It's one of those super-tight boards.I've moved away from diodes to the rail. Many regulators can't sink current and there is always chance on injecting noise into the supply lines. I've used these low leakage zener diodes to improve a design recently: http://www.nxp.com/documents/data_sheet/BZB984_SERIES.pdf -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
Reply by ●June 28, 20132013-06-28
Nico Coesel wrote:> Joerg <invalid@invalid.invalid> wrote: > >> josephkk wrote: >>> On Wed, 26 Jun 2013 07:52:30 -0700, Joerg <invalid@invalid.invalid> wrote: >>> >>>>>>>> If they say 5.8V, what's you gut feel it could really take if a surge or >>>>>>>> pulse salvo of a few msec comes through? It's amplitude would be >>>>>>>> slightly over 7V. because it leans into protective diodes we have up >>>>>>>> front of the uC port. Those are regular Si-diodes against the 5V rail >>>>>>>> and GND. >>> Well, Jeorg you could use two stage protection; say 50 ohms then a 5.6 V >>> zener to ground, then another 100 ohms and a 5.1 or even 4.7 volt zener >>> to ground. Either way, you have to decide. >>> >> Way too little room for that, otherwise we'd have clamped them all >> through intermediate 3.3V rail diodes. It's one of those super-tight boards. > > I've moved away from diodes to the rail. Many regulators can't sink > current and there is always chance on injecting noise into the supply > lines. >You need a shunt that kicks in if the rail wants to ride up. Only an issue if the total load on the rail has phases where it is very light. Noise isn't an issue because there is usually lots of capacitance on a rail and the diodes are only for major ESD events and such.> I've used these low leakage zener diodes to improve a design recently: > http://www.nxp.com/documents/data_sheet/BZB984_SERIES.pdf >Zeners are nice but for many digital circuits the 5% tolerance is too much. Like the 5V6 in the datasheet which at 5mA can be anywhere between 5.2V and 6V. The datasheet is a bit skimpy, doesn't say what happens if a pulse of half an amp comes along. Will it go to 7V? More? Probably a lot more when looking at the differential resistance at 5mA. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●June 28, 20132013-06-28
On Friday, June 28, 2013 6:44:07 PM UTC+2, Nico Coesel wrote:> Joerg <invalid@invalid.invalid> wrote: > > > > >josephkk wrote: > > >> On Wed, 26 Jun 2013 07:52:30 -0700, Joerg <invalid@invalid.invalid> wrote: > > >> > > >>>>>>> If they say 5.8V, what's you gut feel it could really take if a surge or > > >>>>>>> pulse salvo of a few msec comes through? It's amplitude would be > > >>>>>>> slightly over 7V. because it leans into protective diodes we have up > > >>>>>>> front of the uC port. Those are regular Si-diodes against the 5V rail > > >>>>>>> and GND. > > >> > > >> Well, Jeorg you could use two stage protection; say 50 ohms then a 5.6 V > > >> zener to ground, then another 100 ohms and a 5.1 or even 4.7 volt zener > > >> to ground. Either way, you have to decide. > > >> > > > > > >Way too little room for that, otherwise we'd have clamped them all > > >through intermediate 3.3V rail diodes. It's one of those super-tight boards. > > > > I've moved away from diodes to the rail. Many regulators can't sink > > current and there is always chance on injecting noise into the supply > > lines. > > > > I've used these low leakage zener diodes to improve a design recently: > > http://www.nxp.com/documents/data_sheet/BZB984_SERIES.pdf >we use PESD3V3L4UG quad esd zeners in a sot353 and resistor arrays maybe something like NUF6010MU ? -Lasse
