ULN2803 ok to be driven by 3.3V logic?
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From: Nico Coesel on 8 Jan 2010 13:46 Joerg <invalid(a)invalid.invalid> wrote: >Gents, > >Have to drive a bucket full of 12V relays but the uC is only 3.3V. The >ULN2803 is touted as a driver for 5V TTL logic by most companies (like >TI) but datasheets hint that it can happily live down to around 3V drive >level. Is that kosher? I never had problems driving it with 3.3V. Its a darlington array after all. Not mosfets. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico(a)nctdevpuntnl (punt=.) --------------------------------------------------------------
From: Nico Coesel on 8 Jan 2010 13:50 Joerg <invalid(a)invalid.invalid> wrote: >Joe G (Home) wrote: >> "Joerg" <invalid(a)invalid.invalid> wrote in message >> news:7qn1htFchdU1(a)mid.individual.net... >>> Gents, >>> >>> Have to drive a bucket full of 12V relays but the uC is only 3.3V. The >>> ULN2803 is touted as a driver for 5V TTL logic by most companies (like TI) >>> but datasheets hint that it can happily live down to around 3V drive >>> level. Is that kosher? >>> >>> http://focus.ti.com/lit/ds/symlink/uln2803a.pdf >>> http://www.toshiba.com/taec/components2/Datasheet_Sync//393/22738.pdf >>> >>> App note SLAA148 suggests it is kosher but ... I figure I'd better ask the >>> famous gurus in this here group :-) >>> >>> http://focus.ti.com/lit/an/slaa148/slaa148.pdf >>> >>> A FET version would be nice as it gets the outputs lower but that's only >>> available from the more boutiquish suppliers. Demasiados Dolares, as >>> usual. >>> >>> -- >>> Regards, Joerg >>> >> Infineon SPIDER Driver IC's - Multi channel SPI Driver? >> >> See here http://bit.ly/5xVmH8 >> > >Thanks. However, it costs almost two bucks in qties and Digikey has no >stock (which is always a red flag for me). Yikes. That's almost ten >times the cost of the ULN parts, not a chance. What were they thinking? > > >> Parallel and Serial Isolated ISOFACE Driver? >> http://bit.ly/5GrCFF >> > >Those are very nice indeed when you need isolation (I often do). But >also non-stock and they'd have to compete with the usual optocoupler >plus driver solution. Considering that they want $6 for them that'll be >a tall order for their sales guys. > >I wish Infineon would come off their key account thinking and stuff the >channels, such as Digikey. And adjust their pricing. Their R&D develops >top notch products but I often shun them because of past purchasing >problems. The first thing Infineon needs to do is learn how to write datasheets. Back in my design-stuff-for-telecom days I noticed Zarlink (formerly Mitel) could explain the same in 20 pages where Infineon needed 200 pages to explain nothing at all. Guess what made it to the PCB. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico(a)nctdevpuntnl (punt=.) --------------------------------------------------------------
From: Nico Coesel on 8 Jan 2010 13:52 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Thu, 07 Jan 2010 14:27:59 -0800, Joerg <invalid(a)invalid.invalid> >wrote: > > >TPIC6595 is cool, serial in and eight fet drains out, but it needs 5 >volts. We're using them to drive a lot of relays. Those also work at 3.3V. There is an appnote from TI. I don't know about the second source version from (IIRC) ST though. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico(a)nctdevpuntnl (punt=.) --------------------------------------------------------------
From: Spehro Pefhany on 8 Jan 2010 14:09 On Fri, 08 Jan 2010 18:46:42 GMT, nico(a)puntnl.niks (Nico Coesel) wrote: >Joerg <invalid(a)invalid.invalid> wrote: > >>Gents, >> >>Have to drive a bucket full of 12V relays but the uC is only 3.3V. The >>ULN2803 is touted as a driver for 5V TTL logic by most companies (like >>TI) but datasheets hint that it can happily live down to around 3V drive >>level. Is that kosher? > >I never had problems driving it with 3.3V. Its a darlington array >after all. Not mosfets. It should be fine-- "5V" TTL has output voltage in the 3.3V range when sourcing current, but I'd get nervous if driving a lot of output current and the nominal supply is less than 3.3V. I have not been able to use them in some cases because the output voltage drop is too high (Darlington). A CMOS version with low Rds(on) would be nice, but it has to be really cheap (the bipolar 7-output ULN2003A is under a dime).
From: Joerg on 8 Jan 2010 14:12
Nico Coesel wrote: > Joerg <invalid(a)invalid.invalid> wrote: > >> Gents, >> >> Have to drive a bucket full of 12V relays but the uC is only 3.3V. The >> ULN2803 is touted as a driver for 5V TTL logic by most companies (like >> TI) but datasheets hint that it can happily live down to around 3V drive >> level. Is that kosher? > > I never had problems driving it with 3.3V. Its a darlington array > after all. Not mosfets. > Thanks. I was just wondering about resistor tolerances in there, can be quite high in chips. But the datasheet sez ok and you plus others also said it, so that gives me the warm and fuzzy about it. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |