ULN2803 ok to be driven by 3.3V logic?
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From: Joerg on 8 Jan 2010 18:08 Jim Thompson wrote: > On Fri, 08 Jan 2010 13:40:56 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> Nico Coesel wrote: >>> Joerg <invalid(a)invalid.invalid> wrote: >>> >>>> John Larkin wrote: >>>>> On Thu, 07 Jan 2010 14:27:59 -0800, Joerg <invalid(a)invalid.invalid> >>>>> wrote: >>>>> >>>>>> Jim Thompson wrote: >>>>>>> On Thu, 07 Jan 2010 13:20:52 -0800, 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? >>>>>>>> >>>>>>>> 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 :-) >>>>>>> Should work just fine. >>>>>>> >>>>>>>> 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. >>>>>>> I'm quite surprised there isn't a MOS version. >>>>>>> >>>>>> So am I. There are some but with boutique pricing. Not surprisingly many >>>>>> of them didn't make it in the marketplace because guys like me wouldn't >>>>>> use them. Here is a decoder type which can be used in "memory mode", and >>>>>> it also went to lalaland: >>>>>> >>>>>> http://www.allegromicro.com/en/Products/Part_Numbers/6259/6259.pdf >>>>>> >>>>>> >>>>>>> I don't keep track of off-the-shelf stuff. Have you looked at >>>>>>> open-drain buffers/inverters? >>>>>>> >>>>>> Yeah, they are either too wimpy or way more expensive than two dozen >>>>>> discrete parts. This time I need to drive relays with up to 60mA coil >>>>>> current each. >>>>> 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. >>>>> >>>> A buck fifty wouldn't fly in this case, serial would work well though. >>>> However, I have (almost) been burned by TPIC parts in the past, by part >>>> obsolescence. Somehow I had a hunch and chickened out. Now I am glad I >>>> did. But this one is cool if you have the budget and it's been around >>>> for almost two decades. If anyone is interested: >>>> >>>> http://focus.ti.com/lit/ds/symlink/tpic6595.pdf >>> ST has some equivalents so thats not bad. IMHO this series of chips >>> have become an industry standard like the NE555, ULN2003 and the 8051. >>> >> But for that they would have to be << 50 cents :-) > > Cheapskate ;-) > When it comes to circuit design I am, when it comes to beer, wine and cheese then I am not :-) Once I had an inductor in a design and it cost something like a buck sixty. Was quite happy that I got away with that one by upping a switcher frequency. While talking with the client they asked whether there would possibly be a cheaper inductor. Remember when some guys here thought I was nuts for suggesting that resistors other than 1% are still useful? An assembler in China once sent a formal request via my client, to identify those that could be increased from 10% to 20%. That is not a joke. 15 minutes of billed time later they had the list. Don't remember exactly but I believe it saved something like 30 bucks. Per month, and it's now 15 years and counting ... -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Mark Zenier on 8 Jan 2010 15:57 In article <7qn1htFchdU1(a)mid.individual.net>, Joerg <news(a)analogconsultants.com> 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? > >http://focus.ti.com/lit/ds/symlink/uln2803a.pdf >http://www.toshiba.com/taec/components2/Datasheet_Sync//393/22738.pdf > So, get some ULN-2805A. Or ULN-2801 and pick your own input resistors. ;-) A graph of Iin vs. Vin for the '03, in the 22 year old Sprague datasheet, shows the normal operating range is expected to be about 2 1/3 and about 3 2/3 volts. Giving an input current of .5 to 1.25 mA. TTL Voh was pretty limp, so CMOS at 3.3 can't be much worse. Mark Zenier mzenier(a)eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)
From: Joerg on 9 Jan 2010 16:01 Mark Zenier wrote: > In article <7qn1htFchdU1(a)mid.individual.net>, > Joerg <news(a)analogconsultants.com> 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? >> >> http://focus.ti.com/lit/ds/symlink/uln2803a.pdf >> http://www.toshiba.com/taec/components2/Datasheet_Sync//393/22738.pdf >> > > So, get some ULN-2805A. Or ULN-2801 and pick your own input resistors. ;-) > Thanks, Mark. However, Digikey has only DIP and stock on the first one is zero, very low on the second one. That always gives me the goose bumps. > A graph of Iin vs. Vin for the '03, in the 22 year old Sprague datasheet, > shows the normal operating range is expected to be about 2 1/3 and > about 3 2/3 volts. Giving an input current of .5 to 1.25 mA. > > TTL Voh was pretty limp, so CMOS at 3.3 can't be much worse. > Yep, that's right, old TTL never went much past 3V. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Gerhard on 11 Jan 2010 12:18
"Joerg" <invalid(a)invalid.invalid> wrote in message news:7qs94iFvt0U3(a)mid.individual.net... > Mark Zenier wrote: >> In article <7qn1htFchdU1(a)mid.individual.net>, >> Joerg <news(a)analogconsultants.com> 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? >>> >>> http://focus.ti.com/lit/ds/symlink/uln2803a.pdf >>> http://www.toshiba.com/taec/components2/Datasheet_Sync//393/22738.pdf >>> >> >> So, get some ULN-2805A. Or ULN-2801 and pick your own input resistors. >> ;-) > > Thanks, Mark. However, Digikey has only DIP and stock on the first one is > zero, very low on the second one. That always gives me the goose bumps. > > >> A graph of Iin vs. Vin for the '03, in the 22 year old Sprague datasheet, >> shows the normal operating range is expected to be about 2 1/3 and >> about 3 2/3 volts. Giving an input current of .5 to 1.25 mA. >> >> TTL Voh was pretty limp, so CMOS at 3.3 can't be much worse. >> > > Yep, that's right, old TTL never went much past 3V. > > -- > Regards, Joerg > > http://www.analogconsultants.com/ > Driving ULN2803 from 3.3V might be OK for most micros and logic. Be careful with the 8051/2 as the P1 P2 and P3 outputs have very limited high drive (essentially -60uA at Vcc -1.5). The On Semiconductor NUD31XX series 'Industrial Inductive Load Drivers' (comes in singels and duals) are especially suited for relays and other inductive loads. The NUD31XX devices come with 5V, 12V, 24V and 60V inductive protected outputs. Continuous output current sink varies from about 500mA (5V) to 150mA (60V) depending on the Vgs available and Vds that can be tolerated. Their low threshold (2V5 fully on) FET inputs should work with most 3.3v logic and micros. A bit pricy at +- $0.37 each per 100 for the dual devices. For detail see: http://www.onsemi.com/PowerSolutions/search.do?searchString=NUD31&searchType=others&tabbed=Y&clearFilters=Y (go to www.onsemi.com and search for NUD31 if URL wrap causes a problem) Most of these are available from Mouser. Search for 'NUD31' to see price and availability of the series. Another option might be to look at biased transistors available at 0.03 each or less. Board populating cost might offset the low device cost. Biased transistors would however require an inductive protection diode and input drive might be a problem. (3 to 5 mA input for the 60mA output required). I often find biased transistors cost effective due to lower assembly costs. For Joerg's application the ULN2803s seems to be the most cost effective solution. Gerhard van den Berg CSIR |