On 2018-01-19 20:22, John Larkin wrote:> On Fri, 19 Jan 2018 20:21:36 -0500, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> On 01/19/2018 08:11 PM, John Larkin wrote: >>> On Fri, 19 Jan 2018 19:28:48 -0500, bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> On 01/19/2018 06:32 PM, Joerg wrote: >>>>> Attention, highly non-political post. >>>>> >>>>> Here is a puzzler. This ST datasheet says on page 5 that the junction to >>>>> ambient temp rise is 55C/W for SO8 and 115C/W for SOT89: >>>>> >>>>> https://media.digikey.com/pdf/Data%20Sheets/ST%20Microelectronics%20PDFS/L79L.pdf >>>>> >>>>> >>>>> This TI datasheet for the positive regulator states pretty much the >>>>> opposite on page 4: >>>>> >>>>> http://www.ti.com/lit/ds/symlink/ua78l.pdf >>>>> >>>>> One is a negative and one a positive regulator which shouldn't make much >>>>> of a difference as I assume they calculated with similar copper. So it >>>>> seems one of them may be wrong. Question is, which one? >>>>> >>>> >>>> Doesn't make much sense to have a junction to ambient thermal resistance >>>> _lower_ than the junction to case, does it? >>>> >>>> I think they vertically transposed the top right two cells in the grid >>>> on page 4 of the ua78l datasheetMaybe they let some intern do that.>>> >>> Someone could maybe make a business out of proofing data sheets. >> >> Why pay for it when one's customers apparently so willingly do it for >> free? :D :D :D > > But the errors are rarely fixed, after years and decades. >That's why people don't even report it anymore. -- Regards, Joerg http://www.analogconsultants.com/
SO8 versus SOT89 junction to ambient?
Started by ●January 19, 2018
Reply by ●January 20, 20182018-01-20
Reply by ●January 20, 20182018-01-20
On 01/20/2018 10:15 AM, Joerg wrote:> Maybe they let some intern do that. > >>>> >>>> Someone could maybe make a business out of proofing data sheets. >>> >>> Why pay for it when one's customers apparently so willingly do it for >>> free? :D :D :D >> >> But the errors are rarely fixed, after years and decades. >> > > That's why people don't even report it anymore.Company X claims their datasheets are perfect even when they're not, Company Y accepts corrections from users and makes regular fixes. Customer looks thru the list of all the bug-fixes on Company Y's revision page and thinks "Ugh, these guys don't know what they're doing." Company X smiles and say "We stand by the accuracy of our documentation." User thinks "Great! I'll go with Company X." User encounters a serious problem in Company X's documentation. Already being invested in the choice, user works hard to rationalize the mistake to actually being their own fault. Company X stands by the accuracy of their documentation, after all.
Reply by ●January 20, 20182018-01-20
On 2018-01-20 07:30, bitrex wrote:> On 01/20/2018 10:15 AM, Joerg wrote: > >> Maybe they let some intern do that. >> >>>>> >>>>> Someone could maybe make a business out of proofing data sheets. >>>> >>>> Why pay for it when one's customers apparently so willingly do it for >>>> free? :D :D :D >>> >>> But the errors are rarely fixed, after years and decades. >>> >> >> That's why people don't even report it anymore. > > Company X claims their datasheets are perfect even when they're not, > Company Y accepts corrections from users and makes regular fixes. > > Customer looks thru the list of all the bug-fixes on Company Y's > revision page and thinks "Ugh, these guys don't know what they're > doing." Company X smiles and say "We stand by the accuracy of > our documentation." > > User thinks "Great! I'll go with Company X." User encounters a > serious problem in Company X's documentation. Already being invested > in the choice, user works hard to rationalize the mistake to actually > being their own fault. Company X stands by the accuracy of their > documentation, after all. >Alternative scenario at yours truly: Company X gets blacklisted and remains on that blacklist for a few decades. They won't ever know how much revenue went elsewhere because the user never communicates with them anymore. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●January 20, 20182018-01-20
On Friday, January 19, 2018 at 6:31:53 PM UTC-5, Joerg wrote:> Attention, highly non-political post. > > Here is a puzzler. This ST datasheet says on page 5 that the junction to > ambient temp rise is 55C/W for SO8 and 115C/W for SOT89: > > https://media.digikey.com/pdf/Data%20Sheets/ST%20Microelectronics%20PDFS/L79L.pdfExplained by two footnotes-- "(1) Our SO-8 package used for Voltage Regulators is modified internally to have pins 2, 3, 6 and 7 electrically communed to the die attach flag. This particular frame decreases the total thermal resistance of the package and increases its ability to dissipate power when an appropriate area of copper on the printed circuit board is available for heat-sinking. The external dimensions are the same as for the standard SO-8." "RthJA Thermal resistance junction-ambient (Max) 55 (1) 200 115 °C/W ==> Notes: (1) ***Considering 6 cm^2 of copper Board heat-sink.***" <===> This TI datasheet for the positive regulator states pretty much the > opposite on page 4: > > http://www.ti.com/lit/ds/symlink/ua78l.pdf > > One is a negative and one a positive regulator which shouldn't make much > of a difference as I assume they calculated with similar copper. So it > seems one of them may be wrong. Question is, which one?Cheers, James Arthur
Reply by ●January 20, 20182018-01-20
Den lørdag den 20. januar 2018 kl. 01.28.53 UTC+1 skrev bitrex:> On 01/19/2018 06:32 PM, Joerg wrote: > > Attention, highly non-political post. > > > > Here is a puzzler. This ST datasheet says on page 5 that the junction to > > ambient temp rise is 55C/W for SO8 and 115C/W for SOT89: > > > > https://media.digikey.com/pdf/Data%20Sheets/ST%20Microelectronics%20PDFS/L79L.pdf > > > > > > This TI datasheet for the positive regulator states pretty much the > > opposite on page 4: > > > > http://www.ti.com/lit/ds/symlink/ua78l.pdf > > > > One is a negative and one a positive regulator which shouldn't make much > > of a difference as I assume they calculated with similar copper. So it > > seems one of them may be wrong. Question is, which one? > > > > Doesn't make much sense to have a junction to ambient thermal resistance > _lower_ than the junction to case, does it?it might be possible, if the junction to plastic case is seen in isolation and the junction to ambient is solder to some area of copper
Reply by ●January 20, 20182018-01-20
On 2018-01-20 09:08, dagmargoodboat@yahoo.com wrote:> On Friday, January 19, 2018 at 6:31:53 PM UTC-5, Joerg wrote: >> Attention, highly non-political post. >> >> Here is a puzzler. This ST datasheet says on page 5 that the junction to >> ambient temp rise is 55C/W for SO8 and 115C/W for SOT89: >> >> https://media.digikey.com/pdf/Data%20Sheets/ST%20Microelectronics%20PDFS/L79L.pdf > > Explained by two footnotes-- > > "(1) Our SO-8 package used for Voltage Regulators is modified internally > to have pins 2, 3, 6 and 7 electrically communed to the die attach flag. > This particular frame decreases the total thermal resistance of the package > and increases its ability to dissipate power when an appropriate area of > copper on the printed circuit board is available for heat-sinking. The > external dimensions are the same as for the standard SO-8." > > > "RthJA Thermal resistance junction-ambient (Max) 55 (1) 200 115 °C/W > > ==> Notes: (1) ***Considering 6 cm^2 of copper Board heat-sink.***" <=== >That's fine but an apples to apples comparison will also provide 6cm^2 for the SOT89. Nobody in their right mind would mount them without serious copper area if heavily loaded. [...] -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●January 20, 20182018-01-20
On Saturday, January 20, 2018 at 2:35:48 PM UTC-5, Joerg wrote:> On 2018-01-20 09:08, dagmargoodboat@yahoo.com wrote: > > On Friday, January 19, 2018 at 6:31:53 PM UTC-5, Joerg wrote: > >> Attention, highly non-political post. > >> > >> Here is a puzzler. This ST datasheet says on page 5 that the junction to > >> ambient temp rise is 55C/W for SO8 and 115C/W for SOT89: > >> > >> https://media.digikey.com/pdf/Data%20Sheets/ST%20Microelectronics%20PDFS/L79L.pdf > > > > Explained by two footnotes-- > > > > "(1) Our SO-8 package used for Voltage Regulators is modified internally > > to have pins 2, 3, 6 and 7 electrically communed to the die attach flag. > > This particular frame decreases the total thermal resistance of the package > > and increases its ability to dissipate power when an appropriate area of > > copper on the printed circuit board is available for heat-sinking. The > > external dimensions are the same as for the standard SO-8." > > > > > > "RthJA Thermal resistance junction-ambient (Max) 55 (1) 200 115 °C/W > > > > ==> Notes: (1) ***Considering 6 cm^2 of copper Board heat-sink.***" <=== > > > > That's fine but an apples to apples comparison will also provide 6cm^2 > for the SOT89. Nobody in their right mind would mount them without > serious copper area if heavily loaded. > > [...] > > -- > Regards, Joerg > > http://www.analogconsultants.com/From ST's numbers, the SOT89 with the same heatsink would have RthJA of 50°C/W, 5°C/W better than the SO-8 package. It's hard to beat a solid copper tab. Cheers, James Arthur
Reply by ●January 20, 20182018-01-20
On 2018-01-20 11:42, dagmargoodboat@yahoo.com wrote:> On Saturday, January 20, 2018 at 2:35:48 PM UTC-5, Joerg wrote: >> On 2018-01-20 09:08, dagmargoodboat@yahoo.com wrote: >>> On Friday, January 19, 2018 at 6:31:53 PM UTC-5, Joerg wrote: >>>> Attention, highly non-political post. >>>> >>>> Here is a puzzler. This ST datasheet says on page 5 that the junction to >>>> ambient temp rise is 55C/W for SO8 and 115C/W for SOT89: >>>> >>>> https://media.digikey.com/pdf/Data%20Sheets/ST%20Microelectronics%20PDFS/L79L.pdf >>> >>> Explained by two footnotes-- >>> >>> "(1) Our SO-8 package used for Voltage Regulators is modified internally >>> to have pins 2, 3, 6 and 7 electrically communed to the die attach flag. >>> This particular frame decreases the total thermal resistance of the package >>> and increases its ability to dissipate power when an appropriate area of >>> copper on the printed circuit board is available for heat-sinking. The >>> external dimensions are the same as for the standard SO-8." >>> >>> >>> "RthJA Thermal resistance junction-ambient (Max) 55 (1) 200 115 °C/W >>> >>> ==> Notes: (1) ***Considering 6 cm^2 of copper Board heat-sink.***" <=== >>> >> >> That's fine but an apples to apples comparison will also provide 6cm^2 >> for the SOT89. Nobody in their right mind would mount them without >> serious copper area if heavily loaded. >> >> [...] >> >> -- >> Regards, Joerg >> >> http://www.analogconsultants.com/ > > From ST's numbers, the SOT89 with the same heatsink would have > RthJA of 50°C/W, 5°C/W better than the SO-8 package. > > It's hard to beat a solid copper tab. >I only see 115C/W for the SOT89 in table 2. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●January 20, 20182018-01-20
On Fri, 19 Jan 2018 15:57:08 -0800, Joerg <news@analogconsultants.com> wrote:>On 2018-01-19 15:45, John Larkin wrote: >> On Fri, 19 Jan 2018 15:32:00 -0800, Joerg <news@analogconsultants.com> >> wrote: >> >>> Attention, highly non-political post. >>> >>> Here is a puzzler. This ST datasheet says on page 5 that the junction to >>> ambient temp rise is 55C/W for SO8 and 115C/W for SOT89: >>> >>> https://media.digikey.com/pdf/Data%20Sheets/ST%20Microelectronics%20PDFS/L79L.pdf >> >> Looks like they heat-sunk the SO8 but maybe didn't the SOT89. >> > >That would be a major flaw in a datasheet. It's just puzzling that the >data is almost exactly opposite between the two. > >Datasheets these days ain't what they use to be. I just had to fire off >another support request because the AD8337 datasheet merely says to >connect the pad "to the PCB". Great. To GND? The negative rails? They >forgot ... > > >>> >>> This TI datasheet for the positive regulator states pretty much the >>> opposite on page 4: >>> >>> http://www.ti.com/lit/ds/symlink/ua78l.pdf >>> >>> One is a negative and one a positive regulator which shouldn't make much >>> of a difference as I assume they calculated with similar copper. So it >>> seems one of them may be wrong. Question is, which one? >> >> Unless the SO8 has a power pad, the SOT89, soldered to some copper, >> should win. >> > >All they have on the SO8 is that the four center pins go to the >respective plane (GND on the positive regulator and VIN on the negative >one). > > >> I've dissipated 3 watts from a SOT89 soldered to a copper pour. >> >> https://www.dropbox.com/s/rkg3jkzvqutl822/DSC01850.JPG?raw=1 >> >> https://www.dropbox.com/s/iy5gyxjvgi14sf1/DSC01857.JPG?raw=1 >> >> Thermal vias could make this better. >> > >Good words of wisdom. I'll stay with SOT89 then. That is what I used >before and while they do become toasty it seems SO8 sans pad won't be >better.How much power do you need to dump? -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●January 20, 20182018-01-20
On 2018-01-20 16:16, John Larkin wrote:> On Fri, 19 Jan 2018 15:57:08 -0800, Joerg <news@analogconsultants.com> > wrote: > >> On 2018-01-19 15:45, John Larkin wrote:[...]>>> I've dissipated 3 watts from a SOT89 soldered to a copper pour. >>> >>> https://www.dropbox.com/s/rkg3jkzvqutl822/DSC01850.JPG?raw=1 >>> >>> https://www.dropbox.com/s/iy5gyxjvgi14sf1/DSC01857.JPG?raw=1 >>> >>> Thermal vias could make this better. >>> >> >> Good words of wisdom. I'll stay with SOT89 then. That is what I used >> before and while they do become toasty it seems SO8 sans pad won't be >> better. > > How much power do you need to dump? >Not sure yet but probably 500mW or a little more per device. Things shouldn't get too hot to touch though. It is also a sort of hi-rel application where the product lifetime should be several decades. -- Regards, Joerg http://www.analogconsultants.com/
