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? -- Regards, Joerg http://www.analogconsultants.com/
SO8 versus SOT89 junction to ambient?
Started by ●January 19, 2018
Reply by ●January 19, 20182018-01-19
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.pdfLooks like they heat-sunk the SO8 but maybe didn't the SOT89.> >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. 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. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 19, 20182018-01-19
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 > >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?There's probably a die-size difference between positive and negative regulators... since good PNP's aren't native to a P-substrate process. Don't ask me to calculate... I've reached my energy-expenditure limit for the day... time to continue with our viewing of the five-seasons of "Boardwalk" ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | It's what you learn, after you know it all, that counts.
Reply by ●January 19, 20182018-01-19
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. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●January 19, 20182018-01-19
Den lørdag den 20. januar 2018 kl. 00.47.46 UTC+1 skrev Jim Thompson:> 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 > > > >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? > > There's probably a die-size difference between positive and negative > regulators... since good PNP's aren't native to a P-substrate process.both the negative and positive use NPN output
Reply by ●January 19, 20182018-01-19
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 datasheet
Reply by ●January 19, 20182018-01-19
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 datasheetSomeone could maybe make a business out of proofing data sheets. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 19, 20182018-01-19
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 datasheet > > 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
Reply by ●January 19, 20182018-01-19
On Fri, 19 Jan 2018 16:10:51 -0800 (PST), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>Den l�rdag den 20. januar 2018 kl. 00.47.46 UTC+1 skrev Jim Thompson: >> 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 >> > >> >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? >> >> There's probably a die-size difference between positive and negative >> regulators... since good PNP's aren't native to a P-substrate process. > >both the negative and positive use NPN outputSziklai-style. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | It's what you learn, after you know it all, that counts.
Reply by ●January 20, 20182018-01-20
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 datasheet >> >> 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 :DBut the errors are rarely fixed, after years and decades. -- John Larkin Highland Technology, Inc lunatic fringe electronics
