On Sunday, January 21, 2018 at 10:33:30 AM UTC-5, Joerg wrote:
> On 2018-01-20 17:07, dagmargoodboat@yahoo.com wrote:
> > On Saturday, January 20, 2018 at 2:55:52 PM UTC-5, Joerg wrote:
> >> 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/
> >
> > Look at the difference between the
> > a) SO-8's junction-to-case and (20°C/W)
> > b) junction-to-ambient-with-6cm^2-heatsink. (55°C/W)
> >
> > This amounts to 35°C/W for the heatsink-to-ambient portion.
> >
> > Apply that to the SOT89, 15°C/W + 35°C/W = 50°C/W to ambient, with the
> > same copper pour.
> >
>
> That's what we don't know and what a datasheet should specify.
>
>
> > (I'm assuming they're measuring to the leads rather than the actual
> > epoxy case, otherwise their lower junction-to-case for the SOT89
> > wouldn't make sense--it's thicker than an SO-8.)
> >
>
> Still, that's assumptions and I can't design on assumptions but John has
> hard data so that's good.
1. John doesn't have data on your specific SO-8, but the manufacturer has
provided specifications for it, in actual application, no assumptions
required.
But it's moot--both sources indicate that the SOT89 wins.
2. There are many application notes for estimating the thermal resistance
of a 6cm^2 copper pour--that's not top secret.
This reference reports 40°C/W for an SOT223 with a topside 1 inch^2 2oz pour:
http://www.onsemi.com/pub/Collateral/AN-1028.pdf.pdf
3. There are outstanding SO-8 packages built on giant copper slab thermal
pads. I've used some. But your example here isn't of that construction.
Cheers,
James Arthur
Reply by Joerg●January 21, 20182018-01-21
On 2018-01-21 09:44, John Larkin wrote:
> On Sat, 20 Jan 2018 16:20:31 -0800, Joerg <news@analogconsultants.com>
> wrote:
>
>> 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.
>
> Half a watt should be easy from a SOT89. A little topside copper patch
> maybe. If you don't have much room, via down to a copper pour on the
> bottom and/or an inner layer. An isolated inner layer pour will spread
> heat and dump heat into adjacent planes.
>
No space at all, this board will look like the inside of a Tokyo subway
during rush hour. After the pushers have squeezed the people in. So
it'll have to be a few vias without thermal reliefs to a copper plane
inside the board.
--
Regards, Joerg
http://www.analogconsultants.com/
Reply by John Larkin●January 21, 20182018-01-21
On Sun, 21 Jan 2018 07:33:24 -0800, Joerg <news@analogconsultants.com>
wrote:
>On 2018-01-20 17:07, dagmargoodboat@yahoo.com wrote:
>> On Saturday, January 20, 2018 at 2:55:52 PM UTC-5, Joerg wrote:
>>> 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/
>>
>> Look at the difference between the
>> a) SO-8's junction-to-case and (20�C/W)
>> b) junction-to-ambient-with-6cm^2-heatsink. (55�C/W)
>>
>> This amounts to 35�C/W for the heatsink-to-ambient portion.
>>
>> Apply that to the SOT89, 15�C/W + 35�C/W = 50�C/W to ambient, with the
>> same copper pour.
>>
>
>That's what we don't know and what a datasheet should specify.
Data sheet thermals are generally not to be trusted. When in doubt,
experiment.
An 0603 resistor will safely dump half a watt, if you do it right.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
Reply by John Larkin●January 21, 20182018-01-21
On Sat, 20 Jan 2018 16:20:31 -0800, Joerg <news@analogconsultants.com>
wrote:
>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.
Half a watt should be easy from a SOT89. A little topside copper patch
maybe. If you don't have much room, via down to a copper pour on the
bottom and/or an inner layer. An isolated inner layer pour will spread
heat and dump heat into adjacent planes.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
Reply by Joerg●January 21, 20182018-01-21
On 2018-01-20 17:07, dagmargoodboat@yahoo.com wrote:
> On Saturday, January 20, 2018 at 2:55:52 PM UTC-5, Joerg wrote:
>> 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/
>
> Look at the difference between the
> a) SO-8's junction-to-case and (20°C/W)
> b) junction-to-ambient-with-6cm^2-heatsink. (55°C/W)
>
> This amounts to 35°C/W for the heatsink-to-ambient portion.
>
> Apply that to the SOT89, 15°C/W + 35°C/W = 50°C/W to ambient, with the
> same copper pour.
>
That's what we don't know and what a datasheet should specify.
> (I'm assuming they're measuring to the leads rather than the actual
> epoxy case, otherwise their lower junction-to-case for the SOT89
> wouldn't make sense--it's thicker than an SO-8.)
>
Still, that's assumptions and I can't design on assumptions but John has
hard data so that's good.
--
Regards, Joerg
http://www.analogconsultants.com/
Reply by ●January 20, 20182018-01-20
On Saturday, January 20, 2018 at 2:55:52 PM UTC-5, Joerg wrote:
> 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/
Look at the difference between the
a) SO-8's junction-to-case and (20°C/W)
b) junction-to-ambient-with-6cm^2-heatsink. (55°C/W)
This amounts to 35°C/W for the heatsink-to-ambient portion.
Apply that to the SOT89, 15°C/W + 35°C/W = 50°C/W to ambient, with the
same copper pour.
(I'm assuming they're measuring to the leads rather than the actual
epoxy case, otherwise their lower junction-to-case for the SOT89
wouldn't make sense--it's thicker than an SO-8.)
Cheers,
James Arthur
Reply by Joerg●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:
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/
Reply by John Larkin●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 Joerg●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.
>
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