[SI-LIST] Re: Power dissipation low or high
- From: Mike Brown <bmgman@xxxxxxxxxx>
- To: "N. Paul Taddonio" <paul.taddonio@xxxxxxxxxxxxxx>
- Date: Sat, 05 Feb 2011 01:24:13 -0600
Paul,
You have pretty well nailed it. The power specs in the IC data sheet are
*package* specifications. The clue in the case of Fairchild is the fact
that there are two, package-dependent, power specs for the device, as a
function of package. Fairchild ap note AN-1100 discusses thermal
management. ST specs it explicitly as a package limit.
As to the device dissipation, the quiescent power is about nil, and the
output transistor dissipation is at most a few milliwatts (Vol * Iol,
for instance), and there are only 4 outputs. As to the "power switching
capacitance" (F*C*V^2) dissipation, Geetha will have to analyze that for
his external loads. Internally, FCV^2 at 10 MHz and 5 volts should be
nearly negligible (compared to 200 mW package specs) since there are
only 4 SSI gates in the package.
Finally, not all package thermal specs are created equally. They are
dependent on board topology (how much copper is there in the board to
conduct heat away, for instance), die size, and air flow. You can't know
whether the two package power specs are equivalent without doing a whole
lot of work, but both appear to be well above the device dissipation,
unless it is switching fast, or is heavily loaded.
All else being equal, I would not hesitate to consider the two parts
equivalent unless the application is really pushing the envelope with
respect to power dissipation. But you have to analyze it to know.
Regards
Mike
- - - - -
N. Paul Taddonio wrote:
>Geetha,
>
>The fairchild 500 mW. max power spec is saying you should not cause the part
>to dissipate any more than that.
>
>Because the package can't remove the heat fast enough, worst case.
>
>Your application of the part will determine its actual power, for example,
>the power dissipated is a function of
>the average toggle frequency of each gate, per its "power dissipation
>capacitance" specification: 24 pF
>
>You should at least estimate your actual power, because you should not use
>the part near its absolute maximum.
>
>The St micro part is a decade newer, has a 200 mW max and does not spec its
>"power dissipation capacitance",
>likely its too low to matter. It may dissipate less heat and so be OK in a
>lower capacity package.
>
>Its possible you won't be approaching either parts max spec and so it
>doesn't matter.
>
>Sincerely,
>Paul Taddonio
>
>
>
>----- Original Message -----
>From: "Geetha Balasubramanian" <geethukarrthik@xxxxxxxxx>
>To: <si-list@xxxxxxxxxxxxx>; "Andrew Ingraham" <a.ingraham@xxxxxxxx>
>Sent: Friday, February 04, 2011 12:50 AM
>Subject: [SI-LIST] Re: Power dissipation low or high
>
>
>
>
>>Dear Andy &Â Steve,
>>Â
>>Thanks for your reply to my query.
>>Â
>>I was also having the same opinion and got doubly convinced after seeing
>>your replies. But after hearing from the ST Micro tech support team I am
>>confused.
>>For the Fairchild part â?oCD4093BCMâ?? the absolute maximum power
>>dissipation is 500 mw as per the datasheet.
>>For the ST Micro part â?oHCF4093M013TRâ?? the absolute maximum power
>>dissipation is 200 mw as per the datasheet.
>>ST Micro tech support team explained me that Fairchild parts are better in
>>this segment than ST Micro parts from the power dissipation perspective.
>>Our design engineers  are not ready to accept ST Micro part as an
>>alternate to Fairchild part stating â?oST Micro part is poor in power
>>perspectiveâ??.
>>Is there any way to conclude without doing a practical testing?
>>Â
>>Thanking in advance
>>Â
>>Geetha
>>--- On Mon, 31/1/11, Andrew Ingraham <a.ingraham@xxxxxxxx> wrote:
>>
>>
>>From: Andrew Ingraham <a.ingraham@xxxxxxxx>
>>Subject: [SI-LIST] Re: Power dissipation low or high
>>To: si-list@xxxxxxxxxxxxx
>>Date: Monday, 31 January, 2011, 10:02 PM
>>
>>
>>
>>
>>>Which one is good from power perspective? Higher power
>>>dissipation means the part is capable of withstanding more
>>>dissipation so it is better? Is this understanding correct?
>>>
>>>
>>For an IC, power dissipation usually means how much power the IC
>>actually uses, not how much the package is capable of withstanding.
>>Thus, lower is better "from a power perspective."
>>
>>Zero would be even better.
>>
>>Andy
>>------------------------------------------------------------------
>>To unsubscribe from si-list:
>>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>>
>>or to administer your membership from a web page, go to:
>>//www.freelists.org/webpage/si-list
>>
>>For help:
>>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>>
>>
>>List technical documents are available at:
>>Â Â Â Â Â Â Â Â http://www.si-list.net
>>
>>List archives are viewable at:Â Â Â Â
>>Â Â Â Â Â Â //www.freelists.org/archives/si-list
>>
>>Old (prior to June 6, 2001) list archives are viewable at:
>>Â Â Â Â Â Â http://www.qsl.net/wb6tpu
>>Â
>>
>>
>>
>>
>>------------------------------------------------------------------
>>To unsubscribe from si-list:
>>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>>
>>or to administer your membership from a web page, go to:
>>//www.freelists.org/webpage/si-list
>>
>>For help:
>>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>>
>>
>>List technical documents are available at:
>> http://www.si-list.net
>>
>>List archives are viewable at:
>>//www.freelists.org/archives/si-list
>>
>>Old (prior to June 6, 2001) list archives are viewable at:
>> http://www.qsl.net/wb6tpu
>>
>>
>>
>>
>>
>>
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>or to administer your membership from a web page, go to:
>//www.freelists.org/webpage/si-list
>
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
>List technical documents are available at:
> http://www.si-list.net
>
>List archives are viewable at:
> //www.freelists.org/archives/si-list
>
>Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
>
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
