[SI-LIST] Re: Power dissipation- Ambient temperature
- From: Wyland <dcwyland@xxxxxxxxxxxxx>
- To: prasannar@xxxxxxxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Mon, 16 Feb 2004 10:39:19 -0800
Temperature will increase with time until it stabilizes at a temperature
where heat flow from the
chips to their packages equals heat flow from thepackages to ambient,
either by convection or
by using a fan.
Power dissipation comes from several sources: AC power charging and
discharging
capacitance, and AC power from the crossover transient when both N and P
channels are
conducting as the input to a gate or inverter goes through the
transition region, and leakage.
AC power from capacitance should remain a constant function of frequency
and voltage.
The energy per transition is 1/2 CV^2. The AC power from the crossover
transient
should decrease with temperature because the resistivity of silicon
increases with temperature.
This means that the current spike will be reduced as power goes up.
Leakage used to be vanishingly small until we hit 0.13 micron. Now,
leakage can be
a significant percentage of the total current depending on the design.
Unfortunately,
leakage increases rapidly - exponentially - with temperature.
Net result is that the power should decrease slightly or at least remain
constant
with respect to temperature. If it increases with temperature, the chip
has the
potential of thermal runaway, where increasing power leads to increasing
temperature, etc. until the chip is fried. This must be prevented by
design.
Dave
Prasanna R - CTD, Chennai. wrote:
>Hello,
> Power dissipation of CMOS, Bi-CMOS, TTL devices depend on ambient
>temperature.
>Power dissipation of these devices will increase the temperature around
>these devices.
>So, power dissipation increases with time as the temperature around it is
>increasing.
>But power dissipation is calculated independent of time. Please explain?
>
>thank you,
>Prasanna R
>------------------------------------------------------------------
>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.org
>
>List archives are viewable at:
> //www.freelists.org/archives/si-list
>or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
>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.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
