Re: [IBIS] Determining correct Junction temperature for IBIS models

Hi, Bonnie,

A "rule of thumb" temperature rise is 25C for a
chip. Personally, I like to use the lowest
operating temperature (-40C) as-is to capture the
coldest temperature at which the I/O might be
asked to operate.

If a more detailed calculation is needed, here are
some things to consider:
* Are those power numbers for an entire chip,
core, I/O ring, or a single I/O?
* What are the thermal resistance and time
constant for I/O junction to package?
* How many I/O can toggle at the same time?
* What is the current drawn by the I/Os during
switching?
=> peak operating power for the I/O ring + core at
5.5V?
=> worst-case temperature rise at a junction.

Other places to look include the IBIS Cookbook and
Istvan Novak's site.
http://www.eda.org/ibis/cookbook/cookbook-v4.pdf

Best regards,
Lynne

"IBIS training when you need it, where you need it."

Dr. Lynne Green
Green Streak Programs
http://www.greenstreakprograms.com
425-788-0412
lgreen22@mindspring.com

On 6/26/2011 2:22 PM, Baker, Bonnie wrote:
>
> IBIS experts,
>
> I am in the midst of creating numerous IBIS
> models for a wide variety of products. The issue
> that has come up is the selection of the proper
> junction temperature values for my 3 corners.
>
> Given that the specified temperature for a
> device is -40 C to 85C.
>
> Corner supplies are 4.5V, 5V, and 5.5V.
>
> The package theta-ja 100 C/W.
>
> The nominal *room* temperature *quiescent* power
> dissipation at 5V power supply voltage is 50 mW.
> theta-ja * 50mW = 5C
>
> The nominal *room* temperature *operating* power
> dissipation at 5V power supply voltage is 100
> mW. theta-ja * 100mW = 10C
>
> The nominal *cold* power *quiescent* dissipation
> (@ -40C, 5V supply) is 40mW. theta-ja * 40mW = 4C
>
> The nominal *cold* power *operating* dissipation
> (@ -40C, 5V supply) is 80mW. theta-ja * 80mW = 8C
>
> The nominal *hot* power *quiescent* dissipation
> (@ 85C, 5V supply) is 60mW. theta-ja * 60mW = 6C
>
> The nominal *hot* power *operating* dissipation
> (@ 85C, 5V supply) is 120mW. theta-ja * 120mW = 12C
>
> Which option is correct?
>
> Option 1: Create IBIS model with
>
> *-40C, 25C, and 85C* temperatures
>
> Option 2: Calculate nominal quiescent room
> temperature power dissipation and multiply that
> times the package theta-ja. Add this delta
> temperature to all three temperatures. In this
> case the IBIS temperatures are
>
> *-35C, 30C, and 90C*.
>
> Option 3: Calculate nominal quiescent room
> temperature power dissipation and multiply that
> times the package theta-ja. Add this delta
> temperature to the two higher temperatures. In
> this case the IBIS temperatures are
>
> *-40C, 30C, and 90C*.
>
> Option 4: Calculate the quiescent power
> dissipation at all temperatures and multiply
> that times theta-ja. The IBIS temperatures in
> this case would be
>
> *-36C, 30C, and 91C*.
>
> Option 5: Apply the mathematics of quiescent
> power and theta-ja to the two higher
> temperatures. In this case the IBIS temperatures
> are
>
> *-40C, 30C, and 91C*.
>
> Option 7: Apply Option 2 to operating power
> dissipation conditions. In this case the IBIS
> temperatures are
>
> *-30C, 35C, and 95C*.
>
> Option 8: Apply Option 3 to operating power
> dissipation conditions. In this case the IBIS
> temperatures are
>
> *-40C, 35C, and 95C*.
>
> Option 9: Apply Option 4 to operating power
> dissipation conditions. In this case the IBIS
> temperatures are
>
> *-32C, 35C, and 97C*.
>
> Option 10: Apply Option 5 to operating power
> dissipation conditions. In this case the IBIS
> temperatures are
>
> *-40C, 35C, and 97C*.
>
> Option 11: Add 15 deg C to -40C, 25C, and 85C or
> create IBIS model with
>
> *-25C, 40C, and 100C*.
>
> Option 12: Add 15 deg C to 25C and 85C or create
> IBIS model with
>
> *-40C, 40C, and 100C*.
>
> Bonnie
>
>
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