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

From my perspective the problem here is having to choose one set of
temperatures. If it was a SPICE model users could dial in whatever
temperatures and voltages the part will actually see in the given
application. But vendors are the ones to choose those values when they make
IBIS models. Since they often put min and max at the extremes of voltage and
temperature for the part, users are forced to leave margin on the table when
the parts are not used at those extremes.

My preference would be multiple IBIS [Component] sections with different
ranges, or [Model Selector]. For example, 5% voltage tolerance would be much
closer to reality, yet still conservative for us. Some people would like a 0
degree model even if the part goes down to -40, etc. I will not ask for both
91 and 100 degrees though.

Addressing Bonnie's question a little more directly, the lowest temperature
should be at turn on, no power dissipation modeled. Again, two low
temperatures would be good if the part goes below zero. I have no advice
about typical, we never use it. For max temperature I would certainly
include operating temperature at a high ambient, but also at a lower ambient
too.

Mike
On Jun 26, 2011 5:24 PM, "Baker, Bonnie" <bonnie@ti.com> 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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>

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