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

Bonnie

I think you should look at operating temperatures and ignore the quiescent
dissipation. The part does not have SI characteristics if no real work is
being done. Does your operating dissipation include the I/O drivers' power
dissipation or just the chip. You really need to look at total dissipation.

Common practice is to use the actual die temperature at the conditions of
operation.

Tom Dagostino

Teraspeed Labs

9999 SW Wilshire St.

Suite 102

Portland, OR 97225

USA

971-279-5325 Office

971-279-5326 FAX

503-430-1065 Cell

tom@teraspeed.com

www.teraspeed.com <http://www.teraspeed.com/>

Teraspeed Consulting Group LLC

121 North River Drive

Narragansett, RI 02882

401-284-1827

From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Baker,
Bonnie
Sent: Sunday, June 26, 2011 2:23 PM
To: ibis@server.eda-stds.org
Subject: [IBIS] Determining correct Junction temperature for IBIS models

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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