TPS51206: Recommended Operating Die Temperature

Team-

Could I get some help with this question?

Thanks,

Alec

John-

Thanks for your response. While I understand there is probably little characterization done (and it's not your device!), do you think that there will be any loss of functionality or performance as the device junction temperature approaches the Abs max of 125C? Is there any general margin that you would recommend in terms of this junction temperature from the Abs Max? It would be nice to give the customer at least a general guideline of how hot the junction can get before they should be concerned or re-evaluating the design.

Thanks,
Alec

Typically the allowed power dissipation decreases as Ta approaches the maximum junction temperature. So at Ta = 125 C, allowable power dissipation = 0 W. Most of the datasheet parameters are tested in "open loop" condition, so that Tj is very close to Ta during testing as only negligible power is dissipated. Some parameters may be out of specification at Tj above 85 C. Let me see if I can get someone from the product line to comment directly.

Hi Alec,

What's the ambient temp and Vin/Vout/Iout in your application?

Thanks
Qian

Qian,

I’m working with Alec Forbes on this Raytheon application for the TPS51206, which is in a complex thermal environment.  He is using PCB tools in a comprehensive thermal simulation.

This is a DDR3 application with the following parameters:

               VDD = 5.0V (+/-5%)

               VDDQSNS = 1.5V (+/-5%)

               VLDOIN = VDDQSNS

               I (VTT) = 0.5A  (only ¼ of the 2A capacity)

               VTT = ½ VDDQSNS

               VTTREF = ½ VDDQSNS 

               VTTSNS = VTT 

The “ambient” temperature isn’t easy to directly determine because the ambient air temp is significantly different from the ambient board temperature.  His simulation is showing a junction temperature of about 102 deg C, well under our 125C max Tj spec.  However, depending on how you measure ambient temp he may not be strictly meeting our 85C max ambient spec. 

I have encountered this scenario a few times before, particularly for devices that have a minimal temp rise, where the customer application technically violates our 85C max ambient temp but where they are fully compliant with our 125C max junction temp. 

Is there a general statement we could share with the customer, indicating that our device will meet its datasheet performance parameters as long as they ensure that the junction temp is maintained below 125C?

On another subject, I believe there is an error in our TPS51206 datasheet.  In table 6.1 (ABS Max Ratings), we show a max TJ of 125C which looks fine.  However, this table also shows a max “Operating free-air temperature Ta” of 150C.  I don’t think this can be right.  Do you agree?

David

---------------------------------
David Hildebrand
Analog Field Applications
South Region
Texas Instruments, Inc.
Office:  214-479-0917
Cell:       972-841-6499
david.hildebrand@ti.com
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HI David,

I checked the test data. At 125c junction temperature, the VDD supply current and VLDOIN supply current at some conditions are out of SPEC on datasheet. Other parameters are still in the SPEC but might with small margin.

If the junction temperature is 102c in customer's application, I think the risk is low if VDD supply current and VLDOIN supply current are not the concern to customer.

Thanks

Qian