working ambient range of AM335x@800Mhz?

The answer to your question depends on many variables like PCB size, plane layers, other power sources on the same PCB, air flow, etc.

A new revision of the data sheet will be published next week and it references a new thermal application note that will also be published next week.  This document should help answer your thermal questions.

Regards,
Paul

Paul,

Could you please review if my computation below is correct.

I want to know what ambient range AM335x can have.

I suppose that 2W is consumed at room temperature(25degree). At that condition, let’s assume that the surface temperature of AM335x is 45degree

 From datasheet, we can find following data.

JtoC: Junction-to-case                   = 10.2

JtoB: Junction-to-board                 =12.1

JtoA: Junction-to-free air             =24.2

JtoT: junction to package top      =0.3

1)junction temperature.( I used JtoT, but I don’t know well what JtoC or JtoT is…)

Tj = Tp + JtoT*Power = 45C + JtoT*2W = 45 + 0.3*2 = 45.6C

2)J-to-A computation

                Tj=Ta + J-to-A*W  => 45.6 = 25 + J-to-A*2  => J-to-A = (45.6-25)/2=10.3

Then, we can compute Tj for specific Ta. If Ta=80degree, Tj will be greater than 100degree.

                Tj=80+10.3*2W = 100.6degree

if we use industrial grage(max Tj=90), AM335x will stand up to about 69degree.

                Tj=Ta + J-to-A*W  => 90 = Ta+10.3*2W. Ta=90-20.6 = 69.4degree

Thanks Best Regards,

Devin

Devin,

The thermal application note can be found here: http://processors.wiki.ti.com/index.php/AM335x_Thermal_Considerations

Your computations are correct, but there are some inaccuracies when using Theta-JA because it does not account for several factors unique to the test system.  Regardless, I have collect some experimental data on our EVM that correlates with your 69.4C estimate.  This graph illustrates the thermal performance of the GP EVM running the Dhrystone benchmark at different frequencies and ambient temperatures.  For 1GHz Dhrystone, the AM335x could operate in a ~64C ambient environment without exceeding a 90C junction temperature.  For 800MHz Dhrystone, this ambient temperature was ~67C.  Running an OS Idle application (minimal active power) at 800MHz, the maximum operating ambient temperature was ~73C.

As Paul mentioned, thermal performance is very system-dependent, so it is difficult to specify a maximum ambient temperature for your (or any) system.  For commercial/industrial temperature range devices, it is unlikely that you will be able to run 3D graphics and Ethernet at 800MHz in an 85C environment, without incorporating a significant amount of power management techniques.  This is because you are only providing a 5C degree margin between the ambient temperature and the 90C maximum operating junction temperature.  It will be more reasonable to use an extended temperature range device, which has max junction temp of 105C.

What is your end application?  And what is the intended environment?

The "graph" link above seems to be broken: http://processors.wiki.ti.com/index.php/File:JvA_Dhry_dis.png

Internet marketing team is working to fix the link.

Sorry...