AM3352: POH and reliability questions

Brian Bell (TSR Rochester, NY) said:

1. What happens after the POH rating?  What degrades or fails?

Please see the following application note:

Calculating Useful Lifetimes of Embedded Processors
http://www.ti.com/lit/sprabx4

It discusses this topic in-depth.  Chapter 3 in particular discusses wear-out mechanisms.

Brian Bell (TSR Rochester, NY) said:

2. What is the Lifecycle vs. Junction Temperature for AM3352?   Please provide characterization tables or curves.

In your particular case (AM3352BZCZA60), the max operating speed of the MPU is 600 MHz, aka OPP100.  That means the data points of interest are:

1. -40 to 105C -> 100k PoH
2. -40 to 125C -> 35k PoH

Keep in mind that high temp is what accelerates aging in these devices.  In other words, the two data points above are telling us:

1. Operating the device at 105C at all times we can expect 100k PoH.
2. Operating the device at 125C at all times we can expect 35k PoH.

So the important thing to note here is that if you're not operating at 125C all the time then you can expect to have more than 35k PoH.

Section 4.2 of the app note talks about de-rating.  It shows an acceleration factor of 0.2 for operating at 125C.  So for example, let's say we expect to operate 1k hours at 125C.  We take that 1k hours and divide by our acceleration factor of 0.2 which means that 1k hours at 125C is equivalent to 5k hours at 105C in terms of aging.  Since we are expecting 100k PoH at 105C, that means we can run 95k hours at 105C plus 1k hours at 125C.  

Similarly, you could run for 10k hours at 125C plus 50k hours at 105C.

Brian Bell (TSR Rochester, NY) said:

3. What is the lowest operating frequency the A60 can run down to?  Customer wants to use A60 (lower cost than T60) and would lower the operating frequency as the junction temperature rises to stay below the 105C Tjmax.  

There's not a minimum frequency requirement, though in practice most customers use our defined OPP's, e.g. 300 MHz or 600 MHz.

Brian Bell (TSR Rochester, NY) said:

4. What additional power management techniques can be deployed to lower the Tj – shut down peripherals, etc?

Dropping to 300 MHz allows you to correspondingly drop VDD_MPU to 0.95V, which gives you a major power reduction compared to the 600 MHz operation at 1.1V.  That's going to be your biggest power knob with respect to this device. I expect that should be sufficient.

Brian Bell (TSR Rochester, NY) said:

5. Customer did not plan to use a heat sink, but if that would help, what heat sinks does TI recommend?  Are there any heat sinks that are known to be compatible with the ZCZ package?

I don't think that should be necessary if you take advantage of DVFS to utilize both OPP50 and OPP100.

Brian Bell (TSR Rochester, NY) said:

6. Is AM335x used in automotive applications and how do those customers deal with these reliability questions?

The following note is from page 4 of the app note:

For automotive grade products that are specified above 105°C TJ, their reliability mission
profile is targeted for an AEC-Q100 mission profile of 15 years on with ~12% duty cycle. The
total time at Tmax is usually a small subset of their total power on time.

15 years at 12% duty cycle is only about 16k PoH.

let me add that today we have in production AM3352BZCZT60 that is qualified at 125C.