AM4376: Main oscillator issue

Tony Spagnolia1

Part Number: AM4376
Other Parts Discussed in Thread: TPS65218D0,

I have a design which I know works (29 of 30 processors are coming up correctly from power up between the boards I am testing), so I am looking for general troubleshooting tips on what to look for in this scenario.

On intiial power up, the PMIC is supplying the rails in sequence as desired MPU, DDR, CORE, IO and the PGOOD signal is coming up as high after the sequence as well. However, the CPU does not output the oscillator and the CPU is holding the NRESET signal low. I have replaced the oscillator with a known good oscillator, so that is not the issue.

From what I could find in the technical reference manual, it looks like DeepSleep or RTC-Only mode shuts off the oscillator. Could the CPU somehow get confused and think its in this mode? Or is there another cause of this situation?

Thanks,

Tony

over 5 years ago

0 Brian Berner over 5 years ago

TI__Mastermind 30310 points

Tony,

I am going to re-assign this question to the Sitara AM437x team and see if they agree with your assessment. If not, we can go back and look at the TPS65218D0 PMIC in more detail.

0 Brian Berner over 5 years ago in reply to Brian Berner

TI__Mastermind 30310 points

Tony,

Sorry for the confusion, this is already assigned to the Sitara Processor team. It came up on my feed and said "TPS65218D0" so I assumed it got routed to the PMIC team accidentally.

0 Biser Gatchev-XID over 5 years ago

TI__Guru**** 393215 points

Tony Spagnolia1 said:
CPU does not output the oscillator

Is this a crystal or an external oscillator? What frequency?

Tony Spagnolia1 said:
CPU is holding the NRESET signal low

Do you mean nRESETIN_OUT? Please clarify.

0 Tony Spagnolia1 over 5 years ago in reply to Biser Gatchev-XID

Prodigy 190 points

Hi Biser,

The oscillator is a 25 MHz ABM3-25.000MHZ-D2Y-T for OSC0.

And yes, the NRESETIN_OUT signal is being held low.

Thanks,

Tony

0 Biser Gatchev-XID over 5 years ago in reply to Tony Spagnolia1

TI__Guru**** 393215 points

As far as I see, this is a 25MHz crystal, not an oscillator. Since this is only 1 board out of 30 I would suggest you look for some manufacturing issue, e.g. defect PCB, bad soldering, shorts, etc.

0 Tony Spagnolia1 over 5 years ago in reply to Biser Gatchev-XID

Prodigy 190 points

My apologies on the confusion on crystal vs oscillator.

And I agree, I believe it is a manufacturing defect which I haven't been able to track down. I don't measure shorts, or see anything from an inspection. What I was hoping for was what can cause the AM4376 to disable the crystal which will help me in troubleshooting.

Thanks,

Tony

0 Biser Gatchev-XID over 5 years ago in reply to Tony Spagnolia1

TI__Guru**** 393215 points

This is not a case of the processor disabling the crystal, rather the processor itself does not start. One thing that you should verify is that you do not have any external voltages present on processor I/O pins before the device is powered up. This can prevent the processor from starting up properly and even damage it.

0 Tony Spagnolia1 over 5 years ago in reply to Biser Gatchev-XID

Prodigy 190 points

I agree the CPU is not starting. As I had mentioned in the post, the power sequencing is correct and identical to the other 29 CPUs that are functioning correctly. Something else is happening to cause the CPU to not start. I am looking for a list of what could cause the CPU not to start besides the sequencing.

Thanks,

Tony

0 Biser Gatchev-XID over 5 years ago in reply to Tony Spagnolia1

TI__Guru**** 393215 points

Could be a bad ball soldering, or a short under the processor. You could try resoldering the processor. I suggest you also check passive components, they may crack sometimes. There is really no way to make such a list as you request, designs differ too much.

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AM4376: Main oscillator issue