VGEN2 is not as per PMIC programming

[riteshpatel]

Hi,

We are working on iMX8M based custom board & powered processor using MC34PF4210A1ES PMIC. 

Observed that VGEN2 voltage is 1.4V, which is not as per PMIC programming. It should be 0.9V.

Tried to debug by removing one series resistor between PMIC & processor PHY power rails. See R165 in attached PMIC schematic. After removing R165, we are getting 0.9V on VGEN2. But on the other end of the resistor, we are getting 1.4V.

Please let me know what could be the reason for this.

Find attached schematic of PMIC & CPU power for your reference.

Thanks.

[riteshpatel]

We have assembled another board. On that 2nd board, VGEN2 voltage is 0.9V, as expected.

During power up for around 1Sec , VGEN2 rail goes upto 1.4V & settle down to 0.9V & remains stable then after. 

On first board, I am still getting 1.4V, though my USB, HDMI & mPCIe peripherals are working on that board.

What is the absolute max operating voltage on USB, PCIe & HDMI CPU power rails:  VPTX, VP, DVDD, AVDDCORE rails?

Is it Okay to operate the board with 1.4V on above power rails? 

[art]

1.4V is out of specification for the power rails you've specified. The maximum specified voltage for these rails is 1.0V.

Best Regards,
Artur

[art]

As far as I can see from the schematics you've provided, the power part of your design is very similar to the one of the i.MX8M EVK board. On the EVK board, there is the stable 0.9V voltage on the VDD_PHY_0V9 power rail. So, the possible cause of the 1.4V voltage injection to this power rail from the processor side is some voltage back leakage condition on one of the interfaces (USB, PCIe, MIPI, HDMI) this power rail supplies. So, please check it first. Please also check the voltages on the VDD_PHY_1V8 and VDD_PHY_3V3 power rails.

Another possible cause of the issue is some PCB level design problem, e.g. shorted traces etc. Please check it as well.

Have a great day,
Artur

-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
-------------------------------------------------------------------------------

[riteshpatel]

Hi,

After removing resistor R165, Getting 0.9V at PMIC output & 1.4V on Processor PHY power rails.

Can any one check & update what could be the possibilities for 1.4V from processor side?

Thanks.

[先生孟]

Hi Patel:

   I'm working the same PMIC and CPU, I have the same problem, the PMIC VGEN2 out the voltage is 1.35V instead of 0.9V, I have checked all voltages of this PMIC , all voltages are correct except of this VDD_PHY_0V9, I don't know what's problem