i.MX8MN :- Power up issues

[milav_soni]

Hello Team,

This is Milav Soni From Teq Diligent.

I have made a custom board which have "MIMX8MN1CVTIZAA" Processor and we have used "BD71847AMWV-E2" PMIC IC to give all power to MPU.

We have taken reference of EVK Schematic and made a custom H/W.

Problem :- Processor Does not power up, It does not give "PMIC_ON_REQ" High signal to PMIC.

Connection :- 

1) PMIC_ON_REQ -> Directly Connected to PMIC with 0E.

2) PMIC_STBY_REQ -> Directly Connected to PMIC with 0E.

3) WDOG_B -> GPIO1_IO02/Wdog_b connected to PMIC with 0E and 100k pull up with "NVCC_1V8" Power supply at PMIC side.

4) PWRON_B -> Connected to NVCC_SNVS_1V8 with 100K Pull Up Resistor.

Currently, We Got Following outputs in Following Condition.

      Condition :- PMIC_ON_REQ is disconnected from PMIC.

      Output :- We got CLK_32K_OUT, RTC_RESET_B, LDO1 and LDO2 Supply, PMIC_ON_REQ High on Processor side

But When PMIC_ON_REQ is Connected to PMIC than We does not got the PMIC outputs.

Can you please help me to sort out this issues?

If you have any need please tell me.

Thank You

[milav_soni · Accepted solution]

Hello @weidong_sun 

Thank You for your support.

We got the root of problem and Find Solution.

The problem is one Connection between PMIC and MPU open.

Now My board is power up and Got All Voltages.

Thank You

[weidong_sun]

Hi, milav_soni,

>>WDOG pin is low.

When WDOG sends out a reset signal, it will output LOW level, and then will be pulled down HIGH level by the pull-up resistor. So, first disconnect WDOG net between CPU and PMIC.

1. Check if the PMIC can work.

2. Measure whether the WDOG on the CPU side is HIGH or LOW.

>>What is reason for PMIC_ON_REQ become Low? 

You have verified that the output from the CPU side is HIGH, but when connected to the PMIC, it will become LOW, indicating that the problem is on the PMIC side. So you need to check whether there is a problem with the SMT of the PMIC.

Hope above advice is helpful to you.

Have a nice day!

B.R,

Weidong

[milav_soni]

Hello @weidong_sun 

Thank You For your response.

We have measured WDOG_B Voltage in MPU Side when it is disconnected from PMIC, It is 0V and pmic is not generating output other than LDO1 and LDO2.

And we measured LD02 Voltage is 0.9v Instead of 0.8V, can this affect on pmic_on_req signal or any other interface/Blocks of MPU?

When pmic_on_req is connect than and than the pmic buck and ldo voltage are not generate and it gives 5 pulses at 300ms interval and on for 20ms.

Please find attached images. second image is Showing waveform of PMIC_5V (Yellow Channel) vs PMIC_ON_REQ(Blue Channel) and first image is Showing waveform of PMIC_5V(Yellow Channel) vs LDO2_Out(Blue Channel) of PMIC. Same waveform is arrive on LDO1.

May be PMIC Start the ldo1 and ldo2 & MPU start pmic_on_req, but due to some bad configuration/something else it goes low.

pmic_vsys_5V Vs LDO2 Outputpmic_vsys_5V Vs PMIC_ON_REQ. 

Hope you got my point, please help me out in this problem.

Thank You

[weidong_sun]

Hi @milav_soni ,

    Could you send your schematic to me?

    my email is :weidong.sun@nxp.com

Regards,

weidong

[weidong_sun]

Hi,milav_soni ,

  On our IMX8MND4-EVK board, BD71850MWV PMIC is used, not BD71847, So which version of EVK did you referred to ?

  For your question: Processor Does not power up, It does not give "PMIC_ON_REQ" High signal to PMIC.

   It means that after PMIC_ON_REQ is connected to pin PMIC_ON_REQ of PMIC, the pin will be pulled down to LOW. So you can check:

1. what cause PMIC_ON_REQ to be pulled donw to LOW.

2. whether PWRON# pin is HIGH

3. whether  WDOG pin is HIGH.

Have a nice day!

B.R,

weidong

[milav_soni]

Hello @weidong_sun 

Thank You for your reply.

We use i.MX8M Nano DDR4 EVK for Processor and another interface reference.

and We use i.MX8M Mini DDR4 EVK for PMIC Reference.

And We see PWRON# Signal, it is 1.8 V and WDOG pin is low.

What is reason for PMIC_ON_REQ become Low? 

can you please suggest me?

Thank You