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LP87524J-Q1: IC not Powering UP

Shubham S
Prodigy 50 points
Part Number: LP87524J-Q1

Tool/software:

Hi,

I am trying to power up LP87524J PMIC, I am observing that nINT pin is showing 0V meaning that there is some fault or Reset has occurred.  I am  unable to understand why there exists a fault  and which one so that I can debug it.

I checked VANA is 5V i.e above threshold,

nRST is pulled up to 3V3,

nGOOD is also connected to 3V3.

I am trying to replicate it with AWR1843EVM Board, I have shared my schematic of PMIC part

regards,

  • 0
    TI__Genius 16350 points

    Hi,

    Your thread has been assigned to the device expert. However, the device expert is out of office due to holiday in US. Meanwhile, I am trying to support. 

    If the nINT is low that means some interrupts are pending. You can read INT_TOP1 and INT_TOP2 registers to read the interrupts and get to know what is pending. You can see the summary of interrupt signals in data sheet. 

    To my understanding device is powering up so you have all the rails up only issue is with nINT being low. Is that correct?  

    I have had a brief look at the schematic. 

    1. C14 doesn't seem to be connected to GND at VIN_Bx pin. And I see only one 10µF input capacitance. Where as in the datasheet it is recommended per phase. See below highlighted from Datasheet. 

    2. VANA filtering cap is recommended to be 100nF not 22µF. Or you can place 0.22µF as well. 

    3. Recommended snubber 3.83 ohm series resistors are missing. 

    4. Can you also check in the layout if whether PMICVIO_3V3 (supply from 5V) is shorting with PMIC_3V3 ( which is basically output from BUCK0) at PGOOD pin connections. From the schematic it looks like it is shorting but you need confirm in layout. These are both separate supplies and should not short. 

    Regards,

    Ishtiaque

  • 0 in reply to Ishtiaque Panhwar
    Prodigy 50 points

    Hi Ishtiaque,

    Yes , nINT being LOW, we reconnected our new IC, now I am seeing that nINT goes High, EN1 is high but still PGOOD is low and no voltage is seen.

    as we aren't using regulators at output we aint using snubber. and also SDA and SCL pins are left on float as they aren't connected to MCU. Should they be pulled up externally?

    PMVCIO_3V3 is now not shorting with PMIC_3V3 we removed the resistors in between, now PGOOD is open.

    regards,

  • 0 in reply to Shubham S
    TI__Genius 16350 points

    Hi Shubham

     If PGOOD pin is low it means there is some problem with BUCKs.  Did you try to correct the snubber circuit? 

    Shubham S said:
    PMVCIO_3V3 is now not shorting with PMIC_3V3 we removed the resistors in between, now PGOOD is open.

    Which resistor have you removed? In OTP it is Open-drain configured so it should have pull up to PMICIO_3V3 at least. 

    And another thing that I noticed is that compared to your design schematic, in AWR1843EVM schematic, there is 2x22µF local capacitance on 1.2, 1.0 and 1.8V where as in your schematic it is only 1x22µF. If the load on RF is heavy and capacitance is less because of that voltage rails can be dipped down may generate UV. There could be possibility of that scenario as well. 

    What is the state of BUCKs ? does all the bucks do not power up?

    Regards,

    Ishtiaque