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IWR6843AOPEVM: IWR6843AOPEVM: No device access via USB

Thomas Pham
Prodigy 30 points
Part Number: IWR6843AOPEVM
Other Parts Discussed in Thread: LM2833, IWR6843AOP, LP87745, IWR6843, LP87745-Q1, UNIFLASH

Hello there,

I’ve designed a radar board based on IWR6843AOPEVM. On my design, I simplified the EVM board by removing break-away parts, using bigger components to make convinience for the SMT process. The biggest change in my design is replacement of PMIC. Due to scarcity of PMICs LP87524JRNFRQ1, I had to replace them by PMIC LP877451 to supply 1.0V, 1.2V, 1.8V voltage and LM2833 to supply 3.3V. After SMT process, all 4 outputs voltage are quite good.

But I got a problem there: after SOP config, my boards are unable to connect to my computer. When connecting the USB port to the conputer, the USB status LED blinks 4 times and the PC cannot recognize the device.

When I using oscilloscope to mearure NERR_OUT pin, on the IWR6843AOPEVM board, the output voltage is 3V3, but on my own board, they are 0V.

This is my schematic, can you help me figure out what's wrong with my board?

Thanks so much

schematic_IWR6843_newPMIC

  • +1
    TI__Mastermind 25835 points

    Hello,

        NERROR low indicates there is fault in the system.  Is it possible to isolate the NERROR from the PMIC and IWR6843AOP?

    Also isolate the NRESET from the PMIC and apply reset externally please ensure NRESET is applied when all the supply voltage to the mmWave device is stable. 

    Thanks and regards,

    CHETHAN KUMAR Y.B.

  • 0 in reply to CHETHAN KUMAR Y.B.
    TI__Genius 12735 points

    Hi Thomas,

    I have assigned this thread to the expert for the LP8774 family, however he is out of office until Monday. Please accept a delay in response.

    Best regards,

    Layne J

  • 0 in reply to CHETHAN KUMAR Y.B.
    Prodigy 30 points

    Hello CHETHAN KUMAR Y.B.,

    I've removed the 0Ohms resistor that connected NERROR of IWR and PMIC, so, the NERROR from PMIC is isolated from IWR. 

    After removing these resistors, the voltage between pin NERR_OUT, NERR_IN of IWR6843AOP and GND is 3V, and when all the supply voltage to the mmWave sensor is stable, the voltage between NRESET pin of IWR6843AOP and GND is 2.5V (all unused pin in PMIC is connected follow LP87745 datasheet guidance). I think the voltage drop is due to the pull-up resistor, so it's not too critical.

    But the most important things is that I still unable to connect to USB port.

    Hope to hear from you soon,

    Thomas

  • 0 in reply to CHETHAN KUMAR Y.B.
    Prodigy 30 points

    sorry, I accidentally marked this issue as resolved.

  • 0 in reply to Thomas Pham
    TI__Expert 4985 points

    Hi Thomas,

    So based on your posts the PMIC powers on correctly, right? I took a look at the schematics for the PMIC portion.

    • There is no need for the second stage LC filters with LP87745-Q1 since the device is switching above the IF band of IWR6843.
    • Boost should have larger input capacitor. 4.7 µF capacitor recommended instead of 2.2 µF.
    • No need for NRSTOUT, NINT pull ups. The preview OTP of LP87745-Q1 has the internal pull ups enabled for these pins.
      • Is the voltage divider on NRSTOUT needed?
    • NERR is an input on LP87745-Q1. It should not be loading the IWR side. 

    Best regards,

    Samuli Piispanen

  • 0 in reply to CHETHAN KUMAR Y.B.
    Prodigy 30 points

    Dear CHETHAN KUMAR Y.B,

    I have already connected my own boards to my computer via USB port. There was some error with the CP2105, but i fixed them. Now, i can connect board via USB. 

    But I still can't load the firmware into the board using Uniflash. When loading the firmware with uniflash, a message appears that the com port is openning, then the program crashes. 

    I tried following your advice: NRESET, NERR and NRSTOUT in PMIC is isolated with IWR6843 by removing resistors, and of course, those pins on the PMIC are all grounded or floated as per the instructions in the datasheet of LP87745. I used the oscilloscope to measure the output voltage values ​​of the PMIC, and those values ​​are completely normal. So I think the PMIC isn't the problems. 

    And one more things, there is a mistake in my measurement. the 3V3 is the voltage between NERR_MCU of PMIC, and the NERR_OUT is still low indicates

    Do you have any suggestion to fix this bug? Can you please check my schematic?

    Thanks for reading, let me your opinion on this issue.

    Thank you

    Thomas Pham said:
    the voltage between pin NERR_OUT
  • 0 in reply to Thomas Pham
    TI__Expert 6700 points

    Hello Thomas,

    Samuli should be able to get a response to you by Monday. Thank you.

    Regards,

    Alex

  • 0 in reply to Alex Saenz
    Prodigy 30 points

    Dear Alex,

    As I mentioned above, the PMIC, to my way of thinking, is working correctly, so I think I much prefer to hear opinions from the expert for the IWR6843. 

    But, if the problem is in the PMIC, such as the transient process, i would like hearing about expert for the PMIC.

    Thank you so much

    Thomas

  • 0 in reply to Thomas Pham
    TI__Expert 4985 points

    Hi Thomas,

    Yes, I agree that the PMIC seems to be working correctly and the issue is on the radar side. I am assigning this back to Chethan.

    Best regards,

    Samuli Piispanen

  • 0 in reply to Samuli Piispanen
    TI__Mastermind 25835 points

    Hello Thomas,

         If the NERROR_OUT coming from the mmWave sensor is low, then there seem to be a fault in the system, Without addressing that you will not be able to interact with the mmWave sensor.  Typically NERROR fault assertion could occur for multiple reasons for example: 1) It could be supply: Supply not stable during the power up (Please refer below timing diagram, please confirm all the supplies are within the datasheet limits before the NRESET assertion)

    2) All the voltage rails need to be within the datasheet limits, If the voltage levels are below or above the datasheet limits then voltage monitors within the chip will assert NERROR.

    3) Right SOP assertion and NRESET release need to take place.  Please review the reference schematic, with the Do not install options also. 

    For example, on the one of the boot mode pins, AR_PMIC_CLKOUT_SOP2 PMIC_CLK should not be connected, It's DNI (Do not Install option),

    However it's connected in your board, this need to be removed, This will interfere with the SOP boot mode.

    During the power up before SOP and NRESET assertion mmWave sensor expect all the voltages to be stable as per the datasheet, 

    Please review right SOP[0,1,2] mode and NRESET release on the scope. 

    Thanks and regards,

    CHETHAN KUMAR Y.B.

  • 0 in reply to CHETHAN KUMAR Y.B.
    Prodigy 30 points

    Dear CHETHAN,

    Thank you for your suggestion. I have check all 3 cases that you mentioned.

    First, about AR_PMIC_CLKOUT_SOP2 PMIC_CLK, I have removed the 0 Ohms resistors that connected them, and it seems like the board still doesn't work.

    So, I have checked all voltages rails value at the startup period. 

    3.3V VIO of the IWR6843AOP

    1V RF1 of the IWR6843AOP

    1V8 IO Supply

    1V2 Rail

    I have also tried to reset the device externally by pulling the NRST down and release before but it didn't work. 

    Hope to hear from you soon,

    Thomas

  • 0 in reply to Thomas Pham
    TI__Mastermind 25835 points

    Hello Thomas,

       Thanks for sharing the voltage levels, However,  we cannot just look at individual rails separately as it doesn't confirm that all the supplies are stable before NRESET release as per datasheet requirement. 

     For example, 3.3V supply is directly being fed from separate DCDC (LM2833XSD), This causes 3.3V I/O supply being applied before other supplies are being fed.  

    In that condition NRESET need to be held low till all the supplies are being stable (Please refer to above timing diagram from the datasheet), But NREST will be released quickly by below RC time constant of the circuit, before PMIC supplies all the rest of the rails. 

    However other supplies are still yet to stabilize as they are coming through PMIC, This potentially could cause NERROR as all the supplies are not available at the time of NRESET release.  

    Perhaps, you may have to provide large RC delay such that NRESET is released after all the supply voltages are stable. Or hold NRESET low through external interface till PMIC provides all the rails.

    After the supplies are stable, for flashing mode 101 (PMIC_CLKOUT_SOP2, SYNC_OUT_SOP1, TDO_SOP0) signal need to be asserted and external NRESET need to be applied.  This sequence is important to register the boot mode by the bootloader. After NRESET there should not be NERROR for proper functioning of operation.  

    Thanks and regards,

    CHETHAN KUMAR Y.B.