IWR1843: The chip's power supply and reset signals meet the power-up sequence requirements, but the chip does not work properly.

Part Number: IWR1843

Hi team,

We designed our own radar hardware board based on IWR1843 chip.
The power supply solution used the LP87524JRNFRQ1.
When we were testing the IWR1843 boards, one of the hardware boards failed to start after being powered on, in low-temperature environments as -35 degrees.
It will start up properly above -20 degrees.
All other boards are booting properly at -35 degrees and -40 degrees.
We debugged the problematic hardware board and the 3.3V, 1.8V, and 1.0V voltages supplied to the chip.
Everything was properly.
We used an oscilloscope to measure the timing of the power supply and reset signals, which also met the manual's requirements.
(The rising edge of the nReset reset signal was about 10ms later than the VIOIN power supply)

When We measured a 40M crystal oscillator, no oscillation waveform was output when it did not start up.
We've checked that there is no problem with the matching capacitor.

So could you please tell me the specific reason for this problem?
Does it means that this chip is damage, or something else?

Regards,

Yasuaki

  • Hello, 

    We are looking into your question. Please expect a response in the next 24-48 hr. 

    Best Regards,

    Josh

  • Hi Yasuaki,

    Could you please confirm if all the components on the hardware support upto -30 degrees ?

    Regards

    Ankit

  • Hello Ankit,
    Yes, all the components on the hardware support upto -40 degrees. (Including -30 degrees)
    Best Regards,
    Yasuaki

  • Hi Yasuaki,

    A 47-nF capacitor is needed on the bandgap pin. Not having correct capacitor on this pin, can cause boot up issues, especially, at negative temperatures. Could you please confirm the recommended 47-nF capacitor part - GRM155R71E473KA88 is used ?

    Regards

    Ankit

  • Hello,
    Thank you for your reply.

    We use 220nF capacitor.
    Therefore, I understand that there is a possibility that we may encounter startup issues with our board.
    I would like to know more about this issue.
    Please provide the following information:

    1. Most of our boards do not have this problem using 220nF capacitor.
      Will these boards continue not to have this problem in the future?
    2. Does the temperature at which this problem is likely to occur vary depending on the board?
    3. Could you explain the mechanism behind this issue?

    Best Regards,
    Yasuaki

  • Hi,

    1. The boards that are working now, might not work in future as the dielectric properties of the capacitor may change at negative temperature.

    2. There is no fixed temperature at which this problem is likely to occur, this may vary from board to board.

    3. At lower negative temperature the dielectric properties of the capacitor may change leading to higher capacitance and hence boot up failure. So, it is recommended to use only 47nF capacitor part - GRM155R71E473KA88.

    Regards

    Ankit

  • Hello,
    Thank you for your prompt reply.

    I understand that the problem tends to occur more frequently as the capacity increases.
    I would like to know more details about the mechanism of this issue.
    Why does the problem become more likely with a larger capacity?

    Best regards,
    Yasuaki

  • Hi Yasuaki,

    Larger capacitor requires longer time to charge it. The device checks for VBGAP voltage for enabling the oscillator; if the VBGAP voltage does not come up within the specific time the internal RC OSC will not get enabled and power-up will not proceed.

    Regards

    Ankit

  • Hello,
    Thank you for your reply.

    Does the capacitor of the VBGAP have an impact apart from at boot up?
    For instance, would the capacitance affect the operation when there are fluctuations in temperature or power voltage?

  • Hi,

    Yes, capacitor of the VBGAP will have an impact apart from at boot up. VBGAP is used as reference voltage for all power supplies.

    Regards

    Ankit

  • Hello,
    Thank you for your reply.

    I'm concerned about the negative effects of lowering the capacitance of the capacitor connected to the VBGAP pin.
    A common problem in such cases is that the bypass capacitors no longer work, increasing noise, etc.
    What precautions should I take when reducing the capacitance of the capacitor connected to the VBGAP pin in this device?
    Also, what kind of verification do we need to do to dispel the above concerns?

    Best regards,
    Yasuaki

  • Hi Yasuaki,

    You can use the standard 47nF decoupling capacitor across the VBGAP pin which has been validated and is being used across all TI EVMs and reference designs.

    Could you please elaborate what you meant by lowering the capacitance?

    Regards

    Ankit

  • Hi Ankit,

    What I meant by "lowering the capacitance" is to change the capacitor at the VBGAP pin from 220nF to 47nF.
    I understand that the operation is guaranteed when changing from 220nF to 47nF.
    We have been manufacturing and evaluating boards with a 220nF attached so far.
    We want to change to 47nF, but before doing that, we need to confirm that the impact of this change is not a problem.
    Therefore, could you please tell us about the changes in operation and the impacts we should be aware of when changing from 220nF to 47nF?

    Also, we are verifying startup failures.
    It was advised that startup failure may occur due to "higher capacitance",
    so on the board that starts up normally, we tried replacing VBGAP capacitor with 470nF, but we could not reproduce the startup failure.
    Could you please tell us why we can't reproduce it?

    Best regards
    Yasuaki

  • Hi Yasuaki,

    The startup failure is not guaranteed to happen for higher value of capacitance but there is higher probability of failure. There were boot up issues seen for higher capacitance at negative temperature of -30, -40 degree C which was resolved by using a 47nF decoupling capacitor.

    There won't be any drastic change or impact in operation, the boot up sequence would still be the same and the VBGAP voltage will come as 0.9V as earlier. But you will see improvement in boot up time (microseconds) resolving the boot up failure issue.

    Regards

    Ankit

  • Hello, Ankit

    Thank you for your reply. I would like to ask you in more detail.

    1. Is there a method to reliably cause startup issues? If yes, could you please tell me how?

    We would like to evaluate even the minor changes that occur when we change the VBGAP capacitor from 220nF to 47nF.
    I understand the increase in voltage at startup.
    Could you please answer the following questions about the impact of changing the capacitor?

    2.1. Will there be any changes in RF transmission characteristics?
    2.2. Will there be any changes in RF reception characteristics?
    2.3. Will there be any changes in power consumption during RF transmission?
    2.4. Will there be any changes in the radiation characteristics of noise or spurious?
    2.5. Are there any other changes?
    If yes, could you please tell me what kind of changes and how much change will occur?

    Best regards,
    Yasuaki

  • Hi Yasuaki,

    1. No, there is no method to reliably cause startup issues.

    2. The answer for all the questions will be NO, there won't be any impact on RF performance or power consumption due to change of capacitor.

    Regards

    Ankit

  • Thank you for your reply.

    If the VBGAP capacitor is 47nF, would there be any issues (start-up, radar performance) due to the VBGAP capacitor in the operating temperature range from -40℃ to 105℃?

  • Hi,

    There won't be any issues start-up or radar performance due to the VBGAP capacitor change to 47nF in the operating temperature range from -40℃ to 105℃.

    Regards

    Ankit

  • Hello,

    We are planning to change the capacity of VBGAP to 47nF, but we have some questions.
    You recommend the use of GRM155R71E473KA88, but considering availability and other factors,
    we are also considering using other capacitors.
    Therefore, we would like some information about the selection of capacitors.

    1. If we use GRM155R71E473KA88, will there be no startup issues across the entire temperature range?
    2. What is the capacitance value of the VBGAP capacitor above which startup issues are likely to occur?
    3. What is the minimum capacitance value of the VBGAP capacitor?

    Best regards,
    Yasuaki

  • Hi Yasuaki,

    1. For TI testing and validation, we have not yet encountered any startup issues across the entire temperature range GRM155R71E473KA88 for VBGAP.

    2. There are no exact specifications for the same. In earlier EVMs where 220nF cap was used startup issues were encountered.

    3. There are no exact specifications for the same. No startup issues were encountered for 47nF.

    Regards

    Ankit

  • Hello, Thank you for your reply.

    We would like to select a capacitor equivalent to GRM155R71E473KA88.
    If the following performance is the same as GRM155R71E473KA88,
    can we assume that there will be no startup issues even with other capacitor products?

    • Capacitance: 47nF±10%
    • Temperature characteristic: X7R

    Are there any other performance requirements necessary to avoid startup issues?

  • Hi Yasuaki,

    Yes, these specs should be OK. Please ensure operating temperature -55 degrees C to 125 degrees C.

    Regards

    Ankit

  • Hello, Ankit
    Thank you for your reply.
    We measured the VBGAP voltage of our hardware board. We have questions regarding the voltage waveform.

    Fig.1 shows the rising waveform of the VBGAP voltage when a 47nF capacitor is connected to the VBGAP pin.
    Is it correct behavior that the VBGAP voltage increases in two steps?

    Fig.1 VBGAP Voltage (C=47nF, T=+25degC)

    Whether the capacitor on the VBGAP pin is 47nF or 220nF, there is not much difference in the time it takes for the VBGAP voltage to fully rise (Fig.2 and Fig.3).
    This is because if the capacitor on the VBGAP pin is 47nF, the VBGAP voltage will rise in two steps.
    This difference is not purely due to capacitance, so we are worried that it will cause startup problems.
    When the device checks the VBGAP voltage, How many is the threshold voltage and when is the judgment timing?
    Are there any temperature characteristics in the threshold voltage and judgment timing?

    Fig. 2 VBGAP Voltage (C=47nF, T=-35degC)

    Fig. 3 VBGAP Voltage (C=220nF, T=-35degC)

    Best regards,
    Yasuaki

  • Hi Yasuaki,

    The two-step rise in the VBGAP voltage in case of 47nF is an expected behaviour. This is to avoid any reliability issues by doing a fast start up and slow start up after settling to avoid any boot failure. If you check the graphs the rise time in case of 220nF at negative temperature increase which wrt 47nF might cause boot failure.

    The validation has been done for 47nF decoupling capacitor across VBGAP across all PVT corners. The threshold voltage and judgment timing are independent of temperature characteristics.

    Regards

    Ankit

  • Hello Ankit,

    Considering the behavior of the voltage increasing in two steps to avoid boot failures,
    does this imply that a monotonic increase in voltage, as shown in Fig. 3, is problematic?

    Best regards
    Yasuaki

  • Hello Yasuaki,

    The monotonic increase in voltage does not necessarily imply to be problematic.

    Regards

    Ankit

  • Hello Ankit,

    Thank you so much for your answers.

    Best regards
    Yasuaki