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

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

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

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

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

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

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?

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

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 Ankit,

Thank you so much for your answers.

Best regards
Yasuaki