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IWR6443: Power Considerations

Helgard Oosthuizen
Prodigy 20 points
Part Number: IWR6443
Other Parts Discussed in Thread: LP87745, IWR6843LEVM, IWR6843ISK, TPS62912, TPS628502

Hi

I am looking at power options for IWR6443. The design should mostly prioritize noise performance, but keep an eye on power efficiency and thermal. I have a few questions. I tried to find most answers on the forums so if I missed a post you can just direct me as well!

  1. The LP87745 looks attractive because you can extend the switching frequency outside of the band. Although we see the switching frequency peak we will likely be able to handle it though. In what situations would TI likely recommend this part?
  2. With a well-designed output filter, is there any advantage to using LP87524J (as used on IWR6843ISK) compared to using discrete bucks (such as TPS62850x used on IWR6843LEVM) on radar performance except for practical advantages such as smaller footprint, BOM, integration and configurability?
  3. If using discrete bucks in the design would it be preferable/recommended for best performance to consider a part like TPS62912?
  4. When using 1.8V IO voltage it would still be recommended to have a separate supply (probably just LDO) rather than using the 1.8V analog supply for IO?
  5. SWRA577A suggested ~2dB SNR improvement by using an LDO at RFIN. If using an LDO, would TPS7AF5x be the recommendation? Internal LDO does not suffice.

Thank you for your time!

  • 0
    TI__Expert 8750 points

    Hi Helgard,

    Please allow me 24 hours to look into all the PMIC and buck regulators and suggest the best PDN for the design.

    There will shall be a tradeoff between the smaller form factor, cleaner solution for PMIC w.r.t. to cost optimization for discrete DC-DC regulators.

    • In case of IWR6443 we would need four supply rails, hence having a single PMIC instead of 4 discrete DC-DC regulators would be a better solution.
    • I would not recommend having a LDO as it might not meet the peak current and ripple specifications requirement for 1.8V and 1.2V supply rails. 
    • The TPS62850x has a higher switching frequency up to 4MHz which is suitable for mmWave applications. It also supports Spread Spectrum Clocking, when SSC is enabled, the switching spreads within in a band of frequency which helps in mitigating any spurs or emissions. Also supports pin programmable PFM/PWM modes which is helpful in high output voltage accuracy and reduced ripples. But you will need four discrete DC regulators.

    I shall check between LP87745 and LP87524J and comeback.

    Regards

    Ankit

  • 0 in reply to Ankit Mohanty
    Prodigy 20 points

    Hi Ankit

    Thank you for looking into the different options! Just some additional information:

    • The smaller form factor for the PMIC/Discrete buck should not be too much of a consideration, I think I will have space.
    • Sorry yes, for the LDO addition, I only meant on the 1V rail. Specifically asking since it looked like it improved SNR on SWRA577A
    • I believe TPS62912 does spread spectrum as well, it just has a lower frequency.

    Thanks again for your time!

  • 0 in reply to Helgard Oosthuizen
    TI__Expert 8750 points

    Hi Helgard,

    LP87745 looks like a better solution as the switching frequency can be extended outside of the IF band reducing the need of passive filtering. But it might be an overkill as might not need the fifth supply rail of 5V (boost converter). Also, it lacks Spread Spectrum Clocking which helps in reducing EMI/EMC. But if form factor, BOM is not an issue, and EMI/EMC factors can be taken care you can go ahead with LP87745.

    Otherwise, I would recommend LP87524J with proper filtering as used in IWR6843ISK.

    Regards

    Ankit

  • 0 in reply to Ankit Mohanty
    Prodigy 20 points

    Hi Ankit

    Sorry, I completely missed your reply! Thank you for the feedback, I think I will not use LP87745 then.

    Would it still be preferred to use LP87524J over discrete bucks if BOM and form factor are not an issue? 

  • 0 in reply to Helgard Oosthuizen
    TI__Expert 8750 points

    Hi Helgard,

    If BOM and form factor are not an issue I would recommend using discrete DC DC regulator "TPS628502" for 1V, 1.8V and 1.2V as it provides an advantage of pin programmable Forced PWM/PFM mode instead of auto Forced PWM/PFM mode in LP87524J. Also, you may use LDO for 3.3V supply which has lenient peak current and ripple requirements.

    Regards

    Ankit

  • 0 in reply to Ankit Mohanty
    Prodigy 20 points

    Hi Ankit

    Thank you for your reply! TPS628502 sounds good.

    To clarify, do you think there is much performance benefit regarding SNR in adding an external LDO like TPS7AF5x on the 1V RF rail? SWRA577A suggested an ~2dB improvement in SNR? 

    Thanks again for your time!

  • +1 in reply to Helgard Oosthuizen
    TI__Expert 8750 points

    Hi Helgard,

    What is the source you will be generating all the supplies from?

    The main factors that are constraint to using a LDO are the peak current requirement of 2A-2.5A and the LDO settling time.

    But "TPS7AF5x" should be capable to meet the current requirements. Kindly check the Load Transient Response for "TPS7AF5x" if the transient response is good. You can use TPS7AF5x for 1V supply.

    Regards

    Ankit

  • 0 in reply to Ankit Mohanty
    Prodigy 20 points

    Hi Ankit

    It will just be USB or Battery.

    My concern with the LDO is also transient response, but was just curious about a possible performance increase!

    Thanks again Ankit, I think this answers everything.