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TPSM84424: Power Monitor Sequencer for multiple TPSM84424

Part Number: TPSM84424
Other Parts Discussed in Thread: TPS54824, TPSM84624, TPS54424

Hi is there a Power Monitor Sequencer for multiple TPSM84424. I am using a LTC2977 in current design, but looking for options for a new design. - Patrick

  • Hi Patrick,

    I support the TPSM84424 family of modules so I'm not very familiar with the sequencers we have available. I can really only point you to the sequencer overview page.

    I also searched our e2e forums for the LTC2977 and happened to find the post linked below which is asking a similar question but it is relatively old (from 2015). I suggest taking a look at the part discussed there and if you have any questions on it make a new post with that part number. A new post with a sequencer part number will be an easy way to get the attention of someone who works with the sequencers.

    https://e2e.ti.com/support/power-management/f/196/t/456435

    Hope this helps.

    Anthony

  • Hi Anthony, 

    I am simulating TPSM84624MOLR in webench.. I have 0.85V 1.8V 3.3V and 5V rails using 4 parts.

    My issue is I want to synq all 4 to same 300 KHz for noise (ultrasound) reasons, but  I get "Please enter a valid Sync Frequency" when I enter 300 KHz.

    This issue I am sure is that you have a fixed 0.85µH inductor, so unlike a TPS54824 (Synq at 200KHz) where I can vary inductor value, this module part requires specific sync range

    because the inductor is fixed. There is no common Synq frequency that works for the voltages I need. - Patrick

  • Hi Patrick,

    Yes, the issue is definitely related to the fixed internal inductance. With the higher output voltages the inductor ripple current goes up and the current limits can start to be hit.

    If there is a preference to use a module a way to work around it would be to add some inductance externally in series with Vout before the output capacitors. There would need to be roughly 1µH more inductance at 1.8V, 2.2µH more at 3.3V and 3.3µH the inductance at 5V. However adding some external inductance would take away one of the advantages of using a module over a converter.

  • What is the sat and rms of internal inductor?

    I assume I would need similar ratings and also any EMS advantages of module would be diminished

    Is there a similar module with higher inductance? I looked a a few alternate parts and they all use same inductor most likely

    due to modulle footprint. - Patrick

  • Unfortunately, no, there are not any similar modules with a higher inductance at the moment.

    The most conservative design would be to select the external inductance to be rated for the 11A overcurrent threshold. However I don't see any issue if the external inductor saturates because the inductor in the TPSM84624 module would prevent the peak currents from becoming too high. So potentially an external inductance with lower ratings could be used as long as that inductor can handle 11A without being damaged.

  • Understood. Backing up a bit.

    What I have designed for this portable ultrasound (low noise) design is 4 of TPS54824RNVR or TPS54824RNVR using Coilcraft SER1360 SER1390 for best efficiency. This design (size of a small book) has no fan, just heat spreader and it is used around water on dairy. A Xilinx Ultrascale+ XCZU3CG-1SFVC784E is main part, but there are also TI Pulsers and AFE for 32 channels. See Attachment. - Patrick5483.ZYNQ Power_Supply _ SHEET04 - L.pdf

  • Thanks for the details. I recall working with you on this a few years ago. Could you also give some details on why you were looking into changing to modules?

    For your use case where you want to keep the fsw as low as possible to minimize power dissipation as much as possible, the discrete solution with the TPS54424 and TPS54824 will most likely work the best.

    If you are trying to reduce the board space the power takes up, I wonder if you might be able to reduce the inductance to allow you to use smaller inductors. For example the 5V output the TPS54424 itself would work fine with a 4.7µH inductor. The trade off would be more AC loss in the inductor and more output voltage ripple due to the higher ripple current in the inductor. However I'm sure both of these tradeoffs are ones you want to be careful about making in this design.

    Is the 200kHz fsw only for minimizing power dissipation or is there some frequencies you are trying to avoid as well?

    Another option I considered mentioning earlier to try to allow the use of the modules would be to have multiple sync frequencies that are multiple of each other. For example 400 kHz for the 0.85V, 800 kHz for the 1.8 V and 3.3V, and 1200 kHz for the 5V. But I had figured the 1200 kHz option would end up with more power dissipation than your application can deal with. WEBENCH estimates a 16 °C temp rise for the 5V output at 2A with 1200 kHz fsw.

  • This clarifies my options. TPS54824 it is for this design with Zynq Ultrascale+ and no fan. Thanks for your quick response. - Patrick