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Need a lpt of different supplies but have no real space....

John Jarvo
Prodigy 60 points
Other Parts Discussed in Thread: TPS63020, TPS61093, TPS61175, TPS61085, TPS62110, TPS54160, TPS54231, TPS54240, TPS65131

Hello.  I am new to this forum, but could use some advice from someone who has been down this road....

Need +/- 12 volts (at 300mA for each rail).  Also need 3.3 volts at 500ma and 5 volts at 500ma.  Also need 1.8 volts for interfaces to the OMAPs processor.

Been looking at various TI parts (some are in the design library, some are not).

Looking at using the TPS63020 for the 3.3V and 5V rail (Note: The TINA has this as a model, and I am running sims now)

Looking at using the TPS61093 (2 of) for the +/- 12 volt rails. (Note, no model in TINA, and no part in TI's SwitcherPro)

Would really appreciate some thoughts from users, and my final PWB size is very small (4 square inches).  I do have some height, but not a lot.

And, just to make it more interesting, I have to get this out quickly.

Anyone has some thoughts on this?  Is there a faster way?  A model for the TPS61093?

Thanks in advance,

AL

 

 

 

  • 0
    TI__Guru**** 150870 points

    What is your Vin?  This will determine which parts you can use for your application.

    Note that we have a power quick search at power.ti.com that can quickly guide you to which parts fit your requirements.

    All of the parts you mentioned and most of our parts have evaluation models.  These put the parts on a PCB with all the external components needed.  This allows you to quickly test your solution with these EVMs.  Then, you can copy those designs and the layout to have a no risk implementation in your final system.  This is much faster and easier than building your own board for a first pass test.

    What are you trying to simulate?  All of the parts you mentioned have detailed datasheets which walk you through a typical design.

  • 0 in reply to Chris Glaser
    Prodigy 60 points

    Hey Chris.  Thanks for this.  My Vin is a lithium ion cell with a typical Vin of 3.7 volts.  However, I also want to be able to utilize 5 volts as well....

    I did notice that there are evaluation boards for the two products I was looking at, and the fact that there are design apps in the datasheets.  However, I was hoping just to utilize the designs from the datasheets and simulate them to ensure that they will do what I need.

    Assuming that I do not have time to wait for evaluation boards (I have no idea how long they would take to come in), do you recommend just using the layouts and designs in the datasheets?

    Thanks for such a quick response Chris

    AL

     

     

     

  • 0 in reply to John Jarvo
    Prodigy 60 points

    Hey Chris.  I was wondering if you could lend your expertise on my +/- 12V stuff.  I think the 61093 will do the job, but could not seem to find out if there is any minimum current that has to be drawn for the switcher to work. 

    Thanks,

     

    AL

  • 0 in reply to John Jarvo
    TI__Guru**** 150870 points

    Yes, if you want to utilize both a lithium cell and 5V input, then the TPS630xx products are right for the 3.3V and 5V rails.  The TPS63020 is the largest current one in this family and is much larger than you need.  Any of the TPS630xx devices will support the currents that you listed.

    Your 1.8V, I assume, is a low current supply.  For this, I would recommend a simple and small LDO.  We have over 1 thousand to choose from, so you can pick the smallest one that you are able to solder onto your boards.  The TPS72718, TPS72018, and TLV70518 are super tiny LDOs that might work depending on your current needs.

    Per Figures 2 and 3 in the TPS61093 datasheet, I don't think you will be able to get 300 mA out at 12V.  And the negative output is unachievable with a regular boost converter.  You would need to set it up as a flyback to get a negative voltage.  For just the positive output only, you could use the TPS61085/6/7 or the TPS61175.

    But with this app note, http://focus.ti.com/lit/an/slva369/slva369.pdf, you can use a buck converter to generate the +/-12V rails.  How confident are you that you need 300 mA on both outputs?  When configured as in the app note, the converter would need to start at 3V in (your minimum input voltage I assume) and have a current limit of at least 3A.

    You could also do an inverting buck boost for the -12V only using the TPS62110.  It can do the current but won't be guaranteed to start at 3V.

    The EVMs ship by the next day and ship overnight I believe.  So, if you're in the US, you get them within 2 days usually.  Overseas, not sure.  But it's still quicker than it would take to have a PCB made.

    For your very standard circuit needs, you can just copy the datasheet schematic and EVM layout.

  • 0 in reply to John Jarvo
    TI__Guru**** 150870 points

    No, the TPS61093 does not have a high enough current limit to produce 12V at 300 mA from a 3V source.

    None of our switchers require a minimum load, so no worries there.

  • 0 in reply to Chris Glaser
    Prodigy 60 points

    Hey Chris.  Thanks very much for this. 

    Thanks to you, I have implemented the TPS630XX series for my "heavy" supplies.

    Also, I reveiwed the supplied app note, and it seems to be the thing that I need.  I am certain that the most current I will require at +/- 12V is about 200mA, so I thought that 300mA would give me some margin (our product end-user requires a lot of reliability).  The 3 Volt minimum input voltage is a must, so I have a concern with the fact that the TPS54160 has a minimum input of 3.5V.  Except for that, it seems to do the job.  Do you have any other suggestions for this +/- supply?  I really need to meet the 3 volt minimum.

    Thanks again Chris, you are certainly helping us move forward on this....

    AL

  • 0 in reply to John Jarvo
    TI__Guru**** 150870 points

    That app note can also work with the TPS54231 family of devices, but these also require 3.5V for the input.  So, you have a few options:

    The TPS54240 (you would want to use this one as it has the higher current limit that you need) has an internal UVLO at 2.5V nominal.  Once the IC starts, its ground will become the negative rail and decrease.  Thus, the voltage across the IC (the input voltage that it has) will increase.  So, the only issue is starting at 3Vin.  Once it's up and running, you are good to go.  The advantage of this is that this is the most straightforward solution and has an EVM: http://focus.ti.com/lit/ug/slvu374/slvu374.pdf The disadvantage is that we can't guarantee that you will start at 3V.  Most likely you will, but we can't guarantee it.

    The other option is to use the TPS65131 for both rails.  I think you just barely meet your 200 mA need on the negative rail at 3V in.  So, this would be the best solution.  Be sure and follow the EVM layout exactly with this IC as it is intensive.

  • 0 in reply to Chris Glaser
    Prodigy 60 points

    Hey Chris.  Just finished reviewing the datasheet on the TPS65131 for the +/- 12V rails, and it will be close from a current POB, but I think it will work.  Wondering if you could tell me where I could find a layout for this design....

    BTW, the LDO's are indeed the way to go for the 1.8 V interface (the interface chips don't need a lot of current to operate).

    Thanks again,

    AL

  • 0 in reply to John Jarvo
    TI__Guru**** 150870 points

    Here is the user's guide for the EVM.  It has the layout in it. http://focus.ti.com/lit/ug/slvu119c/slvu119c.pdf

    And here is the EVM: http://focus.ti.com/docs/toolsw/folders/print/tps65131evm-063.html

    I recommend using the largest inductor allowed by the datasheet to keep the ripple current to a minimum.  This will help increase the maximum output current.

  • 0 in reply to Chris Glaser
    Prodigy 60 points

    Hey Chris.  thanks for all this, and things are certainly going faster for us....

    I am using 4 switchers, and I was wondering what your thoughts were in regards to syncing them up as a noise reduction effort.  I understand that this would affect the overall circuit design, but again wondering your thoughts.

    BTW, this is a great forum for getting support from TI.  Wish we would have had this back in the day....

    Thanks,

    AL

  • 0 in reply to John Jarvo
    TI__Guru**** 150870 points

    Since none of your outputs are connected in parallel, syncing would just help you reduce noise on the input side, not the output side.  If you need your output noise to be in a certain frequency band, syncing them would help with that but it wouldn't reduce the noise on the output.  Syncing could reduce your input ripple by syncing them 90 degrees out of phase with each other.  You can't sync the TPS65131 and unless you are trying to meet some stringent EMI or emissions spec, I don't think syncing is worth it.  Especially considering your limited space.