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TPS63001 and CC3200 3.3V / 1.8V

Philip Kristament
Prodigy 220 points
Other Parts Discussed in Thread: TPS63001, TPS62421

Dear Power Supply Boffins,

Before I bother you with my question I would like to point out that phase one of my business plan allocates a large chunk of cash towards engaging a firm of professionals to do the PCB layout and design. All I am trying to do is ensure that my early investors don't receive a letter stating that due to an unfortunate oversight the project is a bust. So long and thanks for all the fish.

Also, the device is a wearable and forms only part of a much larger system. It is critical the device be available as close to 24/7 as possible and therefore discharged batteries will be swapped for fully charged ones when required. The device cannot even be left charging overnight.

Having satisfied myself that a cellphone-type Lithium-ion battery will be suitable for the device (post http://e2e.ti.com/support/wireless_connectivity/f/968/p/386215/1362355.aspx#1362355) and that the TPS63001DRCR 3.3 V buck/boost with a Murata 100 µF Capacitor (GRM31CR60J107ME39L 6.3V 20% X5R) will PROBABLY allow me to use a single supply for both digital and analog (with appropriate bypass capacitors as per reference designs) I am left with the following question.

I have a number of components which require 1.8V supplies, both for analog and also digital I/O.

I have considered the following possibilities...

(a) Two batteries. Ruled out because of size constraints and because the device needs to monitor the battery and inform the wearer with time to spare that a discharged battery needs replacing. Can't have one battery running flat and rendering the device inoperable.

(b) A buck/boost that has multiple outputs with a built in LDO for the 1.8 V supply. Ruled out because the only such regulators have a quiescent current requirement that is too high at around 15 mA.

(c) A voltage divider. Ruled out because to obtain a sufficiently stable output voltage, the output current must either be stable or limited to an appropriately small percentage of the divider's input current.

(d) An LDO that is separate from the buck/boost (don't know the implications really). Ruled out because to output 1.8V an LDO linear regulator needs to have an input voltage of 2.8V minimum, which is higher than the minimum voltage that the buck/boost requires to still output 3.3V (which is 1.8V).

(e) An LDO that has as it's input the 3.3 V from the buck/boost and lowers it to the required 1.8V. As the only possibility I haven't ruled out it seems a a waste to dissipate 1.5 V as heat.

Is there an option I haven't come across in my research?

Any input would be greatly appreciated.

  • 0
    TI__Expert 7110 points

    Defining your power architecture is a very important and path-breaking step.

    Let me share my thoughts on the written above:

    • From what I understood is that your application is a wearable device, with a rechargeable power source. You need several output rails with 3.3V and at least one with 1.8V.
      To determine your power architecture, one of the first steps is to draw a power tree. This tree should contain all the voltages and the current need.
      • With the power tree, you can select the appropriate power devices.
    • I guess power dissipation is key, as you run a wearable device. Therefore a DC/DC Converter is the way to go. A LDO or even a resistive divider will waste a lot of energy.
    • Once you chose the suitable buck/boost converter, please be aware that there are more device than TPS63001 available with different voltage and current capabilities.
  • 0 in reply to Florian Feckl
    Prodigy 220 points

    Thanks for the input regarding DC/DC being the way to go.

    I ferreted out a buck that would output 1.8V X 2, the TPS62421, and have replaced the LDO in my BOM with the TPS62421 and it's inductors and capacitors. The effect on the price was an extra buck (no kidding) and on the footprint 58 sq mm with the extra 1mm added to the component dimensions as per the TI footprint calculator.

    Now as to the arrangement, I see 3 possibilities. If any of these arrangements work then I can be happy I don't need any more bucks in the BOM or an additional battery etc.

    Arrangement #1 looks so much like a Voltage Divider I am positive it is silly and won't work but have included it anyway.

    ARRANGEMENT #1 – SILLY WON'T WORK



    Arrangement #2 looks less like a Voltage Divider and so might work.

    ARRANGEMENT #2 – LESS SILLY HOPEFULLY WORKS



    And arrangement #3 is the one I'm pretty sure will work, but would probably prefer arrangement #2 if that worked.

    ARRANGEMENT #3 – PROBABLY WORKS BUT WANT ARRANGEMENT #2 ABOVE



    So can I close off the power supply side of things with one of the above arrangements do you think?  Or is my PCB footprint and cost going to go up?

    Once again, any input greatly appreciated.