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I'm (still) selecting parts to build a 3 to 5V boost DC-DC converter using the LTC3525-5. The board I'm planing to build is based on the typical application shown in page 11 of the aforementioned datasheet, which schematic I reproduce below:

DC-DC boost converter schematic

I'm having trouble finding the right output capacitor. The closest match I can find at my local suppliers is this 10uF X5R capacitor (JMK212BJ106KD-T) rated at 6.3V, but I think that's too close to the 5V output.

So, my questions are:

  1. Is the 6.3V capacitor appropriate for my application? If not, what would be a suitable replacement?
  2. What will be the maximum voltage I should expect at the output capacitor terminals? What would be the minimum voltage rating for such capacitor?

I tried, but couldn't find such information on the datasheet or elsewhere.

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    \$\begingroup\$ It's not great design practice but as long as the load doesn't vary violently you should be OK with a 6.3V cap. I would however consider a 5.1V zener if the load is inductive, such as a motor, just to be safe. \$\endgroup\$ – Evan Jul 14 '14 at 15:10
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I simulated your circuit using LTSpice for 3V in and 4.2V in and there was virtually zero overshoot. That means you could use 6.3V capacitors. If your local supplier doesn't have any you can always order offline. You could probably get 10V caps just to feel safe and increase the robustness of the circuit if area and cost aren't super critical to this design.

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  • \$\begingroup\$ I'm impressed. How did you simulate the circuit so quickly? If it's not too much to ask, could you simulate it at 1V in and report the results? Many, many thanks! \$\endgroup\$ – Ricardo Jul 14 '14 at 13:11
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    \$\begingroup\$ If you click the "Open this macromodel's test fixture" button it will create the commonly used topology for you. It saves a ton of time! I included a picture. imgur.com/Ra7s7bU Looks like no overshoot on 1V. If you are powering this from a li-ion battery like the note says be warned you will never have 1V in though. \$\endgroup\$ – ACD Jul 14 '14 at 13:25
  • \$\begingroup\$ I'll try to power it using one NiMH AA battery, if I can get away with it (that's why I asked about 1V in). If not, I'll use 2 AA's. I expect to draw at most 20mA from the circuit, so I think 1 AA will be fine. \$\endgroup\$ – Ricardo Jul 14 '14 at 13:29
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    \$\begingroup\$ That should work well. 20mA with 1V in is at the peak of their efficiency curve, 85%. \$\endgroup\$ – ACD Jul 14 '14 at 13:56

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