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I need to take unregulated li-ion voltage (3.3-4.2 V) and convert it to regulated DC around 6-12 V. The load is a 555 timer driving a component that needs 3V very-low-current AC.

The application is insanely space-constrained. At the most, there is room for a SOT-23 and two bypass capacitors, and that's it.

All of the boost regulators that I've seen require an inductor, three resistors, a capacitor, and a diode, not even including the bypass caps. There simply is not room for all of these external components.

Is there some circuit I can make, no matter how many corners need to be cut, that will let a boost regulator do its job "good enough" to drive a 555, without all these external components?

I'm guessing I don't really need the load-side bypass cap, so ditching that should make room for one other component.

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  • \$\begingroup\$ The 555 I have is a SOT-23 that only needs 2 external components (1 cap & 1 res) so I think that's already as small as can be. \$\endgroup\$ Nov 8, 2013 at 23:38

3 Answers 3

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As an extension to what Madmanguruman suggested, there is also an Small Package Step up IC TPS60150 that TI offers and outputs a 5V regulated output for any Vin between 2.7 & 5.5V.

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  • \$\begingroup\$ Wow that is small! \$\endgroup\$ Nov 9, 2013 at 0:30
  • \$\begingroup\$ This chip can boost to 5V, but I need to boost to at least 6V. Do you know any 6V solution? This should be feasible because 6Vout is < 3.3Vin * 2, allowing the use of a switched-capacitor voltage doubler. \$\endgroup\$ Nov 12, 2013 at 6:10
  • \$\begingroup\$ I dont think so there is an IC which does exactly 6V, however a chip like this cds.linear.com/docs/en/datasheet/10178ff.pdf can step up to 10V, which can be passes through a divider(which will not be efficient). \$\endgroup\$
    – Sherby
    Nov 12, 2013 at 7:01
  • \$\begingroup\$ Also LTC1044 chip : cds.linear.com/docs/en/datasheet/lt1044.pdf can be used as a voltage doubler, which should help. I have not tested it though. \$\endgroup\$
    – Sherby
    Nov 12, 2013 at 7:05
  • \$\begingroup\$ Both of those are really big though :-( \$\endgroup\$ Nov 12, 2013 at 7:58
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Consider a switched-capacitor step-up circuit like the LM2750 - you likely won't find anything smaller.

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  • \$\begingroup\$ Very good idea to look for "switched-capacitor" chips, thank you very much. I can find a lot of switched-capacitor boost regs that boost to 5V, but I need to boost to at least 6V. Do you know any 6V solution? This should be feasible because 6Vout is < 3.3Vin * 2, allowing the use of a switched-capacitor voltage doubler. \$\endgroup\$ Nov 12, 2013 at 6:09
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    \$\begingroup\$ There is an LM2750 option with adjustable output, at the expense of two resistors to set the voltage level (which could be 0402 size). \$\endgroup\$ Nov 12, 2013 at 13:47
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Are you short on area, or on volume? If you have room above or below your board, i.e. spare volume, you might be able to fit a boost converter on a parallel or perpendicular PCB.

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  • \$\begingroup\$ Good idea, but sadly I'd say "both area and volume". The space available is about 3x5mm area x 3.5mm height (but this free space is only on one side of the board). \$\endgroup\$ Nov 8, 2013 at 23:34

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