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Related to my last question, I decided to go with a step-down charge pump to convert 5V to 35V down to 3.3V at 10mA, due to the smaller required component size. However, I can't find a single charge pump IC rated to go up to 35V. Does anyone have any suggestions? If there are no ICs to do this, woudl there be any way of dropping 35V down to 18V with minimal loss and a small surface area?

I'd also be open to using a buck regulator, but it seems like a waste for only 10mA.

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Are there any other power rails you can tap off? And did efficiency genuinely matter? An SOT-223 should sit at ambient+50°C at 35 V @ 10 mA. – Nick T Nov 11 '10 at 16:18
@Nick T It's a power supply controller, so has to start up before the other rails and sequence/set up them. Efficiency is not really critical, so long as it's not producing too much heat. I may be able to go the linear route. – Thomas O Nov 11 '10 at 17:54

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Charge pumps tend to be oriented towards fixed ratios, so your wide input range means they are probably not a good option. For 10mA I think linear is the best bet cost-wise - may be worth seeing if you can afford to slow down the clock on the micro to reduce this by a few mA.

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up vote 2 down vote

this isn't what charge pumps are really designed for, they aren't variable input regulators but supply multipliers/dividers/inverters. They're not really designed to be fed an unregulated voltage.

Just use a buck converter or a linear regulator, examples linked.

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