App note: A microwatt charge pump boosts 1 V to 1.8 V at 90% efficiency, providing “Always On” standby power for microcontrollers


Interesting app note from Silicon Labs on high efficiency charge pump utilizing their nanopower TS1001 op amp. Link here (PDF)

Boosting the output voltage of common alkaline button-cells to at least 1.8 V needed by microcontrollers provides an “always on” standby power source sufficient for low-power oscillator interrupt/sleep state operation. Two ultralow power op amps are used in a charge pump configuration to double an input voltage, creating an output voltage of approximately 2x the input voltage. Output currents up to 100 µA are available at 90% efficiency; even load currents as low as 10 µA achieve 80% efficiency, beating commercially available charge pump ICs and inductorbased boost regulators.

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  1. Farnell says TS1001 is no longer stocked. Not on RS. Digikey says it’s obsolete. That said, there are a lot of nanoamp-class parts on sale (but rated for >=1.4V). Perhaps the sales of a 0.65V Vmin part is poor. Maybe people designed things differently instead of using such a part (quite possibly a premium, single-sourced part).

    Rather complicated for a voltage doubler or for a hobbyist to incorporate into a project. Easier to use a boost IC with a low-load PFM or pulse-skipping or PWM-hysteresis mode.

    A product needing one LR44 is a cheap product, one will never be able to justify this circuit. They would use two LR44s instead. Note that many motherboard manufacturers have moved to CR1220 from CR2032. Lithium coin cells (which runs from 3.3V down to about 2.9V) enables one to drop the LDO or switching IC losses.

    But why even pick two LR44? (Unless you are manufacturing very cheap products.) CR2032 is readily available, as are appropriate cell holders. My biggest hobbyist reason for not using alkaline coin cells is that they can leak and corrode badly (maybe not with expensive coin cells, but who buys expensive cells like Maxell for hobby projects?) (how many such corroded cells have you pried out of cheap childrens’ toys?) while lithium cells stay at >=3.0V for their entire useful life and old cells often corrode near the seals (usually less badly compared to alkaline coin cells).

  2. Using an alkaline coin cell down to 1.0V or under is a very bad idea anyway, unless you as the designer or manufacturer don’t care about corroded battery cells. In cheap toys, the buyer is expected to throw away the item, which is already about at the end of its design life and may fall apart any time. The alkaline battery chemistry is fundamentally more corrosive than lithium primary coin cells etc. It’s all about costs, pricing, economics.

    I have a cheap EC meter with a 2x LR44 cell holder which gave trouble after a few months or so. The usual problem with cheapo products. Luckily, as an electronics hobbyist, I modified the battery end and glued on a CR2032 holder, soldered wires to the contacts, and now it’s super reliable. Folks without a soldering iron are not so lucky.

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