Keynote

Marketing Malarkey and Some Truths About Ultra-Low Power Design

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01:09:21

EOC 2023

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Jack Ganssle

Jack Ganssle is an internationally-recognized embedded systems engineer, author and speaker. He designed some of the very first embedded systems. He started three high tech companies, built or managed the development of over 100 embedded systems, and now advises companies, lectures, and writes about embedded systems. He was the only embedded person on NASA's Super Problem Resolution Team, created by the Columbia Accident Investigation Board to harness the expertise of highly-respected people from outside the agency. He has worked on many classified government projects. Full bio here.

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Hardware Low Power Microcontroller Design Cycle

Keynote

Marketing Malarkey and Some Truths About Ultra-Low Power Design

Jack Ganssle

01:09:21 EOC 2023

Jack Ganssle

01:09:21

Many systems need to run for years from small batteries. Vendors offer many solutions and even more promises. Alas, too often these are, at the best, wildly optimistic. Pick an MCU which only needs one electron a year to remain in a sleep mode and your system will still likely drain the battery in months.

This talk will present the results of 18 months of experiments on battery life, MCU sleep currents, and “sneak” circuits that drain charge from batteries. It is complemented by engineering analysis of real-world systems and what their actual power requirements are. Does PCB contamination effect battery life? Can a big capacitor give a millisecond power boost? What is the effect of temperature on these decisions?

The answers are surprising, and the bottom line is that none of us will achieve the battery lives touted in the trade press.

To achieve years of operation from a coin cell an MCU-based system must use the right components, careful analysis of energy needs and availability, and the proper algorithms in the firmware.

In this talk you’ll learn how to make these tradeoffs. And you may never trust a vendor promise again!

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Please log in or create an account to test your knowledge and see the answers.

What did Jack Ganssle identify as the primary practical reason claims of multi‑decade operation from a single coin cell are bogus?

A Because microcontroller vendors publish misleading 'typical' sleep current numbers, so you can't trust any published sleep numbers.

B Because the coin cell's vendor‑recommended shelf life and its increasing internal resistance limit usable capacity and the average current you can draw.

C Because printed circuit board leakage between traces is the dominant drain that kills coin‑cell life.

D Because decoupling capacitors inherently consume nearly all the battery capacity in any real design.

E Because using any LDO regulator will always draw enough quiescent current to prevent long life.

When waking a device briefly from a coin cell, what approach did Jack Ganssle recommend to avoid brownouts and crashes caused by the battery's internal resistance?

A Wake immediately at the MCU's maximum clock frequency so the work finishes fastest and you return to sleep sooner.

B Rely on a brownout reset circuit to catch voltage drops during the high‑current wake period.

C Come out of sleep at a low clock rate, measure battery voltage under load, then increase the clock rate only as much as the battery will support.

D Always use a linear LDO to isolate the MCU from battery voltage swings regardless of its quiescent current.

E Precharge a large capacitor so the MCU can always draw the transient current it needs without checking the battery.

What conclusion did Jack Ganssle reach about using large capacitors to provide millisecond‑scale current boosts from a coin cell?

A Using a large MLCC/X7R capacitor is a practical, low‑cost way to provide millisecond current bursts from a coin cell.

B Tantalum capacitors are ideal because their leakage is negligible and they reliably provide the needed burst energy.

C In practice the required capacitors are enormous, have problematic leakage and cost, and therefore the approach is impractical.

D Y5V dielectric capacitors are preferred because they give the highest capacitance and lowest leakage for burst support.

E A small cheap capacitor always solves transient needs without affecting the average battery budget.

According to Jack Ganssle, which factor most strongly determines long term battery life for ultra‑low‑power coin‑cell systems?

A Minimizing sleep current to nanoamp levels is the single most critical factor for achieving long life.

B The dominant factor is how much time the system spends awake and the current drawn while awake (duty cycle and awake current), not tiny differences in sleep current once sleep is very low.

C Printed circuit board surface leakage is typically the dominant determinant of battery life.

D Brownout reset circuitry is always negligible and can safely be ignored when budgeting power.

E Applying the P = C·V²·f equation directly to lower V is the most reliable way to predict battery life.

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Upvotes Newest Oldest

DS

Score: 0 | 3 years ago | no reply

I always enjoy hearing and reading what Jack has to say about the industry. While many of us just experience embedded design from within our own "trenches" working for a specific company, his perspective spans working with and consulting for many 100s of companies over this career. That vantage point allows him to see and recognize patterns that many of us never notice. Thank you for the presentation!

DanR

Score: 0 | 3 years ago | no reply

Thanks for sharing your perspective and wisdom!

Joffrey

Score: 0 | 3 years ago | no reply

Watched the recording. Really enoyed Jack's talk again with some helpful takeaways on low power designs.

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