1. Class 1: An Introduction to Low Power Systems
Designing Low Power Systems using Battery and Energy Harvesting Energy Sources
Class 1: An Introduction to Low Power Systems
May 4th, 2015 Warren Miller

2. Course Description
Low power systems are all around us and use is exploding- IoT, wearable devices, handheld, energy harvesting, etc Understanding how to implement low power systems, from batteries or energy harvesting, will be a key skill for engineers in these growing markets. This course will provide sufficient background to get you familiar with the key concepts, techniques and devices needed for the next generation of low power systems.
Low power systems are all around us and with the explosion of new applications for the Internet of Things and wearable devices low power systems will become even more common. Understanding how to implement low power systems, either from batteries or using energy harvesting techniques, will be a key skill for engineers in these growing markets. This course will provide sufficient background to get you familiar with the key concepts, techniques and devices needed for the next generation of low power systems.

3. This Week’s Agenda
5/4/15 An Introduction to Low Power Systems 5/5/15 Battery Power for MCUs and FPGAs 5/6/15 Energy Harvesting 5/7/15 Low Power MCUs and FPGAs 5/8/15 Example Designs

4. Today’s Class Goals and Objectives Why is Low Power Important?
Power Sources
Energy Harvesting
Using MCUs and FPGAs as Low Power Controllers
Processing Efficiency
Battery Operation Considerations
References
Understand, at the overview level, key concepts we will use in the rest of the class
Power Sources
MCUs and FPGAs as Low Power Controllers
Energy Harvesting

5. Today’s Goals and Objectives
Understand, at the overview level, key concepts we will use in the rest of the class
Power Sources
MCUs and FPGAs as Low Power Controllers
Energy Harvesting

6. Why is Low Power Important?
More than $9B in products using rechargeable batteries used in homes, retail and warehouses
Battery powered electronics use over $30B in electricity annually
5-10% of residential electricity cost comes from standby power (equipment on, but not doing anything)

7. Power Sources Battery Super Cap System Power Mains
Size, mAh, Self Discharge, Lifetime
Super Cap
Voltage, Charge [I x t = C x (V0 – V1)]
System Power
Why would low power be important?
Mains
2000mAh
200mAh
Linear Tech SuperCap Charger

8. Energy Harvesting Solar (Photovoltaic) Thermal (TEG)
2W peak for a 160cm2 surface area
Thermal (TEG)
Thermal to Electrical or Visa Versa
Pressure/Vibration (Piezoelectric)
5mW for .1 in displacement at 75Hz 16 grams
Air/Fluid Flow
Fans in reverse!

9. Using MCUs and FPGAs as Low Power Controllers
Why MCUs?
Low Power Characteristics
Software Programmable
Inexpensive
Easy to Design (Simple)
Why FPGAs?
Software and Hardware Programmable
Efficiency, Small Footprint (Integration)
Getting Easier to Design With

10. MCU Power Considerations
Voltage and Current Characteristics
Voltage Range
Wide range of VCC for battery operation
Internal regulator to generate core voltage
Voltage vs. Frequency
Higher frequency of operation requires higher voltage, PLL, Clock Osc, Flash Memory, Logic
Static Current
The amount of current required when nothing is switching
Dynamic Current
When signals switch state, current flow is required

11. FPGA Power Considerations
FPGA Power Requirements
Number of power rails
Power supply ramp and timing
Inrush current (Max vs. Normal)
Power management for power fluctuations
FPGA Current Sources
Static Current
SRAM Cells, PLLs, SERDES, Hardened Blocks
IOs, On-chip Memories, Programming/Configuration
Dynamic Current
Clocks, PLLs, Internal Signals, IOs
Hardened Blocks, Global Signals, SERDES
FPGA Power Savings
Technology, Capacity, Vcc, Power Domains, Sleep Modes

12. Processing Efficiency- MCUs
Max Clock Rate
Instruction Cycle Time
Wait States mA
mA/DMIP
Other Considerations
Power Consumption
MCU #1
MCU #2
MCU #3
MCU Active Characteristics
MHz
100
168 mA 35 87 66
mA/MHz
0.35
0.52
0.66
MCU Efficiency Metrics (DMIPS-based)
DMIPS
165
125
mA/DMIPs
0.21
0.70
0.53
DMIPS = Drystone MIPS, a benchmark for integer based processing. A mix of common processing functions used to compare various computer architectures. 20 years old so it is still useful but should not be considered the only metric needed. Pun on Whetstone which included Floating Point operations. Note: DE Vax 11/780 is considered a 1 MIPS machine with 1757 Drystones per second. DMIPS can result in better measures for CISC architectures vs RISC architectures if the CISC machine can process DMIPS functions in fewer instructions…

13. Low Power Modes- MCU Modes Run: CPU, Clock, Peripherals: Running
Sleep, Wait: CPU Clk Gated; Clock, Peripherals: Running
Stop: CPU, Some Peripherals, Some Clocks: Gated
Standby, Hibernate: CPU, Clock: Off; Some Peripherals: External Clock
Other Blocks
Flash, SRAM, Regulator, PLL, Osc, etc.
RTC, WDT, Brownout Detect, etc.
Additions
Very Low Power, Deep, Snooze, etc.
Different names for similar functions. You need to read the detailed descriptions in suppliers datasheets.

14. Specialized Low Power Peripherals
Low Power Oscillators
Low Power Interval Timers
Low Power Watchdog Timers
Battery Back-up Operation
Input Detection
Low Power UART
Etc.

15. Processing Efficiency- FPGAs
Different Approach
Clock Rate
Variable
Pipeline for Efficiency
Latency is your friend
Serial/Parallel for Efficiency
Very flexible!
On-chip Memory
For buffering and overlap
Be Creative!

16. Battery Operation Considerations
Battery Back-up
Keep a portion of the MCU active
Wake-up Circuitry!
Battery Operation
Voltage droop, What to do?
Fall back plan
Battery Charging
Battery Replacement

17. Additional Resources
Microchip XLP Technology ST Micro Ultra Low Power MCUs Silicon Labs Battery Operated MCUs TI Ultra Low Power MCUs RL78 MCUs Renesas RL78 Low Power Evaluation Kit Lattice iCE40 Ultra FPGAs Microsemi IGLOO2 FPGAs WE Energy Harvesting Brochure WE Reference Solution Kits CEC Course- Low Power MCUs

18. This Week’s Agenda
5/4/15 An Introduction to Low Power Systems 5/5/15 Battery Power for MCUs and FPGAs 5/6/15 Energy Harvesting 5/7/15 Low Power MCUs and FPGAs 5/8/15 Example Designs