1. Getting the Most Out of Low Power MCUs
Part I: Low Power MCU Concepts and Capabilities
1/14/2013
Warren Miller

2. This Week’s Agenda
1/14/13 Low Power MCU Concepts and Capabilities 1/15/13 Low Power Modes in Detail 1/16/13 Low Power Peripherals 1/17/13 Extending Battery Lifetime 1/18/13 Advanced Example Designs

3. This Week’s Agenda
1/14/13 Low Power MCU Concepts and Capabilities 1/15/13 Low Power Modes in Detail 1/16/13 Low Power Peripherals 1/17/13 Extending Battery Lifetime 1/18/13 Advanced Example Designs

4. Class Description
Modern MCUs have a variety of features that support very low power operation.
In order to get the most out of these new devices we will review common concepts
Like special low power operating modes
and common capabilities
Like special peripheral operations
that most modern Low Power MCUs share.

5. Today’s Topics Goals and Objectives Why Low Power?
MCU Power- an Overview
Power Sources, Voltage Characteristics, Current Characteristics
Processing Efficiency
MCU Architecture- an Overview
Processor
Memory
Peripherals
Common Low Power MCU Capabilities
Low Frequency Operation, Low Operating Voltage
Low Power Modes, Low Power Peripherals

6. Goals and Objectives
Understand, at the overview level, key concepts we will use in the rest of the class
Power Sources
Main MCU elements and any special low power characteristics (CPU, Memory and Peripherals)
Low Frequency Operation
Low Voltage Operation
Low Power Modes

7. Why Low Power?
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)

8. MCU Power- An Overview Power Sources: Battery Energy Harvesting
Size, mAh, Self Discharge, Lifetime
Energy Harvesting
Solar, Thermal, Pressure, Magnetic, etc
Super Cap
Voltage, Charge (Current over time)
System Power
Why would low power be important?
Mains
200mAh
2000mAh

9. MCU Power- An Overview 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

10. MCU Active Characteristics MCU Efficiency Metrics (DMIPS-based)
MCU Power- An Overview
Processing Efficiency
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…

11. MCU Architecture- CPU CPU Blocks Program Counter Instruction Register
Control Unit
Register File
ALU
Status Register
Stack Pointer
Some Low Power Points: Data Processing Width, Number of Working Registers vs State Save Time and Active Power Requirements

12. MCU Architecture- CPU Control
Inst #1
Inst #2
Inst #3
Inst #4
Fetch
Decode
Execute
Pipelined Execution
Fetch, Decode, Execute
Sequential Operations
Pipeline Stall
Intelligent Control- Low Power
Disable Decode Blocks
Separate Execution Units
Gated Clocks

13. MCU Architecture- Memory
Low Power Features
Code Memory: Flash
Fetch size
Wait states
Cache
Data Memory: SRAM
Volatile
Battery back-up
Execute program from RAM

14. MCU Architecture- Memory
Low Power Features
Data Flash
Non-volatile
Key Configuration Data
Saved Operating Data
Resets or Brown-out
Tamper Protection
Time Stamps
Power Failure Data

15. MCU Architecture- Peripherals
GPIO
GP Timer
Low Power Features
Bus Interface
Peripheral Functions
GPIOs
Serial Standards
Independent Operation
GP Timers
Watchdog Timers
Interrupts
DMA
Interrupt
DMA
Serial
CPU
Debug
Mult
Div
MAC
Clock
Watch Dog

16. MCU Architecture- Peripherals
Low Power Features
Clock Frequency Requirements, Analog to Digital Conversion
Battery Back-up, Low Voltage Detection

17. MCU Low Modes- Overview
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.
Much more in next class.

18. 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.

19. Additional Resources
WE Energy Harvesting Brochure: MicroChip XLP Technology: STMicroelectronics STM32L: Energy Micro MCUs: TI MSP430 MCUs: Renesas RL78 MCUs: Renesas RL78 Eval Kit:

20. This Week’s Agenda
Tomorrow
1/14/13 Low Power MCU Concepts and Capabilities 1/15/13 Low Power Modes in Detail 1/16/13 Low Power Peripherals 1/17/13 Extending Battery Lifetime 1/18/13 Advanced Example Designs