Power Management in Microprocessor Application

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Power Management in Microprocessor Application

• Team 6
• Nilay Shah
• Justin Burr
• Brandon Holmes
• Ram Venkatachalam
• Bruce Frantz

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Benefits of Power Management Techniques

• Lower operating cost for device
• Longer battery usage time
• Constantly charging battery is a nuisance
• Selling point for portable devices
• Extend life of battery
• Ability to hold a charge diminishes over time

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Choosing Low Power Components

• Meet circuit design specifications
• Portable/wireless devices
• Cell phones, mp3 players, Gameboys, laptops,
  PDAs, etc.
• Produces heat

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Examples of Low Power Substitutes
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Power Management
Power Budgeting
Power Supply
Hardware
Software
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Power Budgeting
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Power Budgeting

• Predicting Current Consumption/Battery Life

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Calculating Battery Life
Average Current (mA) Total Charge (mA) /
(Total Time) 18.8E-6 (AmpSec) / 2000E-3
(Sec) 0.009 mA Peak Current 2.048 mA
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Design Factors for Power Supply

• 1. Voltage/Current Requirements
• 2. Battery Chemistry
• 3. Battery Performance
• 4. Battery Capacity
• 5. Battery Size/Weight
• 6. Battery Cost

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Choosing a battery

• High capacity batteries
• Primary vs. Secondary batteries
• Flat discharge voltage ex. NiMH
• Memory effect
• NiMH vs. NiCd
• Lithium Ion vs. NiMH

Discharge Rates for a Lithium-Ion cell
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Battery Performance

• The following shows the typical shelf life for
  some primary cells
• Zinc Carbon (Leclanché) 2 to 3 years
• Alkaline 5 years
• Lithium 10 years or more
• Typical self discharge rates for common
  rechargeable cells are as follows
• Lead Acid 4 to 6 per month
• Nickel Cadmium 15 to 20 per month
• Nickel Metal Hydride 30 per month
• Lithium 2 to 3 per month

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Battery Performance (contd)

• Li-ion
• Typically provides 300 500 charge/discharge
  cycles
• Exhibits permanent capacity loss as it ages
• Very light weight
• High energy-density
• Expensive
• Oxidation increases internal resistance
• NiMH
• 500 1000 charge/discharge cycles
• Exhibits slight memory-effect
• Capacity loss as battery ages is worse then Li-ion

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HARDWARE
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Power Management

• Switching Off External Circuits/Duty Cycle

Battery
Microcontroller
Sensor
Memory
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Power Management
Battery
Microcontroller
Sensor
Memory
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Clock Speed

• Power CV2f
• Slower clock speed
• Multiple clock speeds
• Idle/Sleep Modes

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Slower Clock Speed

• 10 different oscillator modes
• External crystal/resonator
• External RC network
• External clock
• Internal oscillator

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Multiple Clock Speeds

• Two-Speed start-up
• Dual clocks
• Switching clocks in software

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Idle/Sleep Modes
Run Mode
Idle Mode
Sleep Mode
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SOFTWARE
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Configuring Port Pins

• Unused Pins
• Output
• Unconnected
• Driven
• Input
• Pull up
• Analog Input
• Use if possible
• Low current drain

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I/O Initialization

• Configure each pin of each port
• Prevent glitches and unknown states
• Good design
• Easy software/hardware modification
• Prevents unpredictable outputs

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Software Optimization

• Avoid busy work
• Interrupts
• Pulse Width Modulation (PWM)
• Reduce external hardware

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Choosing a Microprocessor for Power Savings

• Low Voltage
• Low Frequency
• Internal Oscillator (if not time critical)
• Reduce Components
• PWM
• Internal pull ups
• A/D
• Idle or Sleep Mode
• nanoWatt Technology
• Idle - 5.8 µA at 2V 1MHz
• Sleep 0.1 µA at 2V 1MHz

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THANK YOU! ANY QUESTIONS/COMMENTS
?