XLP nanoWatt Microcontrollers

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XLP nanoWatt Microcontrollers

• Low Power Management

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Industry Trend

• Many types of portable electronics
• Metering applications
• Medical devices
• Power consumption becomes one of the most
  important concerns for designers

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Power Consumption

• Dynamic
• Power used by the switching of the digital logic
• Voltage and temperature impact power usage in a
  small way
• Mainly influenced by clock speed
• Static
• Power consumption when clock is disabled
• Transistor leakage currents
• Power used by voltage supervisors and other
  circuits needed to resume normal operation from
  static mode
• Higher impact from voltage and temperature

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Power Saving Modes

• Deep sleep mode
• The lowest of the static power modes
• Except a few RAM locations, the wake-up circuitry
  and in some cases a low power oscillator used for
  RTCC, everything is powered down
• Wake-up resets the device, and the firmware has
  to check special registers to resume normal
  operation state
• Used when long sleep times and very long battery
  life are required
• Accurate timekeeping is possible
• No peripherals may run during deep sleep
• Typical power consumption is less than 50nA

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Power Saving Modes

• Sleep mode
• Standard low power mode that predates nanoWatt
  technology
• Core and most peripheral clocks are shut down
• General purpose RAM, registers and Program
  Counter are preserved
• Wake-up times are very short, with little
  firmware overhead
• Used when shorter sleep times and very short
  wake-up times are required.
• ADC (with own RC oscillator) and comparators may
  be used during sleep
• Typical power consumption is between 50-100nA

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Power Saving Modes

• Idle mode
• Dynamic reduction mode intended to allow for
  greater peripheral functionality than the static
  modes
• Core clock is removed while still provided to the
  peripherals
• On some devices it is possible to apply the
  system clock only to selected peripherals
• Idle mode consumes significantly more power than
  any of the static modes
• Useful in cases in which high speed ADC,
  time-critical communications or DMA transfers are
  needed
• It may significantly reduce power usage when the
  device is waiting for data transfers, timer
  overflows and output compare events
• Typical current consumption around 25 of normal
  run mode

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Power Saving Modes

• Doze mode
• Dynamic reduction mode allowing full peripheral
  and some core functionality
• System clock is applied to peripherals
• A user defined fraction of this clock is still
  applied to the core
• Similar to IDLE mode, but core continues to run
  at reduced speed
• Power consumption up to 75 of normal run mode
  depending on application

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Clock Switching

• IDLE and DOZE modes allow reduction of core power
  consumption while peripherals are still clocked
  at full speed
• Clock switching allows reducing the speed of
  clocks for the entire device
• The system clock source may be selected depending
  upon the situation
• Slower crystals or internal RC clocks may be used
  in code sections that are not time critical
• Computation intensive code or time critical
  sections may conveniently switch back to a high
  speed clock source

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Application Examples

• Methane gas / smoke sensor
• Device enters deep sleep and wakes up every
  second to sample sensor data
• If data over threshold device switches to
  standard sleep mode and samples sensor data 10
  times faster to confirm readings
• Alarm is raised after confirmation
• Device reverts to normal operation

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Application Examples

• Normal consumption _at_ 4MIPS is 4mA
• Current consumption in sleep mode with 32kHz
  watch crystal running on TIMER1 is 500nA100nA
  static
• Acquiring 8 ADC samples and deciding if values
  over threshold takes less than 500us
• Duty cycle estimated to 0.05 (500us out of 1s)
• Average current consumption is 4000uA0.050.6uA
  99.952.5997uA
• Excluding leakage, device may run 22 years using
  a pair of 500mAh AAA batteries

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Thank you!