EA-APP-002 Embedded Artists, EA-APP-002 Datasheet - Page 25

• Manufacturer Part Number: EA-APP-002
• Description: Development Boards & Kits - ARM LOW POWER APP KIT LPC11U37 (ORYX)
• Manufacturer: Embedded Artists

Specifications of EA-APP-002

• Rohs: yes
• Product: Demonstration Kits
• Tool Is For Evaluation Of: LPC11U37
• Core: ARM Cortex M0
• Interface Type: I2C, USB
• Operating Supply Voltage: 5 V

Copyright 2012 © Embedded Artists AB
Low-power Application Kit (Oryx) - User’s Guide
5 Software Techniques for Low-power Design
This chapter will discuss low-power design techniques. Part of the discussion is general for all low-
power designs and part is specific for the board design.
Low-power design has two main principles:
Hardware and software must work together, hand-in-hand to achieve a low-power design. Active time
(periods of high current consumption) must be reduced as much as possible. If time of inactivity is
much longer than active periods, then the current consumption of the low-power mode is more
important to reduce. The time of low-power consumption can be called sleep mode as a general term.
An illustrative example; assume a device that wakes up for 100mS once every 100 seconds. Whatever
the power consumption is during the active period it will only affect the total power consumption by
0.1%. 99.9% origin from the sleep power consumption.
Assume active current is 150mA and sleep current is 20uA. The mean current consumption then
becomes 170uA. The active current is clearly dominating consumption in this case.
If the active current is instead 15mA and sleep current is still 20uA. Further assume that the active
period is reduced to 50mS (instead of 100mS). In this case, the mean current consumption becomes
27.5uA. Now the current consumption is dominated by the sleep current.
The active current of the board running at full speed is about 15mA (can be up to 20mA if everything is
active simultaneous). The lowest power consumption is about 2.5uA. The temporal structure of an
application will give where in between these extremes the mean power consumption will be. At full
power consumption the Lithium battery will last for about 3 hours. At 2.5uA it will last for 18000 hours.
This is about 2 years. Note that at this long time scale the self-discharge of the rechargeable Lithium
battery becomes an issue. That is however out of scope for this discussion.
5.1 LPC11U37 Operating Modes
The LPC11U37 has a number of different operation modes. The modes are described in detail in the
LPC11U37 UM (Users Manual), a section called Power management. An application can switch
between the different modes to achieve lowest possible power consumption. Below is a short
description of the modes. Consult the LPC11U37 UM for details.
1. Design the hardware to be able to control the current consumption by enabling/disabling
2. Design the software to be able to control the active parts of the hardware as much as
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different parts of the hardware. The parts that are active most of the time shall have as low
static current consumption as possible.
possible. In between active periods, the software shall put the hardware to lowest possible
current consumption.
Active – in this mode the processor core is running and executing the application. Power
consumption can be optimized by adjusting power and clock frequencies to selected
peripherals. There are also Power Profiles that can set.
Sleep – in this mode the core clock is stopped and execution of instructions is suspended
until either a reset or an interrupt occurs. Before entering sleep mode it is possible to set
which peripheral functions to be active during the sleep. An interrupt from an active peripheral
can generate an interrupt and cause the processor to resume execution.
Deep sleep – this mode is more fixed than sleep mode. More peripherals are shut down to
conserve more power.
Power down – this mode is even more fixed. More functionality is shut down to conserve
power.
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