EA-APP-002 Embedded Artists, EA-APP-002 Datasheet - Page 29

• 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
5.3.6
The accelerometer can be placed in a sleep mode where the current consumption is 0.1uA maximum.
Read the datasheet for the accelerometer to get information about active mode and associated current
consumption. There are different sample rates that can be programmed and resulting in different
current consumption.
5.3.7
The capacitive sensor can be placed in a sleep mode where the current consumption is 0.1uA
maximum. The current consumption in active mode is around 10uA. Read the datasheet for details.
5.3.8
There is no voltage supervisor/reset generator on the board. The LPC11U37 has functionality for this.
Note however that when enabling the Brown Out Detector (BOD) correct consumption of the
LPC11U37 will increase with about 50uA. This is far more than the 2uA consumption on power down
mode.
5.4 How to Measure Current Consumption
There are 5 ohm resistors on the board for measuring the current consumption at three places:
With a 5 ohm resistor, every 10 mV equals 2mA of current consumption. The value 5 ohm is a trade-off
between measurement resolution and minimizing voltage drop. The maximum current consumption of
the board is about 17 mA, with result in a voltage drop of 85mV. That is an acceptable voltage drop
that will not affect the operation of the board.
The 5 ohm resistor is useful for measuring current consumption on the mA-region when using a normal
low-cost portable multimeter. It will however not work for measuring currents in the uA-region.
If the application switches between many different operating modes with different current consumption,
it can be difficult to measure the real consumption with a cheap multimeter. A more advanced voltage
meter might be required. For fast events and changes, an oscilloscope can with advantage be used to
measure the current consumption.
It is possible to replace the 5 ohm resistors but this shall be done with caution. The LPC11U37 will
have high current consumption during startup and ISP/bootload mode. Make sure the jumpers in JP1
and JP3 short the measuring resistors during for example flashing of the LPC11U37. When the
operating mode of interest has been reached the jumpers can be removed and the voltage drop can be
measured. If the application changes between current consumption modes, it can be impossible to get
it working properly (if the highest current consumption will cause too high voltage drop over the
measuring resistor).
5.4.1
2.5uA will generate a 7.5uV voltage drop over a 5 ohm resistor. This is too small to measure reliable
without a very high precision (and high cost) voltage meter. A solution is to replace R34 with a 5K ohm
1) R34 (see schematic page 6) which is placed just after the 3.0V voltage regulator. It is possible
2) R13 (see schematic page 2) which is connected to the VDDCORE pin of the LPC11U37. It is
3) R11 (see schematic page 2) which is connected to the VDDIO pin of the LPC11U37. It is
to measure the total current consumption of the board with this resistor.
possible to measure the current consumption of the LPC11U37 core with this resistor.
possible to measure the current consumption of the IO pins of the LPC11U37 with this
resistor.
Accelerometer Sensor
Capacitive Sensor
LPC11U37 Brown Out Detector
How to Achieve and Measure 2.5uA Current Consumption
a. Most LPC11U37 pins have a (programmable) pull-up resistor. It is possible to
measure the current consumption from each of these resistors. Each enabled
resistor draws about 40uA if the pin is held low.
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