User manual

Low-power Application Kit (Oryx) - User’s Guide
Page 12
Copyright 2012 © Embedded Artists AB
PIO1_31
Not used, free for expansion
Pin 52
USB-DM
USB interface
Pin 36
USB-DP
USB interface
Pin 37
3.4 Schematic Walkthrough
3.4.1 Page 2
The center of the board is the LPC11U37 from NXP. It is a MCU based on the ARM Cortex-M0 core.
LPC11U37 has many power modes to save power consumption. See datasheet for details. It is
possible to measure the current consumption of the LPC11U37 on both VDD pins separately (IO and
VDDCORE). Normally both jumpers in JP1 are inserted but if removed there are 5 ohm resistors that
can be used for measuring the current consumption. 10mA current will give a 50mV voltage drop over
a 5 ohm resistor.
J1 is the SWD interface for LPC11U37, i.e., debug interface. It is the new and smaller footprint
standard ARM debug connector. It has 2x5 pins in 50 mil pitch.
The LPC11U37 has a USB Device interface. The interface is very straight forward and consists of a
mini-B USB connector (J2), ESD protection, VBUS sense and DP pull-up resistor control.
SW1 is a reset push-button. There is no external voltage supervisor since the LPC11U37 has its own
power-on reset functionality.
SW2 is a wake-up push button for waking the LPC11U37 from ‘deep power down mode’. SW2 is
connected to PIO0_16, which is the WAKEUP pin. A high-to-low transition on this pin will wake-up the
LPC11U37 from ‘deep power down mode’. PIO0_16 is the only pin that can wake-up the LPC11U37
from this mode.
SW3 is an ‘ISP enable’ push-button. By pressing SW3 while resetting the LPC11U37 (pressing and
releasing SW1) the In-System Programming mode is entered. It is an internal boot loader more of the
LPC11U37. It can be useful to enter ISP mode if the application program has programmed the internal
PLL:s wrong, or disabled the debug/SWD interface. In these situations, it can be impossible to get
contact with the LPC11U37 via the debug/SWD interface. The application program can be erased
while in ISP mode and a new, correct application program can be downloaded.
R22 is a 100K trimming potentiometer for simulating an arbitrary analog input signal. There is a power
switch to keep current consumption low. PIO1_13 controls Q3 (P-channel mosfet). When enabled, the
current consumption is 30 uA (= 90 uW). Supply voltage is only needed during an ADC conversion so
the mean current consumption can be kept very low. R22 is connected to analog input 7 (AD7),
PIO0_23.
J3 can be used to signal power consumption digitally. The connector carries 7 pins from the
LPC11U37 that can be used to signal different power states. A logic analyzer can be used to capture
and analyze the different states (and their length) that the application program changes between.
3.4.2 Page 3
There are many I2C peripherals on the board. Three of them are on page 3 of the schematic. All three
chips are constantly powered since they can be put in low-power modes where they consume very low
power. There is an optional power control on the two i2c pull-up resistors. Currently there is no use for
this feature since disabling the pull-up resistors will not reduce the power consumption. PIO1_23 shall
typically always be pulled low (which will enable the pull-up resistors), or R18 shall be mounted It is not
possible to communicate over the i2c-bus without having the pull-up resistors enabled.
The ADXL345 3-axis accelerometer is from Analog Devices. The ADXL345 has functionality to detect
single and double taps (on the board pcb). The chip has two interrupt outputs that can be used to
wake-up the LPC11U37 from a power down mode, for example when a user double-tap on the board.