User's Manual

UMXXX
to enable the lowest power consumption in sleep mode:
• Sleep mode, 32kHz RO (Ring oscillator), 24kB RAM retention: 2.1uA at 3V
• Sleep mode, 32kHz XO (Crystal oscillator), 24kB RAM retention: 0.9uA at 3V
RADIO FREQUENCY SECTION
The Radio Frequency section of the BLE sensor node includes three elements:
• The first element is BALF-NRG-02D3, an ultra-miniature balun which integrates
matching network and harmonics filter.
• The second element is a Π-network which provides the flexibility to get additional
filtering and also provides access points for testing. This network is not populated
as the integrated balun provides the necessary matching.
• The third element is the SMD 2.4GHz antenna which needs a specific clearance
area on the PCB and specific passives for perfect tuning (FT1, FT2 and MT).
MEMS SENSOR SECTION
The Sensor section of the BLE sensor node includes inertial and environmental MEMS
sensors connected to BlueNRG-2 by means of an I2C bus operated at 400kHz.
The MEMS microphone is connected to BlueNRG-2 using a dedicated line to transfer the
PDM (Pulse Density Modulated) stream at 1.6MHz. The PDM stream is converted to PCM
(Pulse Coded Modulation) by the integrated digital filter included in the ADC block on
BlueNRG-2.
All sensors can generate interrupts, but in the BLE sensor node, only two interrupt pins are
connected to BlueNRG-2 using dedicated and independent lines: the interrupt from the
LIS2MDL magnetometer and the interrupt from the LSM6DSO accelerometer and
gyroscope.
• The LIS2MDL magnetometer interrupt line is only push-pull and must have its own
independent line. The interrupt pin of this sensor is connected to BlueNRG-2 to
enable applications such as “reed-switch” (switch activated by an external magnet).
• The LSM6DSO smart accelerometer and gyroscope interrupt pin is an input at boot.
It has an internal pull-down. If the pin is low at boot, the I2C interface is selected,
otherwise the I3C interface is selected. The pin can be reconfigured as open-drain
but the external pull-up would cause an additional power consumption. The
interrupt pin of this sensor is connected to BlueNRG-2 to fully exploit the “smart”
embedded processing (single/double tap recognition, free-fall, wakeup,
portrait/landscape, 6D/4D orientation detection; activity/inactivity, stationary/motion