User's Manual

UMXXX
6. Environmental MEMS sensors features
LPS22HH ACQUISITION CHAIN
The LPS22HH pressure sensor can perform a one-shot measurement and then return to
power-down mode, or it can operate in continuous mode with a programmable sampling
rate (1, 10, 25, 50, 75, 100 or 200Hz). The measurements can be taken in normal low-noise
mode, or in low-power mode to minimize current consumption. When continuous mode is
selected, low-noise mode is not available at 100 and 200Hz. In all cases, an optional low-
pass filter can be enabled with a programmable cutoff frequency to reduce the noise level
(the bandwidth is reduced from output data rate ODR/2 down to ODR/9 or ODR/20). The
low-pass filter is reset when it is enabled; after reset, a specific settling time is required
before the first correct sample on output (9 or 20 samples must be discarded, respectively).
Two programmable offsets can be subtracted from measured data:
• First, offset compensation (always): the offset measured with one-point calibration
(OPC) can be stored in specific registers (RPDS) and then subtracted from
subsequent measurements (OPC-compensated data = data – RPDS*256). The
low-pass filter, if enabled, will filter OPC-compensated data. Un/filtered OPC-
compensated data is stored in the FIFO.
• Second, auto-zero mode (optional): the offset-compensated (and possibly filtered)
pressure measurements is stored in specific registers (REF_P) when auto-zero is
enabled (AUTOZERO or AUTOREFP set to 1) and then it is subtracted from
subsequent measurements (AZ-compensated data = data – REF_P). Un/filtered
OPC-compensated data or AZ-compensated is stored in output registers.
LPS22HH INTERRUPT GENERATION AND FIFO BUFFER
The LPS22HH pressure sensor can be configured to generate interrupt events related to
pressure acquisitions (see below) and FIFO status (watermark reached, full, overrun).
The interrupt can be generated when a new pressure or temperature sample is available;
or when the AZ-compensated data exceeds a programmed threshold (THS_P) in the
positive (PHE flag enables the comparison with +THS_P) or negative direction (PLE flag
enables the comparison with –THS_P). There are three configurations:
• AUTOZERO=0 and AUTOREFP=0: interrupt logic is disabled; un/filtered OPC-
compensated data goes to FIFO and output registers.
• AUTOZERO=1: interrupt logic is enabled; REF_P is set when interrupt is enabled;
AZ-compensated data goes to the interrupt logic and to the output registers, while
un/filtered OPC-compensated data goes to FIFO.
• AUTOREFP=1: interrupt logic is enabled; REF_P is set when interrupt is enabled;