MPL3115A2

Sensors

16

Freescale Semiconductor, Inc.

6.1

Factory Calibration

The device is factory calibrated for sensitivity, offset for both Temperature and Pressure measurements. Trim values are

stored, on-chip, in Non-Volatile Memory (NVM). In normal use, further calibration is not necessary; however, in order to realize

the highest possible accuracy, the device allows the user to override the factory set offset values after power-up. The user ad-

justments are stored in volatile registers. The factory calibration values are not affected, and are always used by default on power-

up.

6.2

Barometer/Altimeter Function

The mode of operation of the device can be selected as Barometer or Altimeter. The internal sensor gives an absolute pressure

signal. The absolute pressure signal is processed to provide a scaled pressure or an altitude, depending on the mode selected.

The combination of a high performance sensor and the signal processing enable resolution of pressures below 1 Pa and altitude

resolution of better than 1 Ft / 0.3m at sea level.

When in Barometer mode, all pressure related data is reported as 20-bit unsigned data in Pascals. When in Altimeter mode,

all pressure data is converted to equivalent altitude, based on the US standard atmosphere and then stored as 20-bit 2’s com-

plement value in meters and fractions of a meter.

6.2.1

Barometric Input

In order to accurately determine the altitude by pressure, a facility is provided to input the local barometric pressure correction.

The default value is 101,326 Pa since the register is in units of 2 Pascals per LSB.

6.3

Temperature Function

The unit contains a high resolution temperature sensor that provides data to the user via a 16-bit data register, as well as for

internal compensation of the pressure sensor.

6.4

Autonomous Data Acquisition

The unit can be programmed to periodically capture Altitude/Pressure and Temperature data. Up to 32 data acquisitions can

be stored in the internal FIFO. The interval between acquisitions is programmable from 1 second to 9 hours.

Data: (Up to 32 samples over 12 days). The unit can also be programmed to make a single reading and then go to standby

mode.

6.5

FIFO

A 32 sample FIFO is incorporated to minimize the overhead of collecting multiple data samples. The FIFO stores both Tem-

perature and Pressure/Altitude data. The device can be programmed to autonomously collect data at programmed intervals and

store the data in the FIFO. FIFO interrupts can be triggered by watermark full or data contention (FIFO GATE) events.

6.6

External Interrupts

Two independent interrupt out pins are provided. The configuration of the pins are programmable (polarity, open drain or push-

pull.) Any one of the internal interrupt sources can be routed to either pin.

6.6.1

Reach Target Threshold Pressure/Altitude (SRC_PTH)

The interrupt flag is set on reaching the value stored in the Pressure/Altitude target register. Additionally, a window value pro-

vides the ability to signal when the target is nearing from either above or below the value in the Pressure/Altitude target register.

When in barometer mode, these values represent pressures rather than altitudes.

Examples:

• Set Altitude alert to 3000m and window value to 100m, interrupt is asserted passing 2900m, 3000m, and 3100m.

• Set Pressure alert to 100.0 kPa and window value to 5 kPa, interrupt can be sent passing 95 kPa, 100 kPa and 105 kPa.

Note: When the window value is set to 0 then the interrupt will only be generated when reaching or crossing the target value.

6.6.2

Reach Window Target Pressure/Altitude (SRC_PW)

The interrupt flag is set when the pressure/altitude value is within the window defined by the following formula:

Note: No interrupt is generated if the P_WND value is set to 0.

Window

P_TGT

MSB LSB

,

P_WND

MSB LSB

,

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=