Power supply: consumption estimation and optimization
AN4450
12/26
DocID025978 Rev 1
3
Power supply: consumption estimation and
optimization
There are 2 supply voltages in the LPS25H: VDD and VDD_IO.
VDD is the core voltage used to supply to the internal circuits, power on reset, and the
sensor.
VDD_IO is the supply for the I
2
C / SPI blocks and interface signals.
In order to prevent possible leakage in the operational condition, it is necessary to ensure
VDD_IO <= VDD.
The operating voltage for both VDD_IO and VDD is 1.7 V to 3.6 V.
The LPS25H can also be powered directly by a small lithium coin battery like the CR2032.
This type of battery has a current capability of 220 mAh, enough to sustain the sensor peak
current (less than 1 mA).
Provided that the battery fluctuation, which could be in the range of 0.4 V, is within the
“normal operating voltage conditions” (even with an aged battery) and the recommended
decoupling capacitors are placed near the sensor, our tests with batteries and switched
resistive loads show that the sensor functions correctly even with fast slew rates.
During the main power-on transition, the system will initialize the internal registers according
to the factory-stored information (such as sensor calibration data).
This is triggered by VDD increasing above 1.6 V.
Current consumption during the device initialization peaks around 200 µA (for a duration of
about 600 µs).
After these steps, the LPS25H will enter a power-down state. The LPS25H is ready in
power-down from power-off in about 2.5 ms.
The LPS25H runs in normal mode from power-down state (toggling PD bit[7] in
CTRL_REG1, 0x20) in a few microseconds. Depending on register RES_CONF (0x10)
settings, the first valid measurement is ready after about 2 ms (minimum resolution, with
AVGT[1:0]=00; AVGP[1:0]=00, i.e. 8+8 samples) or about 37 ms (maximum resolution, with
AVGT[1:0]=11; AVGP[1:0]=11, i.e. 64+512 samples).
The typical conversion time (with +/-3% accuracy at room temperature) is given by the
formula:
Equation 1
Tconversion in µs = 62 * (Tavg + Pavg) + 975
where Tavg and Pavg are the values, respectively, for temperature and for pressure
measurements, selected in register RES_CONF as the number of averaged samples per
measurement.
–
Example: Tavg = 64; Pavg = 512; Typ. conversion time 36687 µs
The LPS25H has been designed to have a very low power consumption. The majority of the
internal blocks are switched-on only during the acquisition time. In one-shot mode the
device automatically goes into standby when the measurement is completed.
The minimum power consumption occurs when the device is in power-down (PD=0 bit[7] of
the CTRL_REG1 (0x20)) AND the interrupt pin is not configured to drain current. In normal
