DocID025978 Rev 1
13/26
AN4450
Power supply: consumption estimation and optimization
26
operating mode the power consumption depends on HW-averaging (resolution) and output
data rate (auto-refresh frequency) settings. The following formula gives an indication of the
current consumption in relation to average and ODR. This can be used to find the best
compromise, for a given application, between consumption, update speed and filtering.
Equation 2
Idd = [(3uA/Hz +42nA/Hz*Pavg) + 30nA/Hz*Tavg]*ODR
where:
Pavg = value set by AVGP[1:0] (8, 32, 128, 512)
Tavg = value set by AVGT[1:0] (8,16, 32, 64)
ODR = rates according to ODR[2:0] (1, 7, 12.5, 25Hz)
a) Example
1:
–
ODR= 25 Hz
–
Pavg= pressure average=512
–
Tavg= temperature average=64
–
Idd= 661 µA (Vdd independent at first approximation)
b) Example
2:
–
ODR=1 Hz
–
Pavg= pressure average=512
–
Tavg= temperature average=64
–
Idd= 26.4 µA
c) Example
3:
–
ODR= 1 Hz
–
Pavg= pressure average=8
–
Tavg= temperature average=8
–
Idd= 3.6 µA
In order to improve system power saving, the LPS25H embeds a FIFO buffer capable of
storing up to 32 pressure output values. Since the host processor does not need to
continuously poll data from the sensor, it can wake up (on programmable interrupt from the
sensor) only when requested and burst the significant data out from the buffer.
The FIFO can alternatively be configured as moving average to reduce the noise figure (or
to reduce the ODR rate while keeping the same noise figure, traded for delay).
Table 2. ODR, AVGT and AVGP correspondence
ODR[6..4]@0x20
ODR
AVGT[3..2]@0x10
Tavg
AVGP[1..0]@0 x10
Pavg
1
1Hz
0
8
0
8
2
7Hz
1
16
1
32
3
12.5Hz
2
32
2
128
4
25Hz
3
64
3
512
