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

11Hz

0

8

0

8

27Hz

1

16

1

32

3

12.5Hz

2

32

2

128

4

25Hz

3

64

3

512