E / 11815 / D 9/13
LDE Series
Digital low differential pressure sensors
www.first-sensor.com
Data read – pressure
When powered on, the sensor begins to continuously
measure pressure. To initiate data transfer from the
sensor, the following three unique bytes must be written
sequentially , MSB first, to the MOSI pin (see Figure 5):
petSlamicedaxeHyraniBnoitpircseD
1D2x010110100B
nemerusaemerusserptnerruclloP
241x000101000BretsigeratadottluserdneS
389x000011001BretsigerataddaeR
The entire 16 bit content of the LDE register is then
read out on the MISO pin, MSB first, by applying 16
successive clock pulses to SCLK with /CS asserted
low . Note that the value of the LSB is held at zero for
internal signal processing purposes. This is below the
noise threshold of the sensor and thus its fixed value
does not affect sensor performance and accuracy .
From the digital sensor output the actual pressure
value can be calculated as follows:
[] []
=
Pa
counts
factorscale
countsoutputdigital
Pa
ressure
Fig. 5: SPI data transfer
For example, for a ±250 Pa sensor (LDES250B...)
with a scale factor of 120 a digital output of 30 000
counts (7530’h) calculates to a positive pressure of
250 Pa. Similarly, a digital output of -30 000 counts
(8AD0’h) calculates to a negative pressure of -250 Pa.
Data read – temperature
The on-chip temperature sensor changes 95 counts/°C
over the operating range. The temperature data format
is 15-bit plus sign in two’s complement format. To
read temperature, use the following sequence:
petSlamicedaxeHyraniBnoitpircseD
10x2AB00101010
emerusaemerutarepmettnerruclloP
241x000101000BretsigeratadottluserdneS
389x000011001BretsigerataddaeR
From the digital sensor output, the actual temperature
can be calculated as follows:
temperature [°C] = TS - TS0 [counts] + T0 [°C]
scale factorTS[counts/°C]
where
TS is the actual sensor readout;
TS0 is the sensor readout at known temperature T014;
Scale factorTS = 95 counts/°C
SPI - SERIAL PERIPHERAL INTERFACE
Note: It is import ant to adhere to the communication protocol in order to avoid damage to the sensor.
SCLK
(CPOL=0)
(CPHA=0)
MOSI
MISO
/CS
0 1 0 1 1 10 0 0 1 0 1 0 000
Step 2Step 1
SCLK
(CPOL=0)
(CPHA=0)
MOSI
MISO
/CS
1 0 1 1 000
Data from s e nso rStep 3
0
15 14 13 12 11 10 9876543210
MSB LSB