E / 11815 / E

9/13

LDE Series

Digital low differential pressure sensors

www.first-sensor.com

www.sensortechnics.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):

p

e

t

Sl

a

m

i

c

e

d

a

x

e

Hy

r

a

n

i

Bn

o

i

t

p

i

r

c

s

e

D

1D

2

x

01

0

1

1

0

1

0

0

B

t

n

e

m

e

r

u

s

a

e

m

e

r

u

s

s

e

r

p

t

n

e

r

r

u

c

ll

o

P

24

1

x

00

0

1

0

1

0

0

0

Br

e

t

s

i

g

e

r

a

t

a

d

o

t

t

l

u

s

e

r

d

n

e

S

38

9

x

00

0

0

1

1

0

0

1

Br

e

t

s

i

g

e

r

a

t

a

d

d

a

e

R

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

factor

scale

counts

output

digital

Pa

pressure

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:

p

e

t

Sl

a

m

i

c

e

d

a

x

e

Hy

r

a

n

i

Bn

o

i

t

p

i

r

c

s

e

D

14

2

x

00

1

0

0

0

1

0

0

B

t

n

e

m

e

r

u

s

a

e

m

e

r

u

t

a

r

e

p

m

e

t

t

n

e

r

r

u

c

ll

o

P

24

1

x

00

0

1

0

1

0

0

0

Br

e

t

s

i

g

e

r

a

t

a

d

o

t

t

l

u

s

e

r

d

n

e

S

38

9

x

00

0

0

1

1

0

0

1

Br

e

t

s

i

g

e

r

a

t

a

d

d

a

e

R

From the digital sensor output, the actual temperature

can be calculated as follows:

temperature [°C] =

TS - TS

+ T

scale factor

where

TS is the actual sensor readout;

TS

Scale factor

SPI - SERIAL PERIPHERAL INTERFACE

Note: It is important 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

1

0

0

0

1

0

1

0

0

0

0

Step 2

Step 1

SCLK

(CPOL=0)

(CPHA=0)

MOSI

MISO

/CS

1

0

1

1

0

0

0

Data from sensor

Step 3

0

15 14 13 12 11 10

9

8

7

6

5

4

3

2

1

0

MSB

LSB