MS5540C Miniature Barome ter Module
DA5540C_008 www.meas-spec.com March 25, 2014
0005540C1193 ECN2224 1/20
• 10 - 1100 mbar absolute pressure range
• 6 coeffi cients for software compensation stored on-chip
• Piezoresistive silicon micromachined sensor
• Integrated miniature pressure sensor 6.2 x 6.4 mm
• 16 Bit ADC
• 3-wire serial interface
• 1 system clock line (32.768 kHz)
• Low voltage and low power consumption
DESCRIPTION
The MS5540C is a SMD-hybrid device including a precision piezoresistive pressure sensor and an ADC-
Interface IC. It is a miniature version of the MS5534C barometer/altimeter module and provides a 16 Bit data
word from a pressure and temperature dependent voltage. MS5540C is a low power, low voltage device with
automatic power down (ON/OFF) switching. A 3-wire interface is used for all communications with a micro-
controller.
Compared to MS5534A the pressure range (measurement down to 10 mbar) has been improved. The MS5540C
is fully software compatible to the MS5534C and previous versions of MS5540. In addition, the MS5540C is from
its outer dimensions compatible to the MS54XX series of pressure sensors. Compared to the previous version
the ESD sens it ivity level has been improved to 4k V on all pins . T he gel pr ot ec tion of the sensor pr ovides a water
protection sufficient for 100 m waterproof watches without any additional protection.
FEATURES APPLICATIONS
•
Resolution 0.1 mbar
•
Mobile altimeter / barometer systems
•
Supply voltage 2.2 V to 3.6 V
•
Weather control systems
•
Low supply current < 5 µA
•
Adventure or multi-mode watches
•
Standby current < 0.1 µA
•
GPS receivers
• -40°C to +85°C operation temperature
•
No external components required
BLOCK DIAGRAM
VDD
GND
MCLK
SCLK
DOUT
Input MUX
ADC
Digital
Interface
Memory
(PROM)
64 bits
SENSOR
SGND
+IN
-IN
dig.
Filter
Sensor
Interface IC
Fig. 1: Block diagram MS5540C
MS5540C Miniature Barome ter Module
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PIN CONFIGURATION
Fig. 2: Pin configuration of MS5540C
Pin Name
Pin
Type
Function
SCLK
1
I
Serial data cloc k
GND
2
G
Ground
PV (1)
3
N
Negative programming voltage
PEN (1)
4
I
Programming enable
VDD
5
P
Positive supply voltage
MCLK
6
I
Master clock (32.768 kHz)
DIN
7
I
Serial data input
DOUT
8
O
Serial data output
NOTE
1) Pin 3 (PV) and Pin 4 (PEN) are only used by the manufacturer for calibration purposes and should not be
connected.
ABSOLUTE MAXIM UM RATINGS
Parameter
Symbol
Conditions
Min
Max
Unit
Notes
Supply voltage
VDD
Ta = 25 °C
-0.3
4
V
Storage temperature
TS
-40
+85
°C
1
Overpressure
P
Ta = 25 °C
10
bar
2
NOTES
1) Storage and operation in an environment of dry and non-corrosive gases.
2) The MS5 540C is qual ified r efer ring to th e ISO 228 1 st andard and ca n withstand an absol ute pr essur e of 11
bar in salt water or 100 m water respectively.
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RECOMMENDED O PERATING CONDITIONS
(Ta = 25 °C, VDD = 3.0 V unless noted otherwise)
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Operating pressure range p 10 1100
mbar
abs.
Supply voltage
VDD
2.2
3.0
3.6
V
Supply current,
average (1)
during conversion (2)
standby (no conversion)
Iavg
Isc
Iss
V
DD
= 3.0 V
4
1
0.1
µA
mA
µA
Current consumption into MCLK
(3)
MCLK = 32.768 kHz 0.5 µA
Operating temperature range
T
-40
+85
°C
Conversion time
tconv
MCLK = 32.768 kHz
35
ms
External clo ck signal (4)
MCLK
30.000
32.768
35.000
kHz
Duty cycle of MCLK
40/60
50/50
60/40
%
Serial data cloc k
SCLK
500
kHz
NOTES
1) Under the assumption of one conversion every second. Conversion means either a pressure or a
temperature measurement started by a command to the serial interface of MS5540C.
2) During conversion the sensor will be switched on and off in order to reduce power consumption; the total on
time within a conversion is about 2 ms.
3) This value can be reduced by switching off MCLK while MS5540C is in standby mode.
4) It is strongly recommended that a crystal oscillator be used because the device is sensitive to clock jitter. A
square-wave form of the clock signal is a must.
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ELECTRICAL CHARACTERISTICS
DIGITAL INPUTS
(T = -40 °C .. 85 °C, VDD = 2.2 V .. 3.6 V)
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Input High Voltage
VIH
80% VDD
100% VDD
V
Input Low Voltag e
VIL
0% VDD
20% VDD
V
Signal Rise Time
tr
200
ns
Signal Fall Time
tf
200
ns
DIGITAL OUTPUTS
(T = -40 °C .. 85 °C VDD = 2.2 V .. 3.6 V)
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Output High Voltage
V
OH
I
source
= 0.6 mA
80% V
DD
100% V
DD
V
Output Low Voltage
VOL
Isink = 0.6 mA
0% VDD
20% VDD
V
Signal Rise Time
tr
200
ns
Signal Fall Time
tf
200
ns
AD-CONVERTER
(T = -40 °C .. 85 °C VDD = 2.2 V .. 3.6 V)
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Resolution
16
Bit
Linear Range
4'000
40'000
LSB
Conversion Time
MCLK = 32.768 kHz
35
ms
INL
Within linear rang e
-5
+5
LSB
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PRESSURE OUTPUT CHARACTERISTICS
With the calibration data stored in the interface IC of the MS5540C, the following characteristics can be
achieved: (VDD = 3.0 V unless noted otherwise)
Parameter
Conditions
Min
Typ
Max
Unit
Notes
Resolution
0.1
mbar
1
Absolute Pressure Accuracy
p =750 .. 1100 mbar
Ta = 25°C
-1.5 +1.5 mbar 2
Relative Pressure Accuracy
p =750 .. 1100 mbar
Ta = 25°C
-0.5 +0.5 mbar 3
Relative Pressure Error over
Temperature
T = 0 .. +50°C
p =300 .. 1000 mbar
-1 +1 mbar 4
T = -40 .. +85°C
p =300 .. 1000 mbar
-2 +5 mbar 4
Long-term Stability
12 months
-1
mbar
5
Maximum Error over Supply
Voltage
V
DD
= 2.2 .. 3.6 V
p = const.
-1.6 1.6 mbar
NOTES
1) A stable pressure reading of the given resolution requires taking the average of 2 to 4 subsequent pressure
values due to noise of the ADC.
2) Maximum error of pressure reading over the pressure range.
3) Maximum error of pressure reading over the pressure range after offset adjustment at one pressure point.
4) With the second-order temperature compensation as described in Section "FUNCTION". See next section
for typical operating curves.
5) The long-term stability is measured with non-soldered dev ic es.
TEMPERATURE OUTPUT CHARACTERISTICS
This temperature information is not required for most applications, but it is necessary to allow for temperature
compensation of the output. (VDD = 3.0 V unless noted otherwise)
Parameter
Conditions
Min
Typ
Max
Unit
Notes
Resolution
0.005
0.01
0.015
°C
Accuracy
T = 20 °C
-0.8
0.8
°C
T = -40 .. + 85°C
-2
+2
°C
1
Maximum Error over Supply
Voltage
VDD = 2.2 .. 3.6 V -0.2 +0.2 °C 2
NOTES
1) With the second-order temperature compensation as described in Section "FUNCTION". See next section
for typical operating curves.
2) At Ta = 25 °C.
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TYPICAL PERFORMANCE CURVES
ADC-value D1 vs Pressure (typical)
6000
8000
10000
12000
14000
16000
18000
20000
22000
0100 200 300 400 500 600 700 800 900 1000 1100
Pressure (mbar)
ADC-value D1 (LSB)
-40°C
25°C
85°C
ADC -value D2 vs Temperature (typical)
15000
20000
25000
30000
35000
40000
-40 -20 020 40 60 80
Temperature (°C)
ADC-value D2 (LSB)
Abso lute Pressure Accuracy after Calibr ation, 2nd order compensation
-4
-3
-2
-1
0
1
2
3
4
0100 200 300 400 500 600 700 800 900 1000 1100
Pressure (mbar)
Pressure error (mbar)
85°C
60°C
25°C
0°C
-40°C
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Temperature Error Accuracy vs temperature (typical)
-5
0
5
10
15
-40 -20 020 40 60 80
Temperat ure (°C)
Temperature error (°C)
Temperature error (st andard
calculation)
Temperature error (with 2nd
order calculati on)
Pressure Error Accuracy vs temperature (typical)
-8
-6
-4
-2
0
2
4
6
8
10
12
14
16
18
-40 -20 020 40 60 80
Temperature (°C)
Pressure error (mbar)
Perror(1000,1st order)
Perror(1000,2nd order)
Perror(800,1st order)
Perror(800,2nd order)
Perror(300,1st order)
Perror(300,2nd order)
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Pressure error vs supply voltage (typical)
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
2.2 2.4 2.6 2.8 33.2 3.4 3.6
Voltage (V)
Pressure error (mb ar)
1000mbar
800mbar
300mbar
Temperature error vs supply voltage (typical)
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
2.2 2.4 2.6 2.8 33.2 3.4 3.6
Voltage (V)
Temperature error (°C)
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FUNCTION
GENERAL
The MS5540C consists of a piezo-resistive sensor and a sensor interface IC. The main function of the MS5540C
is to convert the uncompensated analogue output voltage from the piezo-resistive pressure sensor to a 16-bit
digital value, as well as pro vidin g a 16-bit digital value for the temperature of the sensor.
Measured pressure (16-bit) “D1”
Measured temperature (16-bit) “D2”
As the output voltage of a pressure sensor is strongly dependent on temperature and process tolerances, it is
necessar y to compens ate for thes e effect s. This com pensation proce dure mus t be perform ed by software us ing
an external microcontroller.
For both pressure and temperature measurement the same ADC is used (sigma delta converter):
• for the pressure measurement, the differential output voltage from the pressure sensor is converted
• for the temperature measurement, the sensor bridge resistor is sensed and converted
During both measurements the sensor will only be switched on for a very short time in order to reduce power
consumption. As both, the bridge bias and the reference voltage for the ADC are derived from VDD, the digital
output data is independent of the supply voltage.
FACTORY CALIBRATION
Every m odule is indi viduall y factor y calibrated at t wo t em peratures and two press ures. As a result, 6 c oeff icients
necessar y to com pens ate for proces s var iations and t em perature var iat ions ar e calc ulate d and stor ed in the 64-
bit PROM of each module. These 64-bit (partitioned into four words of 16-bit) must be read by the
microcontroller software and used in the program converting D1 and D2 into compensated pressure and
temperature values.
PRESSURE AND TEMPERATURE MEASUREMENT
The sequence of reading pressure and temperature as well as of performing the software compensation is
depicted in Fig. 3 and Fig. 5.
First Word1 to Word4 have to be read through the serial interface. This can be done once after reset of the
microcontroller that interfaces to the MS5540C. Next, the compensation coefficients C1 to C6 are extracted
using bit-wise logical- and shift-operations (refer to Fig. 4 for the bit-pattern of Word1 to Word4).
For the pressure measurement, the microcontroller has to read the 16-bit values for pressure (D1) and
temper ature (D2) via the ser ial interface in a loo p (for instance ev ery second). T hen, the com pensated pres sure
is calculated out of D1, D2 and C1 to C6 according to the algorithm in Fig. 3 (possibly using quadratic
temperature compensation according to Fig. 5). All calculations can be performed with signed 16-bit variables.
Results of m ultiplicat ions m ay be u p to 32-b it lon g (+si gn). In the f low accor ding to F ig. 3 a divis ion f ollows e ach
Sensor
D1
D2
Word 1..4
Calculation
in external
micro-
controller
Pressure
Temperature
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multiplication. This division can be performed by bit-wise shifting (divisors are to the power of 2). It is ensured
that the results of these divisions are less than 65536 (16 bit).
For the timing of signals to read out Word1 to Word4, D1, and D2 please refer to the paragraph “Serial
Interface".
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System
initialisation
Pressure and temperature measurement
Example:
Word1, Word2, Word3 and Word4 (4x16 Bit)
D1 = 16460
D2 = 27856
Start
Convert calibration data into coefficients:
(see bit pattern of Word1-Word4)
Read calibration data (factory calibrated) from
PROM of MS5540C
Read digital pressure value from MS5540C
D1 (16 Bit)
Read digital temperature value from MS5540C
Display pressure and temperature value
Basic equations:
Calculate calibration temper at ure
UT1 = 8*C5+20224
Calculate tem perat ur e co mpensated pressure
Difference between actual temperature and reference
temperature:
dT = D2 - UT1
Actual tem pe ra tur e:
TEMP = 200 + dT*(C6+50)/2
10
(0.1°C resolution)
Calculate act ual tem perat ur e
D2 (16 Bit)
SENST1
OFFT1
TCS
TCO
T
ref
TEMPSENS
C1: Pressure sensitivity (15 Bit)
C2: Pressure offset (12 Bit)
C3: Temperature coefficient of pressure sensitivity (10 Bit)
C4: Temperature coefficient of pressure offset (10 Bit)
C5: Reference Temperature (11 Bit)
C6: Temperature coefficient of the temperature (6 Bit)
(
Refer to application note AN516 for limits of coefficients and
calculated results)
Word1 = 46940
Word2 = 40217
Word3 = 25172
Word4 = 47212
C1 = 23470
C2 = 1324
C3 = 737
C4 = 393
C5 = 628
C6 = 25
dT(D2) = D2 - T
ref
TEMP(D2) = 20°+dT(D2)*TEMPSENS
Offset at actual temperature:
OFF = C2*4 + ((C4-512)*dT)/2
12
Sensitivity at actual temperature:
SENS = C1 + (C3*dT)/2
10
+ 24576
X = (SENS * (D1-7168))/2
14
- OFF
Temperature compensated pressure:
P = X*10/2
5
+ 250*10 (0.1 mbar resolution)
OFF(D2) = OFFT1+TCO*dT(D2)
SENS(D2) = SENST1+TCS*dT(D2)
P(D1,D2) = D1*SENS(D2)-OFF(D2)
dT = 2608
TEMP = 391
= 39.1 °C
OFF = 5220
SENS = 49923
X = 23093
P = 9716
= 971.6 mbar
UT1 = 25248
Fig. 3: Flow chart for pressure and temperature reading and software compensation
NOTES
1) Readings of D2 can be done less frequently, but the display will be less stable in this case.
2) For a stable display of 1 mbar resolution, it is recommended to display the average of 8 subsequent
pressure values.
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C1 (15 Bit)
C5/I
1 Bit
Word1 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB10
C5/II (10 Bit)
C6 (6 Bit)
Word2 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB5 DB4 DB3 DB2 DB1 DB0
C4 (10 Bit)
C2/I (6 Bit)
Word3 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB11 DB10 DB9 DB8 DB7 DB6
C3 (10 Bit)
C2/II (6-Bit)
Word4 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB5 DB4 DB3 DB2 DB1 DB0
Fig. 4: Arrangement (Bit-pattern) of calibrat ion data in Word1 to Word4
SECOND-ORDER TEMPERATURE COMPENSATION
In order to obtain full temperature accuracy over the whole temperature range, it is recommended to
compens ate f or the n on-l inear ity of the outp ut of the t e mperature s ens or. This can be achiev ed by correcting the
calculated temperature and pressure by a second order correction factor. The second-order factors are
calculated as follows:
No correction
T2 = 0
P2 = 0
High Temperatures
T2 = 3*(C6+24)*(450 - TEMP)*(450 – TEMP) / 2
20
P2 = T2 * (P - 10000)/2
13
TEMP < 200
yes
Calculate pressure and temperature
TEMP = TEMP – T2
P = P – P2
Low Temperatures
T2 = 11*(C6+24)*(200 - TEMP)*(200 – TEMP) / 2
20
P2 = 3 *T2 * (P - 3500)/2
14
TEMP > 450
yes
200 ≤ TEMP ≤ 450
yes
Fig. 5: Flow chart for calculating the temperature and pressure to the optimum accuracy.
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SERIAL INTERFACE
The MS5540C communicates with microprocessors and other digital systems via a 3-wire synchronous serial
interface as shown in Fig. 1. The SCLK (Serial clock) signal initiates the communication and synchronizes the
data trans fer with each bit bei ng sampled b y the MS5540C on the r ising edge of SCL K and each bit bein g sent
by the MS5540C on the rising edge of SCLK. The data should thus be sampled by the microcontroller on the
falling edg e of SCLK and s ent to the MS5540C with th e fallin g edge of SCL K. T he SCLK-s ignal is gen erate d b y
the microprocessor’s system. The digital data provided by the MS5540C on the DOUT pin is either the
conversion result or the software calibration data. In addition, the signal DOUT (Data out) is also used to
indicate t he conversi on status (conversion-r eady signa l, see belo w). The selec tion of the output data is done by
sending the corresponding instruction on the pin DIN (Data input).
Following is a list of possible output data instructions:
• Conversion start for pressure measurement and ADC-data-out “D1” (Figure 6a)
• Conversion start for temperature measurement and ADC-data-out “D2” (Figure 6b)
• Calibration data read-out sequence for Word1 (Figure 6c)
• Calibration data read-out sequence for Word2 (Figure 6d)
• Calibration data read-out sequence for Word3 (Figure 6c)
• Calibration data read-out sequence for Word4 (Figure 6d)
• RESET sequence (Figure 6e)
Every communication starts with an instruction sequence at pin DIN. Fig. 6 shows the timing diagrams for the
MS5540C. The device does not need a ‘Chip select’ signal. Instead there is a START sequence (3-Bit high)
before each SETUP sequence and STOP sequence (3-Bit low) after each SETUP sequence. The SETUP
sequence consists in 4-Bit that select a reading of pressure, temperature or calibration data. In case of
pressure- (D1) or temperatur e- (D2) read in g th e module ack no wledges t he s t ar t o f a c onvers i on by a low to h igh
transition at pin DOUT.
Two additional clocks at SCLK are required after the acknowledge signal. Then SCLK is to be held low by the
microcontroller until a high to low transition on DOUT indicates the end of the conversion.
This signal can be used to create an interrupt in the m icrocontroller. The microcontroller may now read out the
16 bit word b y giving a not h er 17 c locks on the SLCK pin. It is poss ib le to i nterr up t the dat a R EAD OUT sequence
with a hol d of the SCLK s ignal. It is important to always read out the last conversion result before starting
a new conversion.
The RESET sequence is special as the module in any state recognizes its unique pattern. By consequence, it
can be used to restart if synchronization between the microcontroller and the MS5540C has been lost. This
sequence is 21-bit long. T he DOUT signal m ight change duri ng that seq uence (s ee Fig. 6e). It is rec ommended
to send the RESET sequence before each CONVERSION sequence to avoid hanging up the protocol
permanently in case of electrical interference.
sequence: START+P-measurement
SCLKDOUTDIN
Bit7
Conversion start for pressure measurement and ADC-data-out "D1":
end of co nve rsion
Bit6Bit5Bit4Bit3Bit2Bit1Bit0
conversion
(33ms)
DB7
ADC-data ou t MSB ADC-data o ut LSB
Bit8 Bit9
Start-bit Stop-bit
DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
start of conversion
Setup-bits
Fig. 6a: D1 ACQUISITION sequence
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sequence: START+T-measurement
SCLK
DOUT
DIN
Bit7
Conversion start for temperature measurement and ADC-data-out "D2":
end of co nve rsion
Bit6Bit5Bit4Bit3Bit2Bit1Bit0
conversion
(33ms)
Bit8 Bit9
Start-bit Stop-bitSetup-bits
start of conversion
DB7
ADC-data ou t MSB ADC-data o ut LSB
DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
Fig. 6b: D2 ACQUISITION sequence
sequence: coefficient r ead + address
SCLKDOUTDIN
Bit7
Calibration data read out sequence for word 1/ word 3:
Bit6Bit5Bit4Bit3Bit2Bit1Bit0
DB7
coefficient-data ou t MSB coefficient-data o ut LSB
Bit8 Bit9
Start-bit Stop-bit
DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
Bit10 Bit11
address word 1
address word 3
Setup-bits
Fig. 6c: Word1, Word3 READING sequence
address word 2
address word 4
sequence: coefficient r ead + address
SCLK
DOUT
DIN
Bit7
Calibration data read out sequence for word 2/ word 4:
Bit6Bit5Bit4Bit3Bit2Bit1Bit0
DB7
coefficient-data ou t MSB coefficient-data o ut LSB
Bit8 Bit9
Start-bit Stop-bit
DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
Bit10 Bit11
Setup-bits
Fig. 6d: W2, W4 READING sequence
sequence: RESET
SCLK
DOUT
DIN
Bit7
RESET - sequence:
Bit6Bit5Bit4Bit3Bit2Bit1Bit0 Bit8 Bit9 Bit10 Bit11Bit12 Bit13 Bit14 Bit15 Bit16 Bit17 Bit18 Bit19 Bit20
Fig. 6e: RESET sequence (21 bit)
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APPLICATION INFORMATION
GENERAL
The advant age f or this c om binat ion of a sensor with a dir ectly adapted int egrat ed c irc uit is to s ave o ther external
components and to achieve very low power consumption. The main application field for this system includes
portable devices with battery supply, but its high accuracy and resolution make it also suited for industrial and
automot ive ap pl icati ons . The possib ility to compens ate the s ens or w ith sof t ware a l lo ws th e us er to a dapt it to his
particular application. Communication between the MS5540C and the widely available microcontrollers is
realised over an easy-to-use 3-wire serial interface. Customers may select which microcontroller system to be
used, and ther e are no spe cif ic standard inter face c ells r equired, wh ich m ay be of interes t for spec ially designed
4 Bit-microcontroller applications.
CALIBRATION
The MS5540C is factory calibrated. The calibration data is stored inside the 64 bit PROM memory.
SOLDERING
Please refer to the application note AN808 for all soldering issues.
HUMIDITY, WATER PROTECTION
The version MS5540-CM carries a metal protection cap filled with silicone gel for enhanced protection against
humidit y. T he pr o pert ies of this g el ens ur e f unc ti on of the s ens or even when in d ir ect wat er c ont ac t. This feat ur e
can be useful for waterproof watches or other applications, where direct water contact cannot be avoided.
Nevertheless the user should avoid drying of hard materials like for example salt particles on the silicone gel
surface. In this case it is better to rinse with clean water afterwards. Special care has to be taken to not
mechanically damage the gel. Damaged gel could lead to air entrapment and consequently to unstable sensor
signal, especially if the damage is close to the sensor surface.
The metal protection cap is fabricated of special anticorrosive stainless steel in order to avoid any corrosive
battery effects inside the final product. The MS5540CM was qualified referring to the ISO Standard 2281 and
can withst and a press ure of 11 bar in salt wat er. The conc entrat ion of the sea water used f or the qua lification is
41 g of see salt for 1 litre of DI water.
For under water operat ions as s pecified in I SO Stand ard 2281 i t is impor tant to se al the sensor with a rub ber O -
ring around the metal cap. Any salt water coming to the contact side (ceramic and pads) of the sensor could
lead to permanent damage. Especially for "water-resistant 100 m" watches it is recommended to provide a
stable mechanical pusher from the backside of the sensor. Otherwise the overpressure might push the sensor
backwards and even bend the electronic board on which the sensor is mounted.
LIGHT SENSITIVITY
The MS5540C is protected against sunlight by a layer of white gel. It is, however, important to note that the
sensor may still be slightly sensitive to sunlight, especially to infrared light sources. This is due to the strong
photo effect of silicon. As the effect is reversible there will be no damage, but the user has to take care that in
the final product the sensor cannot be exposed to direct light during operation. This can be achieved for
instance by placing mechanical parts with holes in such that light cannot pass.
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CONNECTION TO PCB
The package outline of the module allows the use of a flexible PCB to connect it. This can be important for
applications in watches and other special devices, and will also reduce mechanical stress on the device.
For applicat ions subjected to m echanical shock, it is recommended to enhance the m echanical reliability of the
solder junctions by covering the rim or the corners of MS5540C's ceramic substrate with glue or Globtop-like
material.
DECOUPLING CAPACITOR
Particular c ar e must be tak en wh en co nnec t ing the de vic e to p o wer sup ply. A 47 µF tanta lum capacitor must be
placed as close as possible of the MS5540C's VDD pin. This capacitor will stabilize the power supply during
data convers ion and thus, prov ide the hi ghest pos s ib le acc uracy.
APPLI CATION EXAM PLE: ALTIMETER SYSTEM USING MS5540C
MS5540C is a circ uit that c an be used in con nection with a microcontr oller in div ing computer a pplications. It is
designed for lo w-voltage s ystem s with a sup pl y voltage of 3V, p articu larl y in batt er y applicat ions. T he MS5540C
is optim ised for low current consumption as the AD-converter clock (MCLK) can use the 32.768 kH z frequency
of a standard watch crystal, which is supplied in most portable watch systems.
For applications in altimeter systems MEAS Switzerland can deliver a simple formula to calculate the altitude,
based on a linear interpolation, where the number of interpolation points influences the accuracy of the formula.
4/8bit-Microcontroller
LCD-Display
EEPROM
Keypad
MS5540C
SCLK
DIN
DOUT
MCLK
XTAL1
XTAL2
32.768 kHz
optional
VDD
GND
VDD
GND
3V-Battery
47µF
Tantal
Figure 7: Demonstration of MS5540C in a mobile altimeter
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RECOMMENDED PAD LAYOUT
Pad layout for bottom side of MS5540C soldered onto printed circuit board.
Fig. 10: Layout for bottom side
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DEVICE PACKAGE OUTLINES
Fig. 8: Device package outlines of MS5540-C
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ASSEMBLY
M ECHANICAL STR ES S
It is recom mended to avoid m echanic al str es s on the PCB on wh ich th e s ens or is mounted. T he th ic kness of the
PCB should not be below 1.6 mm. A thicker PCB is stiffer creating less stress on the soldering contacts. For
applications where mechanical stress cannot be avoided (for example ultrasound welding of the case or thin
PCB’s in watches) please fix the sensor with drops of low stress epoxy (for example Hysol FP-4401).
MOUNTING
The MS5540C can be placed with automatic Pick&Place equipment using vacuum nozzles. It will not be
damaged by the vacuum. Due to the low stress assembly the sensor does not show pressure hysteresis effects.
Special care has to be taken to not touch the protective gel of the sensor during the assembly.
The MS5540C can be mounted with the cap down or the cap looking upwards. In both cases it is important to
solder all contact pads. The Pins PEN and PV shall be left open or connected to VDD. Do not connect the
Pins PEN and PV to GND!
SEALING WITH O-RING
In products like outdoor watches the electronics must be protected against direct water or humidity. For those
products the M S5540-CM p rovi des the possibility to seal with an O -ring . The protec tive cap of t he M S5540CM is
made of special anticorrosive stainless steel with a polished surface. In addition to this the MS5540CM is filled
with silico ne gel cover ing the sens or and the b onding wires . The O -ring (or O-rings ) shall be plac ed at the outer
diameter of the metal cap. This method avoids mechanical stress because the sensor can move in vertical
direction.
CLEANING
The MS5540C has been manufactured under cleanroom conditions. Each device has been inspected for the
homogeneity and the cleanness of the silicone gel. It is therefore recommended to assemble the sensor under
class 10’000 or better conditions. Should this not be possible, it is recommended to protect the sensor opening
during ass embl y from entering p articles and d ust. T o avoid cleani ng of the PCB , solder pas te of type “ no-clean”
shall be used. Cleaning might damage the sensor!
ESD PRECAUTIONS
The electrical contact pads are protected against ESD up to 4 kV HBM (human body model). It is therefore
essentia l to ground machines and p er sonal pr o perly during as sembly and han dlin g of t he d evic e. The MS5540C
is shipped in antistatic transport boxes. Any test adapters or production transport boxes used during the
assembly of the sensor shall be of an equivalent antistatic material.
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ORDERING INFORMATION
Part Number / Art.
Number
Product
MEAS Production
Site
Delivery Form
325540009-00
MS5540-CM Miniature Barometer Module
Switzerland
Tube
325540009-50
MS5540-CM Miniature Barometer Module
Switzerland
Tape&Reel TOP-UP
325540009-08
MS5540-CM Miniature Barometer Module
China
FACTORY CONTACTS
NORTH AMERICA
EUROPE
ASIA
Measurement Specialties
45738 Northport Loop West
Fremont, CA 94538
Tel: +1 800 767 1888
Fax: +1 510 498 1578
e-mail: pfg.cs.amerameas-spec.com
Website: www.meas-spec.com
MEAS Switzerland Sàrl
Ch. Chapons-des-Prés 11
CH-2022 Bevaix
Tel: +41 32 847 9550
Fax: + 41 32 847 9569
e-mail: sales.chameas-spec.com
Website: www.meas-spec.com
Measurement Special ties (China), Ltd .
No. 26 Langshan Road
Shenzhen High-Tech Park (North)
Nanshan District, Shenzhen, 518057
China
Tel: +86 755 3330 5088
Fax: +86 755 3330 5099
e-mail: pfg.cs.asiaameas-spec.com
Website: www.meas-spec.com
The information in this sheet has been carefull y reviewed and is believed to be accurate; however, no responsibilit y is assumed for
inaccuracies. Furtherm ore, this inform ation does not convey to the purchaser of such devices any license under the patent rights to the
manufacturer. Measurem ent Specialt i es, Inc. reserves the right t o make changes without furt her notice to any product herein. Measurement
Specialti es, Inc. makes no warranty, represent ation or guarant ee regarding the sui t abili t y of its product for any particul ar purpos e, nor does
Measurement Specialti es, Inc. assume any liability arising out of the applic at i on or use of any product or circuit and specifically discl aims
any and all liabilit y, includi ng without limitation consequential or incidental damages. Typical parameters can and do vary in different
applicat i ons. All operat i ng parameters must be validated for each custom er appl ication by custom er’s tec hni cal experts. Measurement
Specialti es, Inc. does not convey any license under its patent rights nor the rights of others.