Intersema MS5540-CM Miniature barometer module Datasheet

MS5540C (RoHS*)
MINIATURE BAROMETER MODULE
• 10 - 1100 mbar absolute pressure range
• 6 coefficients 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
• RoHS-compatible & Pb-free*
DESCRIPTION
The MS5540C is a SMD-hybrid device including a precision piezoresistive pressure sensor and an ADCInterface 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 microcontroller.
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 sensitivity level has been improved to 4kV on all pins. The gel protection of the sensor provides a water
protection sufficient for 100 m waterproof watches without any additional protection.
FEATURES
•
•
•
•
•
•
APPLICATIONS
Resolution 0.1 mbar
Supply voltage 2.2 V to 3.6 V
Low supply current < 5 µA
Standby current < 0.1 µA
-40°C to +85°C operation temperature
No external components required
•
•
•
•
Mobile altimeter/barometer systems
Weather control systems
Adventure or multi-mode watches
GPS receivers
BLOCK DIAGRAM
VDD
MCLK
Input MUX
SENSOR
+IN
-IN
Digital
Interface
ADC
Sensor
Interface IC
DIN
DOUT
dig.
Filter
SCLK
Memory
(PROM)
64 bits
SGND
GND
Fig. 1: Block diagram MS5540C.
*
The European RoHS directive 2002/95/EC (Restriction of the use of certain Hazardous Substances in electrical and electronic equipment)
bans the use of lead, mercury, cadmium, hexavalent chromium and polybrominated biphenyls (PBB) or polybrominated diphenyl ethers
(PBDE).
DA5540C_003
0005540C1193 ECN 1118
June 16th, 2008
1
PIN CONFIGURATION
Fig. 2: Pin configuration of MS5540C.
Pin Name
Pin
Type
Function
SCLK
GND
PV (1)
PEN (1)
VDD
MCLK
DIN
DOUT
1
2
3
4
5
6
7
8
I
G
N
I
P
I
I
O
Serial data clock
Ground
Negative programming voltage
Programming enable
Positive supply voltage
Master clock (32.768 kHz)
Serial data input
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 MAXIMUM RATINGS
Parameter
Supply voltage
Storage temperature
Overpressure
Symbol
VDD
TS
P
Conditions
o
Ta = 25 C
Ta = 25 oC
Min
Max
Unit
Notes
-0.3
-40
4
+85
10
V
C
bar
1
2
o
NOTES
1) Storage and operation in an environment of dry and non-corrosive gases.
2) The MS5540C is qualified referring to the ISO Standard 2281 and can withstand an absolute pressure of 11
bar in salt water or 100 m water respectively.
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June 16th, 2008
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RECOMMENDED OPERATING CONDITIONS
(Ta = 25°C, VDD = 3.0 V unless noted otherwise)
Parameter
Operating pressure range
Supply voltage
Supply current,
average (1)
during conversion (2)
standby (no conversion)
Current consumption into
MCLK (3)
Operating temperature
range
Conversion time
External clock signal (4)
Symbol
Conditions
p
Typ.
10
VDD
2.2
Max
3.6
mbar
abs.
V
0.1
µA
mA
µA
0.5
µA
+85
°C
35
ms
1100
3.0
Unit
VDD = 3.0 V
Iavg
Isc
Iss
4
1
MCLK = 32.768 kHz
T
tconv
-40
+25
MCLK = 32.768 kHz
MCLK
Duty cycle of MCLK
Serial data clock
Min.
SCLK
30.000
32.768
35.000
kHz
40/60
50/50
60/40
%
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.
DA5540C_003
0005540C1193 ECN 1118
June 16th, 2008
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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 Voltage
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
Output High Voltage
VOH
Isource = 0.6 mA
Output Low Voltage
VOL
Isink = 0.6 mA
Typ
Max
Unit
80% VDD
100% VDD
V
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
Resolution
INL
DA5540C_003
0005540C1193 ECN 1118
Max
16
Linear Range
Conversion Time
Typ
4000
MCLK = 32.768
kHz
Within linear
range
-5
June 16th, 2008
Unit
Bit
40000
LSB
35
ms
+5
LSB
4
PRESSURE OUTPUT CHARACTERISTICS
With the calibration data stored in the interface IC of the MS5540C the following characteristics can be achieved:
Parameter
Conditions
Min
Resolution
Absolute Pressure Accuracy
Relative Pressure Accuracy
Relative Pressure Error over
Temperature
Long-term Stability
Maximum Error over Supply
Voltage
(VDD = 3.0 V unless noted otherwise)
Typ
Max
Unit
Notes
0.1
p = 750 .. 1100 mbar
Ta = 25°C
p = 750 .. 1100 mbar
Ta = 25°C
T = 0 .. +50°C
p = 300 .. 1000 mbar
T = -40 .. +85°C
p = 300 .. 1000 mbar
12 months
VDD = 2.2 .. 3.6 V
p = const.
mbar
1
-1.5
+1.5
mbar
2
-0.5
+0.5
mbar
3
-1
+1
mbar
4
-2
+5
mbar
4
mbar
5
-1
-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 devices.
TEMPERATURE OUTPUT CHARACTERISTICS
This temperature information is not required for most applications, but it is necessary to allow for temperature
compensation of the pressure output.
(VDD = 3.0 V unless noted otherwise)
Parameter
Conditions
Min
Typ
Max
Unit
Notes
Resolution
Accuracy
Maximum Error over Supply
Voltage
0.005
0.01
0.015
°C
T = 20°C
-0.8
0.8
°C
T = -40 .. +85°C
-2
+3
°C
1
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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0005540C1193 ECN 1118
June 16th, 2008
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TYPICAL PERFORMANCE CURVES
ADC-value D1 vs Pressure (typical)
22000
20000
ADC-value D1 (LSB)
18000
16000
-40°C
25°C
85°C
14000
12000
10000
8000
6000
0
100
200
300
400
500
600
700
800
900
1000
1100
Pressure (mbar)
ADC-value D2 vs Temperature (typical)
40000
ADC-value D2 (LSB)
35000
30000
25000
20000
15000
-40
-20
0
20
40
60
80
Temperature (°C)
Absolute Pressure Accuracy after Calibration, 2nd order compensation
4
3
Pressure error (mbar)
2
1
85°C
60°C
0
25°C
0°C
-40°C
-1
-2
-3
-4
0
100
200
300
400
500
600
700
800
900
1000
1100
Pressure (mbar)
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Temperature Error Accuracy vs temperature (typical)
15
Temperature error (°C)
10
Temperature error (standard
calculation)
Temperature error (with 2nd
order calculation)
5
0
-5
-40
-20
0
20
40
60
80
Temperature (°C)
Pressure Error Accuracy vs temperature (typical)
18
16
14
12
Pressure error (mbar)
10
8
Perror(1000,1st order)
Perror(1000,2nd order)
6
Perror(800,1st order)
4
Perror(800,2nd order)
Perror(300,1st order)
2
Perror(300,2nd order)
0
-2
-4
-6
-8
-40
-20
0
20
40
60
80
Temperature (°C)
DA5540C_003
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June 16th, 2008
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Pressure error vs supply voltage (typical)
1
0.8
0.6
Pressure error (mbar)
0.4
0.2
0
2.2
2.4
2.6
2.8
3
3.2
3.4
3.6
3.4
3.6
1000mbar
800mbar
300mbar
-0.2
-0.4
-0.6
-0.8
-1
Voltage (V)
Temperature error vs supply voltage (typical)
0.15
Temperature error (°C)
0.1
0.05
0
2.2
2.4
2.6
2.8
3
3.2
-0.05
-0.1
-0.15
Voltage (V)
DA5540C_003
0005540C1193 ECN 1118
June 16th, 2008
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FUNCTION
GENERAL
The MS5540C consists of a piezoresistive sensor and a sensor interface IC. The main function of the MS5540C
is to convert the uncompensated analogue output voltage from the piezoresistive pressure sensor to a 16-Bit
digital value, as well as providing a 16-Bit digital value for the temperature of the sensor.
• measured pressure (16-Bit)
• measured temperature (16-Bit)
“D1”
“D2”
As the output voltage of a pressure sensor is strongly dependent on temperature and process tolerances, it is
necessary to compensate for these effects. This compensation procedure must be performed by software using
an external microcontroller.
D1
Pressure
D2
Word1..4
Sensor
Calculation
in external
microcontroller
Temperature
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 module is individually factory calibrated at two temperatures and two pressures. As a result, 6 coefficients
necessary to compensate for process variations and temperature variations are calculated and stored in the 64Bit 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 the 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
temperature (D2) via the serial interface in a loop (for instance every second). Then, the compensated pressure
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 multiplications may be up to 32-Bit long (+sign). In the flow according to Fig. 3 each multiplication is
followed by a division. 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”.
DA5540C_003
0005540C1193 ECN 1118
June 16th, 2008
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Basic equations:
System
initialisation
Start
Example:
Read calibration data (factory calibrated) from
PROM of MS5540
Word1 = 46940
Word2 = 40217
Word3 = 25172
Word4 = 47212
Word1, Word2, Word3 and Word4 (4x16 Bit)
Convert calibration data into coefficients:
(see bit pattern of Word1-Word4)
Pressure and temperature measurement
C1: Pressure sensitivity
C2: Pressure offset
C3: Temperature coefficient of pressure sensitivity
C4: Temperature coefficient of pressure offset
C5: Reference Temperature
C6: Temperature coefficient of the temperature
(15 Bit)
(12 Bit)
(10 Bit)
(10 Bit)
(11 Bit)
(6 Bit)
SENST1
OFFT1
TCS
TCO
Tref
TEMPSENS
C1 = 23470
C2 = 1324
C3 = 737
C4 = 393
C5 = 628
C6 =
25
Read digital pressure value from MS5540
D1 (16 Bit)
D1 = 16460
Read digital temperature value from MS5540
D2 (16 Bit)
D2 = 27856
Calculate calibration temperature
UT1 = 25248
UT1 = 8*C5+20224
Calculate actual temperature
Difference between actual temperature and reference
temperature:
dT = D2 - UT1
Actual temperature:
dT(D2) = D2 - Tref
dT
TEMP(D2) = 20°+dT(D2)*TEMPSENS
TEMP = 391
= 39.1 °C
OFF(D2) = OFFT1+TCO*dT(D2)
OFF
SENS(D2) = SENST1+TCS*dT(D2)
SENS = 49923
10
TEMP = 200 + dT*(C6+50)/2 (0.1°C resolution)
= 2608
Calculate temperature compensated pressure
Offset at actual temperature:
OFF = C2*4 + ((C4-512)*dT)/212
Sensitivity at actual temperature:
= 5220
SENS = C1 + (C3*dT)/210 + 24576
X = (SENS * (D1-7168))/214 - OFF
Temperature compensated pressure:
P = X*10/25 + 250*10
(0.1 mbar resolution)
X
= 23093
P
= 9716
= 971.6 mbar
P(D1,D2) = D1*SENS(D2)-OFF(D2)
Display pressure and temperature value
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 0.1 mbar resolution, it is recommended to display the average of 8 subsequent
pressure values.
DA5540C_003
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June 16th, 2008
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C1 (15 Bit)
C5/I
1 Bit
Word1
DB14
DB13
DB12
DB11
DB10
DB9
DB8
DB7
DB6
DB5
DB4
DB3
C5/II (10 Bit)
Word2
DB9
DB8
DB7
DB6
DB5
DB4
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB5
DB4
DB9
DB8
DB7
DB6
DB5
DB4
DB0
DB10
DB3
DB2
DB1
DB0
DB7
DB6
DB1
DB0
C2/I (6 Bit)
DB3
DB2
DB1
DB0
DB11
DB10
C3 (10 Bit)
Word4
DB1
C6 (6 Bit)
C4 (10 Bit)
Word3
DB2
DB9
DB8
C2/II (6-Bit)
DB3
DB2
DB1
DB0
DB5
DB4
DB3
DB2
Fig. 4: Arrangement (Bit-pattern) of calibration data in Word1 to Word4.
SECOND-ORDER TEMPERATURE COMPENSATION
In order to obtain best accuracy over the whole temperature range, it is recommended to compensate for the
non-linearity of the output of the temperature sensor. This can be achieved by correcting the calculated
temperature and pressure by a second order correction factor. The second-order factors are calculated as
follows:
TEMP < 200
TEMP > 450
200 ≤ TEMP ≤ 450
yes
yes
yes
No correction
Low Temperatures
T2 = 11*(C6+24)*(200 - TEMP)*(200 – TEMP) / 220
14
P2 = 3 *T2 * (P - 3500)/2
High Temperatures
T2 = 0
T2 = 3*(C6+24)*(450 - TEMP)*(450 – TEMP) / 220
P2 = 0
P2 = T2 * (P - 10000)/213
Calculate pressure and temperature
TEMP = TEMP – T2
P = P – P2
Fig. 5: Flow chart for calculating the temperature and pressure to the optimum accuracy.
DA5540C_003
0005540C1193 ECN 1118
June 16th, 2008
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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 synchronises the
data transfer with each Bit being sampled by the MS5540C on the rising edge of SCLK and each Bit being sent
by the MS5540C on the rising edge of SCLK. The data should thus be sampled by the microcontroller on the
falling edge of SCLK and sent to the MS5540C with the falling edge of SCLK. The SCLK-signal is generated by
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
the conversion status (conversion-ready signal, see below). The selection 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
Conversion start for temperature measurement and ADC-data-out
Calibration data read-out sequence for Word1
Calibration data read-out sequence for Word2
Calibration data read-out sequence for Word3
Calibration data read-out sequence for Word4
RESET sequence
“D1”
“D2”
(Figure 6a)
(Figure 6b)
(Figure 6c)
(Figure 6d)
(Figure 6c)
(Figure 6d)
(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 temperature- (D2) reading the module acknowledges the start of a conversion by a low to high 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 microcontroller. The microcontroller may now read out the
16-Bit word by giving another 17 clocks on the SLCK pin. It is possible to interrupt the data READOUT sequence
with a hold of the SCLK signal. It is important to always read out the last conversion result before starting a
new conversion.
Conversion start for pressure measurement and ADC-data-out "D1":
end of conversion
start of conversion
conversion
(33ms)
ADC-data out MSB
DB7 DB6 DB5 DB4 DB3 DB2 DB1
DIN
DOUT SCLK
The RESET sequence is special as its unique pattern is recognised by the module in any state. By consequence
it can be used to restart if synchronisation between the microcontroller and the MS5540C has been lost. This
sequence is 21-Bit long. The DOUT signal might change during that sequence (see Fig. 6e). It is recommended
to send the RESET sequence before first CONVERSION sequence to avoid hanging up the protocol permanently
in case of electrical interference.
ADC-data out LSB
DB0 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
sequence: START+P-measurement
Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7 Bit8 Bit9
Start-bit
Setup-bits
Stop-bit
Fig. 6a: D1 ACQUISITION sequence.
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0005540C1193 ECN 1118
June 16th, 2008
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end of conversion
conversion
(33ms)
start of conversion
ADC-data out MSB
DB7 DB6 DB5 DB4 DB3 DB2 DB1
DIN
DOUT SCLK
Conversion start for temperature measurement and ADC-data-out "D2":
ADC-data out LSB
DB0 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
sequence: START+T-measurement
Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7 Bit8 Bit9
Start-bit
Setup-bits
Stop-bit
DIN
DOUT SCLK
Fig. 6b: D2 ACQUISITION sequence.
Calibration data read out sequence for word 1/ word 3:
coefficient-data out MSB
DB7 DB6 DB5 DB4 DB3 DB2 DB1
coefficient-data out LSB
DB0 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
sequence: coefficient read + address
Bit0 Bit1 Bit2
Bit3 Bit4 Bit5 Bit6 Bit7 Bit8 Bit9 Bit10 Bit11
Setup-bits
Start-bit
Stop-bit
address word 1
address word 3
DIN
DOUT SCLK
Fig. 6c: Word1, Word3 READING sequence.
Calibration data read out sequence for word 2/ word 4:
coefficient-data out MSB
DB7 DB6 DB5 DB4 DB3 DB2 DB1
coefficient-data out LSB
DB0 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
sequence: coefficient read + address
Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7 Bit8 Bit9 Bit10 Bit11
Setup-bits
Start-bit
Stop-bit
address word 2
address word 4
Fig. 6d: W2, W4 READING sequence.
DIN
DOUT SCLK
RESET - sequence:
sequence: RESET
Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7 Bit8 Bit9 Bit10 Bit11Bit12 Bit13 Bit14 Bit15
Fig. 6e: RESET sequence (21-Bit).
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APPLICATION INFORMATION
GENERAL
The advantage of combining a pressure sensor with a directly adapted integrated circuit is to save other 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
automotive applications. The possibility to compensate the sensor with software allows the user to adapt 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
there are no specific standard interface cells required, which may be of interest for specially designed 4 Bitmicrocontroller 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 silicon pressure transducer and the bonding wires are protected by an anticorrosive and antimagnetic
protection cap. The MS5540C carries a metal protection cap filled with silicone gel for enhanced protection
against humidity. The properties of this gel ensure function of the sensor even when in direct water contact. This
feature 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 and antimagnetic stainless steel in order to avoid
any corrosive battery effects inside the final product. The MS5540C is qualified referring to the ISO Standard
2281 and can withstand a pressure of 11 bar in salt water. The concentration of the see water used for the
qualification is 41 g of see salt for 1 litre of DI water.
For underwater operations as specified in ISO Standard 2281 it is important to seal the sensor with a rubber Oring 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.
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 applications subjected to mechanical shock, it is recommended to enhance the mechanical reliability of the
solder junctions by covering the rim or the corners of MS5540C's ceramic substrate with glue or Globtop-like
material.
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DECOUPLING CAPACITOR
Particular care must be taken when connecting the device to power supply. A 47 µF tantalum capacitor must be
placed as close as possible of the MS5540C's VDD pin. This capacitor will stabilise the power supply during data
conversion and thus, provide the highest possible accuracy.
APPLICATION EXAMPLE: ALTIMETER SYSTEM USING MS5540C
MS5540C is a circuit that can be used in connection with a microcontroller in mobile altimeter applications. It is
designed for low-voltage systems with a supply voltage of 3 V, particularly in battery applications. The MS5540C
is optimised for low current consumption as the AD-converter clock (MCLK) can use the 32.768 kHz frequency of
a standard watch crystal, which is supplied in most portable watch systems.
For applications in altimeter systems Intersema 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.
3V-Battery
LCD-Display
VDD
XTAL1
32.768 kHz
MS5540C
VDD
47µF
Tantal
XTAL2
Keypad
MCLK
DIN
DOUT
SCLK
GND
4/8bit-Microcontroller
GND
EEPROM
optional
Figure 7: Demonstration of MS5540C in a mobile altimeter.
RECOMMENDED PAD LAYOUT
Pad layout for bottom side of MS5540C soldered onto printed circuit board
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DEVICE PACKAGE OUTLINES
Fig. 8: Device package outlines of MS5540C.
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ASSEMBLY
MECHANICAL STRESS
It is recommended to avoid mechanical stress on the PCB on which the sensor is mounted. The thickness 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.
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 MS5540C provides the possibility to seal with an O-ring. The protective cap of the MS5540C is
made of special anticorrosive and antimagnetic stainless steel with a polished surface. In addition to this the
MS5540C is filled with silicone gel covering the sensor and the bonding wires. The O-ring (or O-rings) shall be
placed 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 assembly from entering particles and dust. To avoid cleaning of the PCB, solder paste 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
essential to ground machines and personal properly during assembly and handling of the device. 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
Product Code
MS5540-CM
Product
Art.-Nr.
Miniature
Barometer Module
with metal cap
325540009
Package
SMD hybrid with solder paste,
anticorrosive and antimagnetic
metal protection cap, silicon gel
sensor protection
Comments
Recommended
for outdoor
products
FACTORY CONTACTS
Intersema Sensoric SA
Ch. Chapons-des-Prés 11
CH-2022 BEVAIX
SWITZERLAND
Tel. 032 847 9550
Tel. Int. +41 32 847 9550
Telefax +41 32 847 9569
e-mail:
http://www.intersema.ch
NOTICE
Intersema reserves the right to make changes to the products contained in this data sheet in order to improve the design or performance
and to supply the best possible products. Intersema assumes no responsibility for the use of any circuits shown in this data sheet, conveys
no license under any patent or other rights unless otherwise specified in this data sheet, and makes no claim that the circuits are free from
patent infringement. Applications for any devices shown in this data sheet are for illustration only and Intersema makes no claim or
warranty that such applications will be suitable for the use specified without further testing or modification.
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