MS5541C (RoHS*) • • • • • • • • • MINIATURE 14 bar MODULE 0 - 14 bar absolute pressure range 6 coefficients for a software compensation stored on-chip Piezoresistive silicon micromachined sensor Integrated pressure sensor 6.2x6.4 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 MS5541C is the miniature version of MS5535C pressure sensor module. It contains a precision piezoresistive pressure sensor and an improved version of the 16 Bit Micropower Sensor interface IC known from the MS5535C. Compared to the previous version the ESD sensitivity has been improved to 4kV on all pins. In addition to this the MS5541C is from its outer dimensions compatible to the MS54xx series of pressure sensors. It uses an antimagnetic polished stainless steel ring for sealing with O-ring. The sensor provides 16 Bit pressure and temperature data via a 3 wire serial interface that can be easily interfaced with 4 Bit low power microcontrollers. 64 Bit of factory programmed PROM provides calibration data for a highly accurate pressure and temperature calculation. The MS5541C is fully software compatible to the MS5535C and previous versions of MS5541. FEATURES APPLICATIONS Resolution 1.2 mbar Supply voltage 2.2 V to 3.6 V Operating current < 5uA Standby current < 0.1uA -40°C to +85°C No external components required • • • • • • • • Diving computers and divers watches Mobile water depth measurement systems BLOCK DIAGRAM VDD MCLK Input MUX SENSOR Digital Interface +IN -IN ADC Sensor Interface IC DIN DOUT dig. Filter SCLK Memory (PROM) 64 bits SGND GND Fig.: 1 Block Diagram MS5541C * 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). DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 1 PIN CONFIGURATION Fig. 2: Pin configuration of MS5541C Pin Name Pin Type Function SCLK VSS 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 (do not connect) Programming enable (do not connect) Positive supply voltage Master clock (32.768kHz) Serial data input Serial data output NOTE 1) Pins 3 (PV) and 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 o Ta = 25 C Min Max Unit Notes -0.3 -40 4 +85 30 V C bar 1 2 o NOTES 1) Storage and operation in an environment of dry and non-corrosive gases. 2) The MS5541CM is qualified referring to the ISO 6425 standard and can withstand an absolute pressure of 30 bar in salt water. DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 2 RECOMMENDED OPERATING CONDITIONS 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 (16 Bit) External clock signal (4) Symbol p Conditions VDD 2.2 3.0 3.6 V 0.1 0.5 µA mA µA µA VDD = 3.0 V Iavg ISC Iss 4 1 MCLK=32768Hz Ta Tconv SCLK °C -40 +25 +85 35 ms 30000 32768 35000 Hz 40/60 50/50 60/40 % 500 kHz MCLK=32768Hz MCLK Duty cycle of MCLK Serial data clock (T=25°C, VDD=3.0V unless noted otherwise) Min. Typ. Max Unit 0 14 bar 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 MS5541C. 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 2ms. 3) This value can be reduced by switching off MCLK while MS5541C 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. DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 3 ELECTRICAL CHARACTERISTICS DIGITAL INPUTS Parameter Symbol Conditions Min (T = -40°C .. 85°C, VDD = 2.2 V .. 3.6 V) 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 Parameter (T=-40°C .. 85°C, VDD = 2.2V..3.6V) Typ Max Unit Symbol Conditions Min Output High Voltage VOH ISource = 0.6 mA 80% VDD 100% VDD 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 Parameter Symbol Conditions Min Resolution INL DA5541C_004.doc 0005541C1194 ECN1118 (T=25°C, VDD =3.0V) Max Unit 16 Linear Range Conversion Time Typ 4000 MCLK=32768Hz within linear Range June 16th, 2008 -5 Bit 40000 LSB 35 ms 5 LSB 4 PRESSURE OUTPUT CHARACTERISTICS With the calibration data stored in the interface IC of the MS5541C the following characteristics can be achieved: (VDD = 3.0 V unless noted otherwise) Parameter Conditions Min Max Unit Note p = 0 .. 5bar p = 0 .. 10bar p = 0 .. 14bar p = 0 .. 5bar p = 0 .. 10bar p = 0 .. 14bar +20 +20 +20 +100 +180 +200 mbar mbar mbar mbar mbar mbar mbar 1 -20 -40 -100 -40 -60 -160 Ta = -40…+85°C -10 +100 mbar Resolution Absolute Pressure Accuracy (Temperature range 0 .. +40 °C) Absolute Pressure Accuracy (Temperature range -40 .. +85 °C) Error over Temperature (p = const. relative to 20°C) Long-term Stability Maximum Error over Supply Voltage Typ 1.2 6 months VDD = 2.2…3.6V 20 -16 mbar 16 2 3 4 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) With the second-order temperature compensation as described in Section “FUNCTION". See next section for typical operating curves. 4) 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. The reference temperature is 20°C. Parameter Conditions Resolution Accuracy Maximum Error over Supply Voltage Min Typ Max Unit 0.005 0.015 °C Ta = 20°C -0.8 0.8 °C Ta = -40…+85°C -2 +6 °C VDD = 2.2…3.6V -0.2 0.2 °C Note 1 NOTE 1) With the second-order temperature compensation as described in Section “FUNCTION". See next section for typical operating curves. DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 5 TYPICAL PERFORMANCE CURVES ADC-value D1 vs Pressure (typical) 30000 ADC-value D1 (LSB) 25000 -40°C 25°C 85°C 20000 15000 10000 0 2000 4000 6000 8000 10000 12000 14000 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) DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 6 Absolute Pressure Accuracy after Calibration, 1st order compensation 250 200 Pressure error (mbar) 150 85°C 60°C 100 25°C 0°C 50 -40°C 0 0 2000 4000 6000 8000 10000 12000 14000 -50 -100 Pressure (mbar) Absolute Pressure Accuracy after Calibration, 2nd order compensation 80 60 40 Pressure error (mbar) 20 85°C 0 0 2000 4000 6000 8000 10000 12000 14000 60°C 25°C 0°C -20 -40°C -40 -60 -80 -100 Pressure (mbar) DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 7 Temperature Error Accuracy vs temperature (typical) 15 Temperature error (°C) 10 Temperature error (standard calculation) Temperature error (with 2nd order calculation) 5 0 -40 -20 0 20 40 60 80 -5 Temperature (°C) Pressure Error Accuracy vs temperature (typical) 100 75 Pressure error (mbar) 50 Pres. error 4bar (1st order) 25 Pres. error 4bar (2nd order) 0 -40 -20 0 20 40 60 80 -25 -50 Temperature (°C) DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 8 Pressure error vs supply voltage (typical) 10 8 6 Pressure error (mbar) 4 14000 mbar 2 6000 mbar 0 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 1000 mbar -2 -4 -6 -8 -10 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 3.4 3.6 -0.05 -0.1 -0.15 Voltage (V) DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 9 FUNCTION GENERAL The MS5541C consists of a piezoresistive sensor and a sensor interface IC. The main function of the MS5541C is to convert the uncompensated analog output voltage from the piezoresistive pressure sensor into 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 re 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 flow chart, 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 MS5541C. 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 word 1 to word 4). 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”. DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 10 Basic equations: System initialisation Start Example: Read calibration data (factory calibrated) from PROM of MS5541 Word1 = 18556 Word2 = 49183 Word3 = 22354 Word4 = 28083 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 (13 Bit) (13 Bit) (10 Bit) (9 Bit) (12 Bit) (7 Bit) SENST1 OFFT1 TCS TCO Tref TEMPSENS C1 = 2319 C2 = 4864 C3 = 349 C4 = 219 C5 = 2002 C6 = 51 Read digital pressure value from MS5541 D1 (16 Bit) D1 = 17788 Read digital temperature value from MS5541 D2 (16 Bit) D2 = 26603 Calculate calibration temperature UT1 = 26016 UT1=8*C5+10000 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 = 243 = 24.3 °C 11 TEMP = 200 + dT*(C6+100)/2 (0.1°C) = 587 Calculate temperature compensated pressure OFF(D2)=OFFT1+TCO*dT(D2) Offset at actual temperature: OFF = C2 + ((C4-250)*dT)/212 + 10000 SENS(D2)=SENST1+TCS*dT(D2) Sensitivity at actual temperature: OFF = 14859 SENS = C1/2 + ((C3+200)*dT)/213 + 3000 SENS = 4198 Temperature compensated pressure in mbar: P = (SENS * (D1-OFF))/212 + 1000 P(D1,D2)=D1*SENS(D2)-OFF(D2) P = 4001 = 4001 mbar Display pressure and temperature value Fig. 3: Flow chart for pressure/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 4 to 8 subsequent pressure values. DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 11 C1 (13 Bit) Word 1 DB12 DB11 DB10 DB9 DB8 DB7 DB6 C2/I (3 Bit) DB5 DB4 DB3 DB2 DB1 C2/II (10 Bit) Word 2 DB9 DB8 DB7 DB6 DB5 DB4 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB11 DB10 DB8 DB7 DB6 DB5 DB4 DB11 DB10 DB9 DB7 DB6 DB2 DB1 DB0 DB2 DB1 DB0 DB8 C5/II (6 Bit) DB3 DB2 DB1 DB0 DB5 DB4 C4 (9 Bit) Word 4 DB12 C5/I (6 Bit) C3 (10 Bit) Word 3 DB0 DB3 C6 (7-Bit) DB3 DB2 DB1 DB1 DB6 DB5 DB4 DB3 Fig. 4: Arrangement (Bit-pattern) of calibration 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 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: dT < 0 dT ≥ 0 yes yes Low Temperatures High Temperatures dT2 = dT – (dT/128*dT/128)/2 dT2 = dT – (dT/128*dT/128)/8 Calculate temperature 11 TEMP = (200 + dT2*(C6+100)/2 ) (0.1°C) Fig. 5: Flow chart for calculating the temperature and pressure to the optimum accuracy. DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 12 SERIAL INTERFACE The MS5541C 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 transfer with each Bit being sampled by the MS5541C on the rising edge of SCLK and each Bit being sent by the MS5541C 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 MS5541C with the falling edge of SCLK. The SCLK-signal is generated by the microprocessor’s system. The digital data provided by the MS5541C 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 word 1 Calibration data read-out sequence for word 2 Calibration data read-out sequence for word 3 Calibration data read-out sequence for word 4 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 MS5541C. 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 read-out 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 recognized by the module in any state. By consequence it can be used to restart if synchronization between the microcontroller and the MS5541C 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 DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 13 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: W1, W3 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 RESET - sequence: DIN DOUT SCLK Fig. 6d: W2, W4 reading sequence sequence: RESET Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7 Bit8 Bit9 Bit10 Bit11Bit12 Bit13 Bit14 Bit15 Fig. 6e: Reset sequence (21-Bit) DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 14 APPLICATION INFORMATION GENERAL The advantage for this combination of a 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 MS5541C 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 MS5541C 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 MS5541C 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 MS5541C was qualified referring to the ISO 6425 standard and can withstand a pressure of 30 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 like specified in ISO 6425 standard it is important to seal the sensor with a rubber ORing around the metal Ring. Any salt water coming to the contact side (ceramic and Pads) of the sensor could lead to permanent damage. For "water-resistant" 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 standard version of MS5541C 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 MS5541C's ceramic substrate with glue or Globtop like material. DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 15 DECOUPLING CAPACITOR Particular care must be taken when connecting the device to power supply: A 47µF tantalum capacitor must be placed as close as possible of the MS5541C's VDD pin. This capacitor will stabilize the power supply during data conversion and thus, provide the highest possible accuracy. APPLICATION EXAMPLE: DIVING COMPUTER SYSTEM USING MS5541C MS5541C is a circuit that can be used in connection with a microcontroller in diving computer applications. It is designed for low-voltage systems with a supply voltage of 3V, particularly in battery applications. The MS5541C 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 MS5541 VDD 47µF Tantal XTAL2 Keypad MCLK DIN DOUT SCLK GND 4/8bit-Microcontroller GND EEPROM optional Fig. 7: Demonstration of MS5541C in a diving computer RECOMMENDED PAD LAYOUT Pad layout for bottom side of MS5541C soldered onto printed circuit board Fig. 8: Pad layout of MS5541C DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 16 DEVICE PACKAGE OUTLINES Fig. 9: Device package outlines of MS5541C DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 17 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 be not 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 MS5541C 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 diving computers the electronics must be protected against direct water or humidity. For those products the MS5541C provides the possibility to seal with an O-ring. The protective cap of the MS5541C is made of special anticorrosive stainless steel with a polished surface. In addition to this the MS5541C 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 MS5541C 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 according 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 MS5541C 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. DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 18 ORDERING INFORMATION Product Code Product MS5541-CM Miniature 14 bar module white gel MS5541-CM Miniature 14 bar module cap transparent gel Art.-Nr. 325541009 325541008 Package SMD hybrid with solder paste, anticorrosive and antimagnetic metal protection cap, white silicon gel sensor protection SMD hybrid with solder paste, anticorrosive and antimagnetic metal protection cap, transparent silicon gel sensor protection Comments standard version same as standard version but different gel protection 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. DA5541C_004.doc 0005541C1194 ECN1118 June 16th, 2008 19