MS5534AM

MS5534A ♦ ♦ ♦ ♦ BAROMETER MODULE Integrated pressure sensor Pressure range 300-1100 mbar 15 Bit ADC 6 coefficients for a software compensation stored on-chip ♦ 3-wire serial interface ♦ 1 system clock line (32.768 kHz) ♦ Low voltage / low power DESCRIPTION The MS5534A is a SMD-hybrid device including a piezoresistive pressure sensor and an ADC-Interface IC. It provides a 16 Bit data word from a pressure- and temperature-dependent voltage. Additionally the module contains 6 readable coefficients for a highly accurate software calibration of the sensor. MS5534A is a lowpower, low-voltage device with automatic power down (ON/OFF) switching. A 3-wire interface is used for all communications with a microcontroller. Sensor packaging options are plastic or metal cap. FEATURES • • • • • • 15-Bit ADC resolution Supply voltage 2.2 V to 3.6 V Low Supply current -40°C to +60°C Small size No external components required APPLICATIONS • • • • Mobile altimeter/barometer systems W eather control systems Adventure or multi-mode watches GPS Receivers BLOCK DIAGRAM VDD MCLK Input MUX SENSOR +IN dig. Filter Digital Interface ADC DIN DOUT SCLK -IN Sensor Interface IC SGND Memory (PROM) 64 bits GND Fig.: 1 Block Diagram 5534 DA5534_022.doc ECN493 July 17th, 2002 1 PIN CONFIGURATION PEN 7 6 5 4 3 2 1 VDD MCLK DIN DOUT SCLK GND 6 5 4 3 2 1 PV 8 Fig. 2: Pin configuration of MS5534 PIN DESCRIPTION Pin Name VDD MCLK DIN DOUT SCLK GND PV PEN Pin 6 5 4 3 2 1 8 7 Type P I I O I G N I Function Positive Supply Voltage Master Clock (32.768kHz) Data Input Data Output Serial Data Clock Ground Negative Programming Voltage Programming Enable Note: Pins 7 (PEN) and 8 (PV) are only used by the manufacturer for calibration purposes and should not be connected. ABSOLUTE MAXIMUM RATINGS Parameter Supply Voltage Overpressure Storage Temperature Symbol VDD P TStg Conditions Min -0.3 Max 4 4 +70 Unit V bar abs o C -20 Notes: 1. Storage and operation in an environment of dry and non-corrosive gases. DA5534_022.doc ECN493 July 17th, 2002 2 RECOMMENDED OPERATING CONDITIONS (T=25°C, VDD=3.0V unless noted otherwise) Parameter Supply Voltage Supply Current, average (1) during conversion (2) standby (no conversion) Current consumption into MCLK (3) Operating pressure range Operating temperature range Conversion time External clock signal (4) Duty cycle of MCLK Serial Data Clock Symbol VDD Iavg ISC Iss Conditions VDD = 3.0 V Min. 2.2 Typ. 3.0 5 1 Max 3.6 Unit V µA mA µA µA mbar abs. °C ms Hz % kHz MCLK=32768Hz p Ta Tconv MCLK SCLK MCLK=32768Hz 30000 40/60 32768 50/50 300 -10 +25 3.5 0.5 1100 +60 35 35000 60/40 500 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 MS5534. 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 MS5534 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. 5. Reliable operation requires protection of the pressure sensor from direct contact with light. 6. Power supply pins (VDD, GND) must be decoupled with a tantalum (47µF) capacitor placed close to the module. DA5534_022.doc ECN493 July 17th, 2002 3 ELECTRICAL CHARACTERISTICS Digital inputs (T=-40°C .. 60°C) Parameter Input High Voltage Input Low Voltage Signal Rise Time Signal Fall Time Symbol VIH VIL tR tf Conditions VDD = 2.2…3.6V VDD = 2.2…3.6 V Min 80% VDD 0% VDD Typ Max 100% VDD 20% VDD Unit V V ns ns 200 200 Digital outputs (T=-40°C .. 60°C, VDD = 2.2V..3.6V) Parameter Output High Voltage Output Low Voltage Signal Rise Time Signal Fall Time AD-converter Symbol VOH VOL tr tf Conditions ISource = 0.6 mA ISink = 0.6 mA Min 75% VDD 0% VDD Typ Max 100% VDD 20% VDD Unit V V ns ns 200 200 (T=25°C, VDD =3.0V) Parameter Resolution (1) Conversion Time Accuracy (2) Symbol Conditions Min Typ 15 Max Unit Bit MCLK=32768Hz 2 35 7 ms LSB Notes: 7. The ADC output range is from 5,000 counts to 37,000 counts, thus providing a 16-Bit output word. 8. Accuracy limited by the non-linearity of the ADC. DA5534_022.doc ECN493 July 17th, 2002 4 PRESSURE OUTPUT CHARACTERISTICS With the calibration data provided by the MS5534 system (stored in the interface IC) the following characteristics can be achieved: Parameter Resolution Absolute Pressure Accuracy Relative Pressure Accuracy Maximum Error over Temperature Long-term Stability Maximum Error over Supply Voltage Conditions p = 750 …1100mbar Ta = 25°C p = 750 …1100mbar Ta = 25°C Ta = -10…+60°C p = const. 12 month VDD = 2.2…3.6V -1.5 Min -1.5 -0.5 -1 -1 -1 0 +1.5 Typ 0.1 Max +1.5 +0.5 +1 +6 Unit mbar mbar mbar mbar mbar mbar mbar/V Note 1 2 3 4 5 6 Notes: 1. A stable pressure reading of the given resolution requires to take the average of 2 to 4 subsequent pressure values due to noise of the ADC. A better resolution can be obtained with more averaging. 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. W ith the second-order temperature compensation as described in Section "Calculation of pressure using compensation coefficients C1 to C5". 5. W ith the first-order temperature compensation as described in Section "Calculation of pressure using compensation coefficients C1 to C5". 6. 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 Resolution Accuracy Maximum Error over Supply Voltage at reference temperature VDD = 2.2…3.6V Conditions Min 0.005 -0.8 -0.08 Typ Max 0.015 0.8 + 0.08 Unit °C °C °C/V Notes: 1. Refer to the paragraph second-order temperature compensation in the section ‘FUNCTION’ DA5534_022.doc ECN493 July 17th, 2002 5 TYPICAL PERFORMANCE CURVES ADC-value vs Pressure (typical) 20000 19000 18000 17000 ADC-value (LSB) 16000 15000 14000 13000 12000 11000 10000 1000 1100 300 400 500 600 700 800 900 Temp. -10°C Temp.+25°C Temp.+60°C Pressure (m bar) ADC-value D2 vs Temperature (typical) 30000 29000 28000 27000 ADC-value (LSB) 26000 25000 24000 23000 22000 21000 20000 -10 0 10 20 30 40 50 60 Temperature (°C) DA5534_022.doc ECN493 July 17th, 2002 6 Absolute pressure accuracy after calibration (typical) 3.5 3 2.5 Linearity error (mbar) 2 1.5 1 0.5 0 -0.5 -1 -1.5 300 +25°C -10°C (standard calculation) - 10°C (2nd order temperature compensation) +60°C 400 500 600 700 800 900 1000 1100 Pressure (m bar) Accuracy vs temperature (typical) 4 3 2 Temperature Error (°C) 1 0 -1 -2 -3 -4 -10 4 3 2 1 0 -1 -2 -3 -4 0 10 20 30 40 50 60 Temperature (°C) Temperature Error (w ith 2nd order calculation) Pressure Error (mbar) Pressure Error (2nd order temperature compensation) Temperature Error (standard calculation) Pressure Error (standard compensation) DA5534_022.doc ECN493 July 17th, 2002 7 Pressure error vs supply voltage (typical) 0.4 0.3 0.2 Pressure error (mbar) 0.1 0 2.2 -0.1 -0.2 -0.3 -0.4 Voltage (V) 2.4 2.6 2.8 3 3.2 3.4 3.6 Press. 300mbar Press. 700mbar Press. 1100mbar Temperature error (25°C) vs supply voltage (typical) 0.15 0.1 Temperature error (°C) 0.05 0 2.2 -0.05 2.4 2.6 2.8 3 3.2 3.4 3.6 -0.1 -0.15 Voltage (V) DA5534_022.doc ECN493 July 17th, 2002 8 FUNCTION General The MS5534 consists of a piezoresistive sensor and a sensor interface IC. The main function of the MS5534 is to convert the uncompensated analog 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. 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 MS5534. 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”. Measurement principle 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. The A/D converter has been optimized to work in the linear range (numeric values in range [5,000:37,000]). DA5534_022.doc ECN493 July 17th, 2002 9 Start System initialisation Read calibration data (factory calibrated) from PROM of MS5534 Word1, Word2, Word3 and Word4 (4x16 Bit) Basic equations: Example: Word1 = 50426 Word2 = 9504 Word3 = 48029 Word4 = 55028 Convert calibration data into coefficients: (see bit pattern of Word1-Word4) 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 = 25213 C2 = 1908 C3 = 859 C4 = 750 C5 = 148 C6 = 32 Pressure and temperature measurement Read digital pressure value from MS5534A D1 (16 Bit) D1 = 17000 Read digital temperature value from MS5534A D2 (16 Bit) D2 = 22500 Calculate calibration temperature UT1=8*C5+20224 Calculate actual temperature Difference between actual temperature and reference temperature: dT(D2) = D2 - Tref TEMP(D2)=20°+dT(D2)*TEMPSENS dT = 1092 dT = D2 - UT1 Actual temperature in °C: TEMP = (200 + dT*(C6+50)/2 )/10 10 TEMP = 287 = 28.7 °C Calculate temperature compensated pressure Offset at actual temperature: OFF(D2)=OFFT1+TCO*dT(D2) SENS(D2)=SENST1+TCS*dT(D2) OFF = C2*4 + ((C4-512)*dT)/212 Sensitivity at actual temperature: OFF = 7695 SENS = 50705 X = 22732 SENS = C1 + (C3*dT)/210 + 24576 X = (SENS * (D1-7168))/214 - OFF Temperature compensated pressure: P = X*100/25 + 250*100 (0.01mbar resolution) P = X*10/25 + 250*10 (0.1mbar resolution) P(D1,D2)=D1*SENS(D2)-OFF(D2) P = 96037 = 960.37 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 0.1mbar resolution, it is recommended to display the average of 8 subsequent pressure values. DA5534_022.doc ECN493 July 17th, 2002 10 C1 (15 Bit) C5/I 1 Bit Word 1 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB10 C5/II (10 Bit) Word 2 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB5 DB4 C6 (6 Bit) DB3 DB2 DB1 DB0 C4 (10 Bit) Word 3 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB11 DB10 C2/I (6 Bit) DB9 DB8 DB7 DB6 C3 (10 Bit) Word 4 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 DB5 DB4 C2/II (6-Bit) DB3 DB2 DB1 DB0 Fig. 4: Arrangement (Bit-pattern) of calibration data in Word1 to Word4. Second-order temperature compensation In order to obtain full 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 the second-order temperature calculation for D2