SCA61T

SCA61T Series Data Sheet THE SCA61T INCLINOMETER SERIES The SCA61T Series is a 3D-MEMS-based single axis inclinometer family that provides instrumentation grade performance for leveling applications. Low temperature dependency, high resolution and low noise together with robust sensing element design make the SCA61T ideal choice for leveling instruments. The VTI inclinometers are insensitive to vibration, due to their over damped sensing elements and can withstand mechanical shocks of 20000 g. Features • • • • • • • Measuring ranges ±30° SCA61T-FAHH1G and ± 90° SCA61T-FA1H1G 0.0025° resolution (10 Hz BW, analog output) Sensing element controlled over damped frequency response (-3dB 18Hz) Robust design, high shock durability (20000g) Excellent stability over temperature and time Single +5 V supply Ratiometric analog voltage outputs • • Digital SPI inclination and temperature output Comprehensive failure detection features o True self test by deflecting the sensing elements’ proof mass by electrostatic force. o Continuous sensing element interconnection failure check. o Continuous memory parity check. • RoHS compliant • Compatible with Pb-free reflow solder process Applications • • Platform leveling and stabilization Leveling instruments 8 VDD • Acceleration and motion measurement S ensing element Signal conditioning and filtering A/D conversion 7 OUT 6 ST Self test 1 EEPROM calibration memory Temperature Sensor SPI interface 1 SCK 2 MISO 3 MOSI 5 CSB 4 GND Figure 1. Functional block diagram VTI Technologies Oy www.vti.fi Subject to changes Doc. nr. 8261900 1/18 Rev.A SCA61T Series TABLE OF CONTENTS The SCA61T Inclinometer Series.............................................................................................1 Features................................................................................................................................................1 Applications .........................................................................................................................................1 Table of Contents .....................................................................................................................2 1 Electrical Specifications .....................................................................................................3 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Absolute Maximum Ratings......................................................................................................3 Performance Characteristics ....................................................................................................3 Electrical Characteristics ..........................................................................................................4 SPI Interface DC Characteristics ..............................................................................................4 SPI Interface AC Characteristics ..............................................................................................4 SPI Interface Timing Specifications .........................................................................................5 Electrical Connection ................................................................................................................6 Typical Performance Characteristics.......................................................................................6 Additional External Compensation ..........................................................................................7 2 Functional Description .......................................................................................................9 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Measuring Directions ................................................................................................................9 Voltage to Angle Conversion....................................................................................................9 Ratiometric Output ....................................................................................................................9 SPI Serial Interface ..................................................................................................................10 Digital Output to Angle Conversion .......................................................................................12 Self Test and Failure Detection Modes ..................................................................................13 Temperature Measurement .....................................................................................................14 3 Application Information ....................................................................................................15 3.1 3.2 Recommended Circuit Diagrams and Printed Circuit Board Layouts ................................15 Recommended Printed Circuit Board Footprint ...................................................................16 4 Mechanical Specifications and Reflow Soldering ..........................................................16 4.1 4.2 Mechanical Specifications (Reference only) .........................................................................16 Reflow Soldering......................................................................................................................17 5 Document Change Control...............................................................................................18 6 Contact Information ..........................................................................................................18 VTI Technologies Oy www.vti.fi Subject to changes Doc. nr. 8261900 2/18 Rev.A SCA61T Series 1 Electrical Specifications The SCA61T product family comprises two versions, the SCA61T-FAHH1G and the SCA61TFA1H1G, that differ in measurement range. The product version specific performance specifications are listed in the following table below. All other specifications are common to both versions. Vdd=5.00V and ambient temperature unless otherwise specified. 1.1 Absolute Maximum Ratings Supply voltage (VDD) Voltage at input / output pins Storage temperature Operating temperature Mechanical shock -0.3 V to +5.5V -0.3V to (VDD + 0.3V) -55°C to +125°C -40°C to +125°C Drop from 1 meter on a concrete surface (20000g). Powered or non-powered 1.2 Performance Characteristics Parameter Measuring range Frequency response Offset (Output at 0g) Offset calibration error Offset Digital Output Sensitivity Sensitivity calibration error Sensitivity Digital Output Offset temperature dependency Sensitivity temperature dependency Typical non-linearity Digital output resolution Output noise density Analog output resolution Ratiometric error Cross-axis sensitivity Long term Stability (4 Note 1. Note 2. Note 3. Note 4. Condition Nominal –3dB LP (1 Ratiometric output between 0…1° (2 SCA61TFAHH1G ±30 ±0.5 8-28 Vdd/2 ±0.11 1024 4 70 ±0.5 1638 ±0.008 ±0.86 ±0.014 -2.5...+1 ±0.11 11 0.035 0.0008 0.0025 ±1 4 Figure 8. VOUT =2.5V > VOUT The measuring direction of the SCA61T 2.2 Voltage to Angle Conversion Analog output can be transferred to angle using the following equation for conversion: α = arcsin⎜ ⎜ ⎛ Vout − Offset ⎞ ⎟ ⎟ ⎝ Sensitivity ⎠ where: Offset = output of the device at 0° inclination position, Sensitivity is the sensitivity of the device and VDout is the output of SCA61T. The nominal offset is 2.5 V and the sensitivity is 4 V/g with SCA61T-FAHH1G and 2 V/g with SCA61T-FA1H1G. Angles close to 0° inclination can be estimated quite accurately with straight line conversion but for best possible accuracy arcsine conversion is recommended to be used. The following table shows the angle measurement error if straight line conversion is used. Straight line conversion equation: α= Vout − Offset Sensitivity Where: Sensitivity = 70mV/° with SCA61T-FAHH1G or Sensitivity= 35mV/° with SCA61T-FA1H1G Tilt angle [°] 0 1 2 3 4 5 10 15 30 Straight line conversion error [°] 0 0.0027 0.0058 0.0094 0.0140 0.0198 0.0787 0.2185 1.668 2.3 Ratiometric Output Ratiometric output means that zero offset point and sensitivity of the sensor are proportional to the supply voltage. If the SCA61T supply voltage is fluctuating, the SCA61T output will also vary. When the same reference voltage for both the SCA61T sensor and the measuring part (A/Dconverter) is used, the error caused by reference voltage variation is automatically compensated for. VTI Technologies Oy www.vti.fi Subject to changes Doc. nr. 8261900 9/18 Rev.A SCA61T Series 2.4 SPI Serial Interface A Serial Peripheral Interface (SPI) system consists of one master device and one or more slave devices. The master is defined as a micro controller providing the SPI clock and the slave as any integrated circuit receiving the SPI clock from the master. The ASIC in VTI Technologies’ products always operates as a slave device in master-slave operation mode. The SPI has a 4-wire synchronous serial interface. Data communication is enabled with a low active Slave Select or Chip Select wire (CSB). Data is transmitted with a 3-wire interface consisting of wires for serial data input (MOSI), serial data output (MISO) and serial clock (SCK). MASTER MICROCONTROLLER DATA OUT (MOSI) DATA IN (MISO) SERIAL CLOCK (SCK) SS0 SS1 SS2 SS3 SI SO SCK CS SI SO SCK CS SI SO SCK CS SLAVE SI SO SCK CS Figure 9. Typical SPI connection The SPI interface in VTI products is designed to support any micro controller that uses an SPI bus. Communication can be carried out by a software or hardware based SPI. Please note that in the case of a hardware based SPI, the received acceleration data is 11 bits. The data transfer uses the following 4-wire interface: MOSI MISO SCK CSB master out slave in master in slave out serial clock chip select (low active) µP → SCA61T SCA61T → µP µP → SCA61T µP → SCA61T Each transmission starts with a falling edge of CSB and ends with the rising edge. During transmission, commands and data are controlled by SCK and CSB according to the following rules: • • • • • • • commands and data are shifted; MSB first, LSB last each output data/status bits are shifted out on the falling edge of SCK (MISO line) each bit is sampled on the rising edge of SCK (MOSI line) after the device is selected with the falling edge of CSB, an 8-bit command is received. The command defines the operations to be performed the rising edge of CSB ends all data transfer and resets internal counter and command register if an invalid command is received, no data is shifted into the chip and the MISO remains in high impedance state until the falling edge of CSB. This reinitializes the serial communication. data transfer to MOSI continues immediately after receiving the command in all cases where data is to be written to SCA61T’s internal registers Subject to changes Doc. nr. 8261900 10/18 Rev.A VTI Technologies Oy www.vti.fi SCA61T Series • • • data transfer out from MISO starts with the falling edge of SCK immediately after the last bit of the SPI command is sampled in on the rising edge of SCK maximum SPI clock frequency is 500kHz maximum data transfer speed for RDAX is 5300 samples per sec / channel The SPI command can be either an individual command or a combination of command and data. In the case of combined command and data, the input data follows uninterruptedly the SPI command and the output data is shifted out parallel with the input data. The SPI interface uses an 8-bit instruction (or command) register. The list of commands is given in Table below. Command Name MEAS RWTR RDSR RLOAD STX RDAX Command Format 00000000 00001000 00001010 00001011 00001110 00010000 Description: Measure mode (normal operation mode after power on) Read and write temperature data register Read status register Reload NV data to memory output register Activate Self test for X-channel Read X-channel acceleration through SPI Measure mode (MEAS) is standard operation mode after power-up. During normal operation, the MEAS command is the exit command from Self test. Read temperature data register (RWTR) reads temperature data register during normal operation without effecting the operation. Temperature data register is updated every 150 µs. The load operation is disabled whenever the CSB signal is low, hence CSB must stay high at least 150 µs prior the RWTR command in order to guarantee correct data. The data transfer is presented in Figure below. The data is transferred MSB first. In normal operation, it does not matter what data is written into temperature data register during the RWTR command and hence writing all zeros is recommended. C SB 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 SC K C O M M AN D D A T A IN 7 6 5 4 3 2 1 0 M OSI H IG H IM PED AN C E D A TA O U T 7 6 5 4 3 2 1 0 M ISO Figure 10. Command and 8 bit temperature data transmission over the SPI Self test for X-channel (STX) activates the self test function for the X-channel (Channel 1). The Internal charge pump is activated and a high voltage is applied to the X-channel acceleration sensor element electrode. This causes the electrostatic force that deflects the beam of the sensing element and simulates the acceleration to the positive direction. The self-test is de-activated by giving the MEAS command. Read X-channel acceleration (RDAX) accesses the AD converted X-channel acceleration signal stored in acceleration data register X. During normal operation, acceleration data registers are reloaded every 150 µs. The load operation is disabled whenever the CSB signal is low, hence CSB must stay high at least 150 µs prior the RDAX command in order to guarantee correct data. Data output is an 11-bit digital word that is fed out MSB first and LSB last. VTI Technologies Oy www.vti.fi Subject to changes Doc. nr. 8261900 11/18 Rev.A SCA61T Series CSB 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 SCK COM M AND M OSI DATA OUT 10 9 8 7 6 5 4 3 2 1 0 H IG H IM P E D A N C E M IS O Figure 11. Command and 11 bit acceleration data transmission over the SPI 2.5 Digital Output to Angle Conversion The acceleration measurement results in RDAX data register are in 11 bit digital word format. The data range is from 0 to 2048. The nominal content of RDAX data register in zero angle position is: Binary: 100 0000 0000 Decimal: 1024 The transfer function from differential digital output to angle can be presented as α = arcsin⎜ ⎜ where; Dout ⎛ Dout [LSB] − Dout@ 0° [LSB] ⎞ ⎟ ⎟ Sens [LSB/g] ⎝ ⎠ digital output (RDAX) digital offset value, nominal value = 1024 angle sensitivity of the device. (SCA61T-FAHH1G: 1638, SCA61T-FA1H1G: 819) α Dout@0° Sens As an example following table contains data register values and calculated differential digital output values with -5, -1 0, 1 and 5 degree tilt angles. Angle [°] -5 -1 0 1 5 Acceleration [mg] -87.16 -17.45 0 17.45 87.16 RDAX (SCA61TFAHH1G) dec: 881 bin: 011 0111 0001 dec: 995 bin: 011 1110 0011 dec: 1024 bin: 100 0000 0000 dec: 1053 bin: 100 0001 1101 dec: 1167 bin: 100 1000 1111 RDAX (SCA61TFA1H1G) dec: 953 bin: 011 1011 1001 dec: 1010 bin: 011 1111 0010 dec: 1024 bin: 100 0000 0000 dec: 1038 bin: 100 0000 1110 dec: 1095 bin: 100 0100 0111 VTI Technologies Oy www.vti.fi Subject to changes Doc. nr. 8261900 12/18 Rev.A SCA61T Series 2.6 Self Test and Failure Detection Modes To ensure reliable measurement results the SCA61T has continuous interconnection failure and calibration memory validity detection. A detected failure forces the output signal close to power supply ground or VDD level, outside the normal output range. The normal output ranges are: analog 0.25-4.75 V (@Vdd=5V) and SPI 102...1945 counts. The calibration memory validity is verified by continuously running parity check for the control register memory content. In the case where a parity error is detected the control register is automatically re-loaded from the EEPROM. If a new parity error is detected after re-loading data both analog output voltage is forced to go close to ground level (