LDE Series Digital low differential pressure sensors FEATURES · Pressure ranges from 25 to 500 Pa (0.1 to 2 inH2O) · Pressure sensor based on thermal micro-flow measurement · High flow impedance → very low flow-through leakage → high immunity to dust and humidity → no loss in sensitivity using long tubing · Calibrated and temperature compensated · Unique offset autozeroing feature ensuring superb long-term stability · Offset accuracy better than 0.2 %FS · Total accuracy better than 0.5 %FS typical · Analog output and digital SPI interface · RoHS and REACH compliant · Quality Management System according to EN ISO 13485 and EN ISO 9001 MEDIA COMPATIBILITY Air and other non-corrosive gases SPECIFICATIONS Maximum ratings Supply voltage VS LDE...3... 2.70 ... 3.60 VDC LDE...6... 4.75 ... 5.25 VDC Output current 1 mA Lead specifications Average preheating temperature gradient 2.5 K/s Soak time ca. 3 min Time above 217 °C 50 s Time above 230 °C 40 s Time above 250 °C 15 s Peak temperature 260 °C Cooling temperature gradient -3.5 K/s Temperature ranges Compensated 0 ... +70 °C Operating -20 ... +80 °C Storage -40 ... +80 °C Humidity limits (non-condensing) 97 %RH 1 Vibration 20 g 2 Mechanical shock 500 g ELECTRICAL CONNECTION3 Top-down view 10 9 8 7 6 Pin 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 Function Reserved VS GND Vout Vout S C LK MOSI MISO /CS Reserved There are three use cases that will change the manner in which the LDE sensor is connected in-circuit. For detailed pin connections see page 11. Specification notes: 1. Sweep 20 to 2000 Hz, 8 min, 4 cycles per axis, MIL-STD-883, Method 2007. 2. 5 shocks, 3 axes, MIL-STD-883E, Method 2002.4. 3. The maximum voltage applied to pin 1 and pins 6 through 10 should not exceed VS+0.3 V. E / 11815 / C 1/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors PRESSURE SENSOR CHARACTERISTICS Part no. Operating pressure LDES025U... 0...25 Pa / 0...0.25 mbar (0.1 inH2O) LDES050U... 0...50 Pa / 0...0.5 mbar (0.2 inH2O) LDES100U... 0...100 Pa / 0...1 mbar (0.4 inH2O) LDES250U... 0...250 Pa / 0...2.5 mbar (1 inH2O) LDES500U... 0...500 Pa / 0...5 mbar (2 inH2O) LDES025B... 0...±25 Pa / 0...±0.25 mbar (±0.1 inH2O) LDES050B... 0...±50 Pa / 0...±0.5 mbar LDES100B... 0...±100 Pa / 0...±1 mbar (±0.4 inH2O) LDES250B... 0...±250 Pa / 0...±2.5 mbar (±1 inH2O) LDES500B... 0...±500 Pa / 0...±5 mbar (±2 inH2O) Proof pressure4 Burst pressure4 2 bar (30 psi) 5 bar (75 psi) (±0.2 inH2O) GAS CORRECTION FACTORS5 Gas type Dry air Oxygen (O2) Nitrogen (N2) Argon (Ar) Carbon dioxide (CO2) Correction factor 1.0 1.07 0.97 0.98 0.56 Specification notes (cont.): 4. The max. common mode pressure is 5 bar. 5. For example with a LDES500... sensor measuring CO2 gas, at full-scale output the actual pressure will be 500 Pa x 0.56 = 280 Pa. ∆Peff = ∆Psensor × gas correction factor E / 11815 / C ∆Peff = True differential pressure ∆Psensor = Differential pressure as indicated by output voltage 2/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors PERFORMANCE CHARACTERISTICS6 LDE...6... (VS=5.0 VDC, TA=20 °C, PAbs=1 bara, calibrated in air, output signals analog and digital are non-ratiometric to VS) all 25 Pa and 50 Pa devices Characteristics Min. Noise level Offset warm-up shift Offset long term stability7 Current consumption (no load)8 Response time (t63) Power-on time Typ. Max. ±0.025 ±0.05 7 5 Unit Pa less than noise ±0.1 8 Pa/year mA ms 25 Digital output Characteristics 9 Scale factor (digital output) Zero pressure offset accuracy10 Span accuracy10, 11 Thermal effects Offset Span Min. 0...25 / 0...±25 Pa 0...50 / 0...±50 Pa 5...55 0...70 5...55 0...70 Typ. 1200 600 ±0.1 ±0.4 Max. Unit counts/Pa %FSS % of reading ±1 ±2 ±0.2 ±0.75 ±0.2 ±0.4 ±1.75 ±2.75 Min. Typ. Max. Unit 0.49 0.50 4.50 ±0.4 0.51 °C °C °C °C %FSS % of reading Analog output (unidirectional devices) Characteristics Zero pressure offset Full scale output Span accuracy10, 11 Thermal effects Offset Span 5...55 0...70 5...55 0...70 ±1.25 ±2 ±0.75 ±15 ±30 ±2 ±2.75 Min. Typ. Max. 2.49 2.50 4.50 0.50 ±0.4 2.51 °C °C °C °C V % of reading mV % of reading Analog output (bidirectional devices) Characteristics Zero pressure offset Output Span accuracy10, 11 Thermal effects at max. specified pressure at min. specified pressure Offset Span E / 11815 / C 5...55 0...70 5...55 0...70 °C °C °C °C ±1.25 ±2 Unit V ±0.75 ±15 ±30 ±2 ±2.75 % of reading mV % of reading 3/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors PERFORMANCE CHARACTERISTICS6 LDE...6... (VS=5.0 VDC, TA=20 °C, PAbs=1 bara, calibrated in air, output signals analog and digital are non-ratiometric to VS) all 100 Pa, 250 Pa and 500 Pa devices Characteristics Min. Noise level Offset warm-up shift Offset long term stability7 Current consumption (no load)8 Response time (t63) Power-on time Typ. Max. ±0.04 ±0.05 7 5 Unit %FS less than noise ±0.1 8 %FSS/year mA ms 25 Digital output Characteristics 9 Scale factor (digital output) Min. 0...100 / 0...±100 Pa 0...250 / 0...±250 Pa 0...500 / 0...±500 Pa 300 120 60 ±0.05 ±0.4 Zero pressure offset accuracy10 Span accuracy10, 11 Thermal effects Offset 5...55 °C 0...70 °C Span 5...55 °C 0...70 °C Analog output (unidirectional devices) Characteristics Zero pressure offset Full scale output Span accuracy10, 11 Thermal effects Offset Span 5...55 0...70 5...55 0...70 Typ. Max. Unit counts/Pa %FSS % of reading ±1 ±2 ±0.1 ±0.75 ±0.1 ±0.2 ±1.75 ±2.75 Min. Typ. Max. Unit 0.49 0.50 4.50 ±0.4 0.51 ±1 ±2 ±0.75 ±10 ±12 ±1.75 ±2.75 Min. Typ. Max. 2.49 2.50 4.50 0.50 ±0.4 2.51 °C °C °C °C %FSS % of reading V % of reading mV % of reading Analog output (bidirectional devices) Characteristics Zero pressure offset Output Span accuracy10, 11 Thermal effects at max. specified pressure at min. specified pressure Offset Span E / 11815 / C 5...55 0...70 5...55 0...70 °C °C °C °C ±1 ±2 Unit V ±0.75 ±10 ±12 ±1.75 ±2.75 % of reading mV % of reading 4/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors PERFORMANCE CHARACTERISTICS6 LDE...3... (VS=3.0 VDC, TA=20 °C, PAbs=1 bara, calibrated in air, output signals analog and digital are non-ratiometric to VS) all 25 Pa and 50 Pa devices Characteristics Min. Noise level Offset warm-up shift Offset long term stability7 Current consumption (no load)8 Response time (t63) Power-on time Typ. Max. ±0.025 ±0.05 14 5 Unit Pa less than noise ±0.1 16 Pa/year mA ms 25 Digital output Characteristics 9 Scale factor (digital output) Zero pressure offset accuracy10 Span accuracy10, 11 Thermal effects Offset Span Min. 0...25 / 0...±25 Pa 0...50 / 0...±50 Pa 5...55 0...70 5...55 0...70 Typ. 1200 600 ±0.1 ±0.4 Max. Unit counts/Pa %FSS % of reading ±1 ±2 ±0.2 ±0.75 ±0.2 ±0.4 ±1.75 ±2.75 Min. Typ. Max. Unit 0.29 0.30 2.70 ±0.4 0.31 °C °C °C °C %FSS % of reading Analog output (unidirectional devices) Characteristics Zero pressure offset Full scale output Span accuracy10, 11 Thermal effects Offset Span 5...55 0...70 5...55 0...70 ±1.25 ±2 ±0.75 ±15 ±30 ±2 ±2.75 Min. Typ. Max. 1.49 1.50 2.70 0.30 ±0.4 1.51 °C °C °C °C V % of reading mV % of reading Analog output (bidirectional devices) Characteristics Zero pressure offset Output Span accuracy10, 11 Thermal effects at max. specified pressure at min. specified pressure Offset Span E / 11815 / C 5...55 0...70 5...55 0...70 °C °C °C °C ±1.25 ±2 Unit V ±0.75 ±15 ±30 ±2 ±2.75 % of reading mV % of reading 5/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors PERFORMANCE CHARACTERISTICS6 LDE...3... (VS=3.0 VDC, TA=20 °C, PAbs=1 bara, calibrated in air, output signals analog and digital are non-ratiometric to VS) all 100 Pa, 250 Pa and 500 Pa devices Characteristics Min. Noise level Offset warm-up shift Offset long term stability7 Current consumption (no load)8 Response time (t63) Power-on time Typ. Max. ±0.04 ±0.05 14 5 Unit %FS less than noise ±0.1 16 %FSS/year mA ms 25 Digital output Characteristics 9 Scale factor (digital output) Min. 0...100 / 0...±100 Pa 0...250 / 0...±250 Pa 0...500 / 0...±500 Pa 300 120 60 ±0.05 ±0.4 Zero pressure offset accuracy10 Span accuracy10, 11 Thermal effects Offset 5...55 °C 0...70 °C Span 5...55 °C 0...70 °C Analog output (unidirectional devices) Characteristics Zero pressure offset Full scale output Span accuracy10, 11 Thermal effects Offset Span 5...55 0...70 5...55 0...70 Typ. Max. Unit counts/Pa %FSS % of reading ±1 ±2 ±0.1 ±0.75 ±0.1 ±0.2 ±1.75 ±2.75 Min. Typ. Max. Unit 0.29 0.30 2.70 ±0.4 0.31 ±1 ±2 ±0.75 ±10 ±12 ±1.75 ±2.75 Min. Typ. Max. 1.49 1.50 2.70 0.30 ±0.4 1.51 °C °C °C °C %FSS % of reading V % of reading mV % of reading Analog output (bidirectional devices) Characteristics Zero pressure offset Output Span accuracy10, 11 Thermal effects at max. specified pressure at min. specified pressure Offset Span E / 11815 / C 5...55 0...70 5...55 0...70 °C °C °C °C ±1 ±2 Unit V ±0.75 ±10 ±12 ±1.75 ±2.75 % of reading mV % of reading 6/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors PERFORMANCE CHARACTERISTICS (cont.) Total accuracy12 Fig. 1: Typical total accuracy plot of 16 LDE 50 Pa sensors @ 25 °C (typical total accuracy better than 0.5 %FS) Offset long term stability Fig. 2: Offset long term stability for LDE 250 Pa sensors after 10 000 hours @ 85°C powered, equivalent to over 43.5 years @ 25 °C (better than ±2 mV / ±0.125 Pa) Specification notes (cont.): 6. The sensor is calibrated with a common mode pressure of 1 bar absolute. Due to the mass flow based measuring principle, variations in absolute common mode pressure need to be compensated according to the following formula: ∆Peff = ∆Psensor × 1 bara Pabs ∆Peff = True differential pressure ∆Psensor = Differential pressure as indicated by output voltage Pabs = Current absolute common mode pressure 7. 8. 9. 10. Figure based on accelerated lifetime test of 10 000 hours at 85 °C biased burn-in. Please contact First Sensor for low power options. The digital output signal is a signed, two's complement integer. Negative pressures will result in a negative output. Zero pressure offset accuracy and span accuracy are uncorrelated uncertainties. They can be added according to the principles of error propagation. 11. Span accuracy below 10 % of full scale is limited by the intrinsic noise of the sensor. 12. Total accuracy is the combined error from offset and span calibration, non-linearity, repeatability and pressure hysteresis. E / 11815 / C 7/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors SPI - SERIAL PERIPHERAL INTERFACE Note: It is important to adhere to the communication protocol in order to avoid damage to the sensor. Introduction The LDE serial interface is a high-speed synchronous data input and output communication port. The serial interface operates using a standard 4-wire SPI bus. The LDE device runs in SPI mode 0, which requires the clock line SCLK to idle low (CPOL = 0), and for data to be sampled on the leading clock edge (CPHA = 0). Figure 5 illustrates this mode of operation. There are, however, some cases where it may be helpful to use 33Ω series resistors at both ends of the SPI lines, as shown in Figure 3. Signal quality may be further improved by the addition of a buffer as shown in Figure 4. These cases include multiple slave devices on the same bus segment, using a master device with limited driving capability and long SPI bus lines. Care should be taken to ensure that the sensor is properly connected to the master microcontroller. Refer to the manufacturer's datasheet for more information regarding physical connections. If these series resistors are used, they must be physically placed as close as possible to the pins of the master and slave devices. Application circuit Signal control The use of pull-up resistors is generally unnecessary for SPI as most master devices are configured for push-pull mode. If pull-up resistors are required for use with 3 V LDE devices, however, they should be greater than 50 kΩ. The serial interface is enabled by asserting /CS low. The serial input clock, SCLK, is gated internally to begin accepting the input data at MOSI, or sending the output data on MISO. When /CS rises, the data clocked into MOSI is loaded into an internal register. MOSI 33 33 MOSI MISO 33 33 MISO SCLK 33 33 SCLK /CS 33 33 /CS 33 33 MOSI 33 33 MISO 33 33 SCLK 33 33 /CS Sensor Fig. 3: Resistors at both ends of the SPI lines MOSI 33 MISO 33 /OE Sensor /OE SCLK 33 /CS 33 /OE /OE Fig. 4: Addition of a buffer E / 11815 / C 8/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors SPI - SERIAL PERIPHERAL INTERFACE (cont.) Note: It is important to adhere to the communication protocol in order to avoid damage to the sensor. Data read When powered on, the sensor begins to continuously measure pressure. To initiate data transfer from the sensor, the following three unique bytes must be written sequentially, MSB first, to the MOSI pin (see Figure 5): Step Hexadecimal Binary Description 1 0x2D B00101101 Poll current pressure measurement 2 0x14 B00010100 Send result to data register 3 0x98 B10011000 Read data register The entire 16 bit content of the LDE register is then read out on the MISO pin, MSB first, by applying 16 successive clock pulses to SCLK with /CS asserted low. Note that the value of the LSB is held at zero for internal signal processing purposes. This is below the noise threshold of the sensor and thus its fixed value does not affect sensor performance and accuracy. Step 1 From the digital sensor output the actual pressure value can be calculated as follows: digital output [counts ] pressure [Pa ] = counts scale factor Pa For example, for a ±250 Pa sensor (LDES250B...) with a scale factor of 120 a digital output of 30 000 counts (7530’h) calculates to a positive pressure of 250 Pa. Similarly, a digital output of -30 000 counts (8AD0’h) calculates to a negative pressure of -250 Pa. Step 2 /CS SCLK (CPOL=0) (CPHA=0) MOSI 0 0 1 0 1 1 0 1 0 0 0 1 0 1 0 0 MISO Step 3 Data from sensor /CS SCLK (CPOL=0) (CPHA=0) MOSI 1 0 0 1 1 0 0 0 MSB MISO 15 14 13 12 11 10 LSB 9 8 7 6 5 4 3 2 1 0 Fig. 5: SPI data transfer E / 11815 / C 9/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors Interface specification Parameter Symbol fECLK External clock frequency External master clock input low time External master clock input high time SCLK setup to falling edge /CS /CS falling edge to SCLK rising edge setup time /CS idle time SCLK falling edge to data valid delay Data valid to SCLK rising edge setup time Data valid to SCLK rising edge hold time SCLK high pulse width SCLK low pulse width /CS rising edge to SCLK rising edge hold time /CS falling edge to output enable /CS rising edge to output disable LDE...6... (5 V supply) Maximum output load capacitance CLOAD VIH VIL VOH Output voltage, logic LOW VOL CLOAD VIH VIL VOH VOL Input voltage, logic HIGH Input voltage, logic LOW Output voltage, logic HIGH Output voltage, logic LOW Min. Min. Max. Typ. 40 40 30 30 1.5 Unit MHz 60 60 %tECLK ns µs 80 30 30 100 100 30 ns 25 25 RLOAD=∞, phase margin >55° 200 0.8×VS RLOAD=∞ RLOAD =2 kΩ RLOAD=∞ RLOAD =2 kΩ Max. 0.2 5 fECLKIN LO tECLK=1/fECLK fECLKIN HI tECLK=1/fECLK tSC tCSS tCSI fCLK=4 MHz tDO CLOAD=15 pF tDS tDH tCH tCL tCSH tDV CLOAD=15 pF tTR CLOAD=15 pF Input voltage, logic HIGH Input voltage, logic LOW Output voltage, logic HIGH LDE...3... (3 V supply)13 Maximum output load capacitance Conditions VCKSEL=0 pF VS+0.3 0.2×VS VS-0.1 VS-0.15 V 0.5 0.2 RLOAD =1 kΩ 15 0.65×VS IO=-20 µA IO=20 µA pF VS+0.3 0.35×VS VS-0.4 V 0.4 Specification notes (cont.): 13. For correct operation of LDE…3... devices, the device driving the SPI bus must have a minimum drive capability of ±2 mA. tCSI /CS tSC tCSS tCL tCSH tCH SCLK tDS tDH MOSI tDV tDO tTR MISO Fig. 5: Timing diagram E / 11815 / C 10/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors OUTLINE DRAWING LDE...E... (SMD, 2 ports same side) 17.70 12.70 ±0.15 5.60 ±0.2 0.25 High pressure port 10 9 8 7 6 3.0 13.85 15.22 18.03 Ø 2.20 17.53 10.70 ±0.15 5.0 6.26 1 2 3 4 5 1.43 5.08 2.54 3.10 ±0.2 0.51 1.27 1.60 ±0.2 5.60 dimensions in mm 2.50 LDE...F... (DIP, 2 ports same side) 17.70 12.70 ±0.15 5.60 ±0.2 High pressure port 10 9 8 7 6 3.0 0.25 14.97 18.03 Ø 2.20 17.53 10.70 ±0.15 5.0 6.26 1 2 3 4 5 7.85 8.95 ±0.5 15.65 16.05 10.16 2.54 0.46 3.10 ±0.2 1.60 ±0.2 5.60 2.50 E / 11815 / C dimensions in mm 11/12 www.first-sensor.com www.sensortechnics.com LDE Series Digital low differential pressure sensors ELECTRICAL CONNECTION (cont.)3 There are three use cases that will change the manner in which the LDE series device is connected in-circuit: Case 1: Reading of pressure measurement as a digital (SPI) signal; Case 2: Reading of pressure measurement as an analog (voltage) signal; and Case 3: Pin-to-pin compatible drop-in replacement for LBA series devices (5 V LDE devices only). The connections for each such use case must be made as indicated below. Connection Pin Function C a se 1 : Digital signal output C a se 2 : Analog signal output 1 2 3 4 5 6 7 8 9 10 Reserved VS GND Vout Vout S C LK MOSI MISO /CS Reserved NC +5 V / +3 V GND NC NC Master device SCLK Master device MOSI Master device MISO Master device (/CS) NC NC +5 V / +3 V GND C a se 3 : LBA drop-in replacement (5 V LDE only) GND +5 V GND High-impedance analog input High-impedance analog input (e.g. op-amp, ADC) (e.g. op-amp, ADC) GND GND GND VS NC GND GND GND GND GND ORDERING INFORMATION Series Pressure range Options LD E S 025 S 050 S 100 Calibration 25 Pa B Bidirectional U Unidirectional 50 P a Housing Output (0.1 inH2O) E SMT, 2 ports 3 non-ratiometric, same side 3 V supply (0.2 inH2O) F DIP, 2 ports same side 6 non-ratiometric, 5 V supply F 6 Grade S High 100 P a (0.4 inH2O) S 250 250 P a (1 inH2O) S 500 500 P a (2 inH2O) Example: LD E S 250 B S First Sensor reserves the right to make changes to any products herein. First Sensor does not assume any liability arising out of the application or use of any product or circuit described herein, neither does it convey any license under its patent rights nor the rights of others. E / 11815 / C 12/12 www.first-sensor.com www.sensortechnics.com