MOTOROLA Freescale Semiconductor, Inc. SEMICONDUCTOR APPLICATION NOTE ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 Order this document by AN1652/D AN1652 ASB202 Ċ MPX2000 Series Sensor Module Prepared by: Bill Lucas and Warren Schultz ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 Freescale Semiconductor, Inc... A plug–in module that is part of a systems development tool set for pressure sensors is presented here. It provides an analog signal from an MPX2000 series sensor to a Motorola Sensor Development Controller, or can be used stand alone to provide power and signal conditioning for the sensor. PLUG–IN MODULE DESCRIPTION A summary of information for using systems development plug–in module ASB202 includes the schematic in Figure 2, connector pinout in Figure 3, a pin by pin description of functionality, specs in Tables 1–3, and a parts list in Table 4. Figure 4 in the Applications section provides a quick reference for making connections. A discussion of the design appears under the heading Design Considerations. Function The plug–in module shown in Figure 1 is designed to supply pressure and temperature inputs to a sensor development controller. The sensor output is amplified, level shifted, filtered, and converted to a single ended signal that fits within a zero to 5 volt window. Connections are made through a DB–9 connector, which allows this board to be plugged directly into its controller. If physical separation is desired, a standard 9 wire straight–through serial cable can be inserted between the two boards. Alternately, connections for B+, 5 volts, ground, and the output signal can be made through screw terminals at the top of the board. A socket for sensor connections makes changing from one pressure range to another relatively easy. Figure 1. ASB202 — MPX2000 Series Sensor Module REV 1 Motorola Sensor Device Data Motorola, Inc. 1998 For More Information On This Product, Go to: www.freescale.com 1 Freescale Semiconductor, Inc. AN1652 ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 JT1 B+ JT2 2 +5 JT3 R5 300 VS1 JT4 2 R6 300 2 D1 CNTL JT5 1 D2 +5 D3 RANGE C2 0.01 mF TP3 U3B + 5 1 C1 0.33 mF 1 1N914 C4 0.1 mF RT1 10 k 2 1 KGND R8 1.2 k D4 6 7 – B+ MC33272 JT6 GND R11 R12 2.0 k 1% 2.0 k 1% U1 MPX2010 ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 Freescale Semiconductor, Inc... 3 P1 TP2 5 9 4 8 3 7 2 6 1 R9 2.0 k 1% 3 VS2 2 R7 10 k 1% R10 499 1% 2 + B+ U3A + 1 – 4 GND 1 3 2 – GND MC33272 J1 U2A + 5 1 6 – MC33272 U2B + 7 TP1 – MC33272 R13 R1 R2 R3 R4 390 8.06 k 1% 102 1% 1.02 k 1% 80.6 k 1% RG1 RG2 C3 OPEN OPEN 0.001 mF VS1 DB9 Figure 2. Schematic Electrical Characteristics Unless otherwise specified, the electrical characteristics in Tables 1, 2, & 3, apply to operation at 25 degrees Celsius, B+ = 12.0 volts, and a +5 volt input of 5.00 volts. The values in Tables 2 and 3 are nominal values. Table 1. Electrical Characteristics Characteristic Symbol Min Typ Max Units +5 B+ 4.75 11.6 5.0 12 5.25 15.8 Volts Volts Pressure Sensor Output Voltage — Zero Pressure — Full Scale (MPX2010) — Full Scale (MPX2050–MPX2700) VS1 — — — — — — 1.0 3.0 4.2 — — — Volt Volts Volts Temp Sensor Output Voltage VS2 — 2.5 — Volts Quiescent Current ICC — 25 — mA DC Supply Voltage +5 B+ 2 For More Information On This Product, Go to: www.freescale.com Motorola Sensor Device Data Freescale Semiconductor, Inc. AN1652 ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 Table 2. VS1 Versus Sensor Type Full Scale Pressure (kPa) Sensitivity (mV/kPa) Zero Pressure Offset (Volts) Full Scale Output Voltage (Volts) Full Scale Span (Volts) 10 200 1.0 3.0 2.0 MPX2050 50 64 1.0 4.2 3.2 MPX2100* 100 32 1.0 4.2 3.2 MPX2200 200 16 1.0 4.2 3.2 Sensor MPX2010* *Included with ASB202 kit ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 Freescale Semiconductor, Inc... Table 3. VS2 Versus Temperature Temperature °C RT Ohms VS2 Volts Temperature °C RT Ohms VS2 Volts 0 32773 1.17 40 5323 3.26 5 25456 1.41 45 4365 3.48 10 19932 1.67 50 3599 3.68 15 15725 1.94 55 2983 3.85 20 12497 2.22 60 2486 4.00 25 10000 2.50 65 2082 4.14 30 8055 2.77 70 1753 4.25 35 6528 3.03 75 1482 4.35 Content Pin by Pin Description Board contents are described by the following parts list and the schematic in Figure 2. A pin by pin circuit description follows in the next section. Inputs and outputs are grouped into two connectors. A DB–9 connector provides a plug–in feature. If this connector is used, no other connections are necessary. Alternately, power, ground, and output connections can be made through screw terminals at the top of the board. The screw terminals and the DB–9 are wired in parallel. DB–9 connector pinouts are shown in Figure 3. Table 4. Parts List Item Quantity Reference Part 1 1 C1 .33 µF 2 1 C2 .01 µF 3 1 C3 .001 µF 4 1 C4 .1 µF 5 3 D1,D2,D3 LED (RED) 6 1 D4 IN914 7 1 P1 DB9 8 1 RT1 10K Thermistor 9 1 R1 8.06K 1% 10 1 R2 102 1% 11 1 R3 1.02K 1% 12 1 R4 80.6K 1% 13 2 R5,R6 300 14 1 R7 10K 1% 15 1 R8 1.2K 16 3 R9,R11,R12 2.00K 1% 17 1 R10 499 1% 18 1 R13 390 19 1 U1 MPX2010 20 2 U2,U3 MC33272 Motorola Sensor Device Data 5 9 4 8 3 7 2 6 1 +5 B+ VS2 GND VS1 OPEN KGND CNTL GND Figure 3. DB–9 Pinout DB–9 Connector B+ : Power for the sensor and op amps is supplied through pin 9 on the DB–9 connector. This voltage is labeled B+. It is specified from 11.6 VDC min to 15.8 VDC max. +5: 5 volt power is supplied through pin 5. It is specified from 4.75 VDC min to 5.25 VDC max. GND: The ground connection is on pin one. It connects the sensor’s analog ground to the controller’s digital ground. For More Information On This Product, Go to: www.freescale.com 3 Freescale Semiconductor, Inc. AN1652 ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 KGND: An additional ground connection, labeled KGND, is made on pin 2. As shipped, KGND is tied to GND via jumper J1. If J1 is opened, KGND provides a separate signal ground return that does not carry the op amp and pressures sensor bias currents. This feature can be helpful if a cable is used between the sensor module and its controller. VS2: A temperature dependent output signal is connected to pin 4. It is derived from a thermistor and has a nominal output voltage of 2.5 volts at 25 degrees C. The thermistor’s output is a function of both ambient air temperature, and temperature rise on the board that is conducted through the leads. It will typically read several degrees higher than the temperature of still ambient air. ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 Freescale Semiconductor, Inc... VS1: The pressure sensor output signal, VS1, is connected to pin 3. It is the output of a two op amp discrete instrumentation amplifier that has pressure sensor U1 as its input. Nominal output voltage is 1.0 volt at zero pressure and 3.0 volts at full scale with an MPX2010 sensor. With all of the other MPX2000 series sensors, nominal output voltage is 1.0 volts at zero pressure and 4.2 volts at full scale. CNTL: A control signal is supplied on pin 6. It is normally high, and switches low to light the RANGE light when the sensor’s full scale pressure is exceeded. With code modifications, the pressure at which this transition occurs can be changed, and the signal used to control an external device. Board Code: A board code that lets the controller know that this is an MPX2000 series module is supplied with a ground on pin 7 and an open on pin 8. GND B+ Screw Terminals Connections for B+, +5, VS1, CNTL, KGND, & GND are wired in parallel with the DB–9 connector. As shipped, KGND and GND are tied together with Jumper J1. Test Points TP1–TP3, & GND Test points TP1, TP2, & TP3 provide access to output and bias signals. TP1 is connected to the pressure output signal. TP2 is connected to the thermistor output signal. The sensor’s 10 volt bias voltage, supplied from op amp U3B, appears on TP3. A test point for ground is also provided. Indicator Lights B+ : The B+ light is provided to indicate the presence of the B+ power supply. +5: The +5 light is provided to indicate the presence of 5 volt power. RANGE: The RANGE indicator light turns on when the sensor’s full scale pressure range is exceeded. APPLICATION EXAMPLE An application example shown in Figure 4 illustrates system connections to an ASB200 sensor development controller and a pressure source. This arrangement can be run stand alone, or the ASB200 can be connected to an MMDS or MMEVS system for code development. The two boards are designed such that the DB–9 connectors plug into each other. Once they are plugged in, it is only a matter of connecting a power supply and a pressure source to get a system up and running. If physical separation between the sensor location and the controller is desired, a standard 9 wire straight–through serial cable can be used between the two boards. Measuring different pressure ranges is facilitated by using a socket for the sensor that is supplied on the board. 11.6–15.8 VDC LCD MOTOROLA ASB200 NC +5 VS1 CNTL KGND GND MOTOROLA ASB202 PRESSURE (TOP PORT) OR VACUUM (BOTTOM PORT) +5 VS2 VS1 KGND GND SENSOR DEVELOPMENT CONTROLLER 4 Figure 4. Application Example For More Information On This Product, Go to: www.freescale.com Motorola Sensor Device Data Freescale Semiconductor, Inc. ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 AN1652 across R1, generating 5V/8.06K = 620 µA of current. Assuming that the current in R2 is equal to the current in R1, 620 µA X 102 ohms produces a 63.275 mV drop across R2, which adds to the 5.0 volts at pin 2. The output voltage at pin 1 of U2A is, therefore, 5.063275 volts. This puts 5.063275 5.0 volts across R3, producing 63.275mV/1.02K = 62.035 µA. The same current flowing through R4 produces a voltage drop of (62.035 µA)X(80.6K) = 5.0 volts, which sets the output at zero. Substituting a value for VREF other than zero into this calculation reveals that the zero pressure output voltage equals VREF. For this DC output voltage to be independent of the sensor’s common mode voltage it is necessary to satisfy the condition that R1/R2 = R4/R3. DESIGN CONSIDERATIONS When interfacing MPX2000 series pressure sensors to microcomputers, the design challenge is how to take a relatively small DC coupled differential signal and produce a ground referenced output that is suitable for driving A/D inputs. The circuit shown in Figure 2 provides a reference design performing this task. To see how this amplifier works, let’s simplify it in Figure 5, assume that the voltage source labeled VREF is zero, and set the differential input voltage to zero. If the common mode voltage at sensor inputs S+ and S is 5.0 volts, then pin 2 of U2A and pin 6 of U2B are also at 5.0 volts. This puts 5.0 volts * * ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 Freescale Semiconductor, Inc... S+ 3 S– CONSTRAINTS R4/R3 = R1/R2 R4 = 10 k MIN (R3⋅R4)/(R3+R4) = 2 k MAX (R1⋅R2)/(R1+R2) = 2 k MAX R3 ≅ R2 + SENSOR DELTA ZOUT 2 U2A + 5 1 6 – MC33272 VREF U2B + 7 VOUT – MC33272 R1 R2 R3 R4 8.06 k 1% 102 1% 1.02 k 1% 80.6 k 1% COMMON MODE VOLTAGE = VCM C3 0.001 mF DIFFERENTIAL GAIN ≅ R4/R3 + 1 ZERO PRESSURE OFFSET ≅ VREF(R2⋅R4)/(R1⋅R3) – VCM((R2⋅R4)/(R1⋅R3) – 1) Figure 5. Amplifier — Simplified Schematic Signal gain can be determined by assuming a differential output at the sensor and going through the same calculation. To do this let’s assume 100 mV of differential output and VREF = 0. These values put pin 3 of U2A at 4.95 volts, and pin 5 of U2B at 5.05 volts. Therefore, 4.95 volts is applied to R1, generating 614 µA. This current flowing through R2 produces 62.643 mV, placing pin 1 of U2A at 4950 mV + 62.6 mV = 5012.6 mV. The voltage across R3 is then 5050mV 5012.6 mV = 37.4 mV, which produces a current of 37.4 mV/1.02K = 36.6 µA that flows into R4. The output voltage is then 5.05V + (36.6 µA 80.6K) = 8.0 volts. Dividing 8.0 volts by the 100 mV input yields a gain of 80, which provides a 3.2 volt span for 40 mV of full scale sensor output. The foregoing nodal analysis can be summarized by the following two equations, which are first order approximations. Equation (1) assumes that the differential input between S+ and S in Figure 5 is zero, and that VCM is the common mode voltage at S+ and S . * @ * * Motorola Sensor Device Data (1) ZERO PRESSURE OFFSET @ @ * @ @ *1) 1.0(80.6K@102)/(8.06K@1020) *5.0((80.6K@102)/(8.06K@1020) *1) 1.0(8220K/8220K) *5.0((8220K/8220K)*1) = 1.0 * 0 = 1 Volt = VREF (R2 R4)/(R1 R3) VCM((R2 R4)/(R1 R3) = = (2) DIFFERENTIAL GAIN = R4/R3 +1 = (80.6K/1.02K +1) = 79 + 1 = 80 These equations are based upon the same assumptions as the nodal analysis, namely high open loop gain, zero input offset voltage, zero input bias current, and that the resistor values are actual values as opposed to specified values. As is typical in discrete instrumentation amplifiers, the most troublesome assumption is the resistor values. A 1% variation in the ratio (R4 R2)/(R1 R3) causes an error that is 1% of the common mode voltage at the amplifier’s input. @ For More Information On This Product, Go to: www.freescale.com @ 5 AN1652 Freescale Semiconductor, Inc. ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 sensor and interface is +/– 5%, provided that a provision for zero pressure offset calibration is made. CONCLUSION The ASB202 plug–in module is part of a systems development tool set for pressure sensors. It provides pressure and temperature input signals to a Motorola Sensor Development Controller, or can be used stand alone to provide a signal conditioned output from MPX2000 series sensors. ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 Freescale Semiconductor, Inc... Returning to Figure 2, a 1.0 volt VREF is generated by the divider consisting of R9 and R10. This divider is sourced from the same 5 volts as the controller’s A/D converter reference, thereby minimizing power supply tolerance as a source of error. This divider is buffered by U3A in order to preserve the ratio R4/R3 = R1/R2. The power supply to the sensor is nominally 10.0 volts, and is also generated from the 5 volt reference to minimize power supply errors. The resulting 1.0 V to 4.2 V output from pin 7 of U2B is compatible with microprocessor A/D inputs. Over a zero to 75 degree C temperature range combined accuracy for the 6 For More Information On This Product, Go to: www.freescale.com Motorola Sensor Device Data Freescale Semiconductor, Inc. ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 AN1652 ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005 Freescale Semiconductor, Inc... NOTES Motorola Sensor Device Data For More Information On This Product, Go to: www.freescale.com 7 Freescale Semiconductor, Inc. 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