LM9044 LM9044 Lambda Sensor Interface Amplifier Literature Number: SNOSBP4C LM9044 Lambda Sensor Interface Amplifier General Description The LM9044 is a precision differential amplifier specifically designed for operation in the automotive environment. Gain accuracy is guaranteed over the entire automotive temperature range (-40C to +125C) and is factory trimmed after package assembly. The input circuitry has been specifically designed to reject common-mode signals as much as 3V below ground without the need for a negative voltage supply. This facilitates the use of sensors which are grounded at the engine block while the LM9044 itself is grounded at chassis potential. An external capacitor on the RF pin sets the maximum operating frequency of the amplifier, thereby filtering high frequency transients. Both inputs are protected against accidental shorting to the battery and against load dump transients. The input impedance is typically 1.2 M. The output op amp is capable of driving capacitive loads and is fully protected. Also, internal circuitry has been provided to detect open circuit conditions on either or both inputs and force the output to a "home" position (a ratio of the external reference voltage). Features Normal circuit operation guaranteed with inputs up to 3V below ground on a single supply. Gain factory trimmed and guaranteed over temperature (3% of full-scale from -40C to +125C) Low power consumption (typically 1 mA) Fully protected inputs Input open circuit detection Operation guaranteed over the entire automotive temperature range (-40C to +125C) Typical Application 674415 (c) 2009 National Semiconductor Corporation 6744 www.national.com LM9044 Lambda Sensor Interface Amplifier March 3, 2009 LM9044 Connection Diagram Plastic Chip Carrier Package 674406 *Pins 1, 3, 4, 6, 8, 9, 10, 11, 13, 14, 16, 18, 19 are trim pins and should be left floating. Top View Order Number LM9044V See NS Package Number V20A www.national.com 2 If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VCC Supply Voltage (RVCC = 15 k) VREF Supply Voltage DC Input Voltage (Either input)(Note 3) Input Transients (Note 2) Power Dissipation see (Note 8) Electrical Characteristics Parameter Differential Voltage Gain Gain Error (Note 7) Differential Input Resistance Non-Inverting Input Bias Current 60V -0.3V to +6V -3V to +16V 60V 1350 mW VCC = 12V, VREF = 5V, -40C TA 125C unless otherwise noted (Note 4) Conditions (Note 5) Units Min Typ Max Min Typ Max VDIFF = 0.5, -1V VCM +1V 4.41 4.50 4.59 - - - V/V VDIFF = 0.5, -3V VCM +1V - - - 4.36 4.50 4.64 V/V 0 VDIFF 1V, -1V VCM +1V -2 0 2 - - - %/FS 0 VDIFF 1V, -3 VCM +1V - - - -3 0 3 %/FS 0 VDIFF 1V, -1V VCM +1V 0.95 1.20 3.00 - - - M 0 VDIFF 1V, -3 VCM +1V - - - 0.70 1.20 4.00 M 0 VDIFF 1V, -1 VCM +1V - 0.38 0.65 - - - A 0 VDIFF 1V, -3 VCM +1V - - - - 0.38 1.5 A 0 VDIFF 1V, -1 VCM +1V -25 -65 -100 - - - A 0 VDIFF 1V, -3 VCM +1V - - - - -45 -150 A VCC Supply Current VCC = 12V, RVCC = 15k - 300 500 - - - A VREF Supply Current 4.75V VREF 5.5V - 0.5 1.0 - - - mA -1 - 1 -3 - 1 V 50 60 - - - - dB 0.371 0.397 0.423 - - - xVREF Inverting Input Bias Current Common-Mode Voltage Range (Note 6) DC Common-Mode Rejection Ratio Input Referred -1V VCM +1V, VDIFF = 0.5V One or Both Inputs Open Open Circuit Output Voltage -1V VCM +1V -3V VCM +1V - - - 0.365 0.397 0.439 xVREF Short Circuit Output Current Output Grounded 1.0 2.7 5.0 - - - mA VCC Power Supply Rejection Ratio VCC = 12V, RVCC = 15k VDIFF = 0.5V 50 65 - - - - dB VREF Power Supply Rejection Ratio VREF = 5 VDC VDIFF = 0.5V 60 74 - - - - dB Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Note 2: This test is performed with a 1000 source impedance. Note 3: With a 100 series resistor on each input pin. Note 4: These parameters are guaranteed and 100% production tested. Note 5: These parameters will be guaranteed but not 100% production tested. Note 6: The LM9044 has been designed to common-mode to -3V, but production testing is only performed at 1V. Note 7: Gain error is given as a percent of full-scale. Full-scale is defined as 1V at the input and 4.5V at the output. Note 8: For operation in ambient temperatures above 25C the device must be derated based on a maximum junction temperature of 150C and a thermal resistance of 93C/W junction to ambient. 3 www.national.com LM9044 Output Short Circuit Duration Indefinite Operating Temperature Range -40C to +125C Storage Temperature Range -65C to +150C Soldering Information Plastic Chip Carrier Package Vapor Phase (60 seconds) 215C Infrared (15 seconds) 220C See AN-450 "Surface Mounting Methods and Their Effect on Product Reliability" for other methods of soldering surface devices. Absolute Maximum Ratings (Note 1) LM9044 Typical Performance Characteristics Non-Inverting Input Bias Current vs Temperature Inverting Input Bias Current vs Temperature 674402 674407 VREF Supply Current vs Temperature VCC Supply Current vs Temperature 674408 674409 Differential Gain vs Temperature Short Circuit Output Current vs Temperature 674403 674410 www.national.com 4 LM9044 Voltage Gain vs Frequency CMRR vs Frequency 674411 674412 VREF Power Supply Rejection VCC Power Supply Rejection 674404 674413 Test Circuit 674405 5 www.national.com LM9044 Block Diagram 674414 The non-inverting input bias current is scaled to the VREF voltage. As the VREF voltage increases, or decreases, this bias current will change proportionally. Application Information CIRCUIT DESCRIPTION The LM9044 is a single channel device intended to act as a linear interface between a zirconium dioxide oxygen sensor and an A-to-D convertor. The LM9044 is fabricated in Bipolar technology and requires two supplies: a nominal 12V automotive supply (i.e. VBATTERY), and a well regulated 5V supply. The IC consists of a single channel differential input amplifier with a nominal DC gain of 4.5 V/V. The differential inputs have a guaranteed common mode voltage operating range of 1V above and below ground. The circuitry also contains provisions for default output voltage in the cases of cold sensor and open sensor wiring. Additional support circuitry includes one pin for an optional user programmed low pass filter. OPEN INPUT PINS DEFAULTS In any remote sensor application it is desirable to be able to deal with the possibility of open connections between the sensor and the control module. The LM9044 is capable of providing a default output voltage should either, or both, of the wires to the Lambda sensor open. The two inputs handle the open circuit condition differently. For the case of an open connection at the non-inverting input, the device would react exactly the same as for the Cold Sensor condition. The internal non-inverting input bias current (380 nA typical) flowing through the differential input resistance (1.2 M typical) would cause the typical output voltage to be at a value defined by: COLD SENSOR Typically, a Lambda sensor will have an impedance of less than 10 k when operating at temperatures between 300C, and 500C. When a Lambda sensor is not at operating temperature, its impedance can be more than 10 Meg. Any voltage signal that may be developed is seriously attenuated. During this high impedance condition the LM9044 will provide a default output voltage. While the Lambda sensor is high impedance the internal noninverting input bias current (380 nA typical) will flow through the differential input resistance (1.2 M typical) and out the inverting input pin to ground. This will cause a voltage to be developed across the differential inputs: VOUT = ((380 nA x 1.2M) x 4.50 ) VOUT = 2.0V The inverting input would still be connected to the Lambda sensor ground, so common mode signals would still need to be considered in this condition. For the case of an open connection of the inverting input, the device output stage switches from the amplifier output to a resistive voltage divider. The LM9044 has a comparator to monitor the voltage on the inverting input pin, and a 65 A (typical) current source that will force the pin high if the pin is open. When the voltage on the inverting pin goes above typically 1.5V, the comparator will switch the output pin from the amplifier output to the resistive voltage divider stage. In this case, the default VOUT is not dependent on the gain stage, and any signal on the non-inverting input will be ignored. In this condition VOUT is: VIN(DIFF) = 380 nA x 1.2 M VIN(DIFF) = 456 mV The 456 mV across differential input resistance will be the dominant input signal, and the typical VOUT will be: VOUT = VREF x ((14k + 4k) / (26.5k + 14k + 4k)) VOUT = VIN(DIFF) x 4.50 VOUT = VREF x 0.4045 VOUT = 456 mV x 4.50 When VREF is at 5.0V, VOUT is defined as: VOUT = 2.0V VOUT = 5.0V x 0.4045 As the Lambda sensor is heated, and the sensor impedance begins to drop, the voltage signal from the sensor will become the dominate signal. www.national.com VOUT = 2.0V In the cases where both the inverting and non-inverting pins are open, the open inverting pin condition (i.e.: a voltage divider across the output) will be the dominant condition. 6 current. The VCC pin should be bypassed with a minimum 0.01 F capacitor to the Ground pin, and should be located as close to the device as possible. Some applications may require an additional bypass capacitance if the system voltage is unusually noisy. OUTPUT RESISTANCE Under normal operating conditions the output pin resistance is typically 200. If the LM9044 is operating in a default output mode due an open connection on the inverting input, the output resistance will typically appear to be close to 11 k. An external output filter capacitor value of no more than 0.01 F is generally recommended. Since the output pin voltage drive is basically a simple NPN emitter follower, the output pin pull-down is done by the internal feedback resistor string. With larger value capacitors on the output pin the effect will be somewhat similar to a voltage peak detector where the output capacitor is charged through the 200 resistor, and discharged back through the 200 resistor and the 18 k feedback resistor string to ground. The output resistance provides current limiting for the output stage should it become shorted to Ground. Any DC loading of the output will cause an error in the output voltage. SETTING THE BANDWIDTH The LM9044 bandwidth is limited by an external capacitor (CF) on the RF pin. This pin has an internal 175 k resistor. The external capacitor and the internal resistor form a simple RC low-pass filter with a corner frequency (fC) defined as: fC = 1/ (2 x x 175 k x CF) With a CF capacitor value of 0.001 F, the corner frequency is: fC = 1/ (2 x x 175 k x 0.001 F) fC = 909 Hz INPUT FILTERING Filtering at the differential inputs is strongly recommended. Both the differential voltage signal and the common mode voltage signal should have low pass filters. Input filtering is accomplished with series resistors on the input pins, and appropriate bypass capacitors. Typical input pin series resistance values are in the 100 to 1k range. Series resistance values larger than 1k will generate offset voltages that affect the accuracy of the signal voltage seen at the differential input pins. SUPPLY BYPASSING For best performance the LM9044 requires a VREF supply which is stable and noise free. The same 5V reference supply used for the A/D converter is the recommended LM9044 VREF supply. The LM9044 VCC pin has an internal zener shunt voltage regulator, typically 7.5V, and requires a series resistor to limit the Simplified Internal Schematic 674401 7 www.national.com LM9044 Any common mode voltage transient on the inverting input pin which goes above the comparator threshold will immediately cause the output to switch to the resistive voltage divider mode. The output will return to normal operation when the voltage on the inverting input falls below the 1.5V threshold. LM9044 Physical Dimensions inches (millimeters) unless otherwise noted Plastic Chip Carrier Package Order Number LM9044V NS Package Number V20A www.national.com 8 LM9044 Notes 9 www.national.com LM9044 Lambda Sensor Interface Amplifier Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Design Support Amplifiers www.national.com/amplifiers WEBENCH(R) Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage Reference www.national.com/vref Design Made Easy www.national.com/easy PowerWise(R) Solutions www.national.com/powerwise Solutions www.national.com/solutions Serial Digital Interface (SDI) www.national.com/sdi Mil/Aero www.national.com/milaero Temperature Sensors www.national.com/tempsensors SolarMagicTM www.national.com/solarmagic Wireless (PLL/VCO) www.national.com/wireless Analog University(R) www.national.com/AU THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. 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