LMP8270 DS201307 LMP8270MA LMP8270MAX 10VOS1 CSP-9-111C2 CSP-9-111S2

High Common Mode, Gain of 20, Precision Voltage Difference Amplifier General Description Features The LMP8270 is a fixed gain

LMP8270 LMP8270 High Common Mode, Gain of 20, Precision Voltage Difference Amplifier General Description Features The LMP8270 LMP8270 is a fixed gain differential amplifier with a -2V to 27V input common mode voltage range and a supply voltage range of 4.75V to 5.5V. The LMP8270 LMP8270 is part of the LMPTM precision amplifier family which will detect, amplify and filter small differential signals in the presence of high common mode voltages. The gain is fixed at 20 and is adequate to drive an ADC to full scale in most cases. This gain is achieved in two stages, a preamplifier with a fixed gain of 10 and a second stage amplifier with a fixed gain of 2. The internal signal path between these two stages is brought out on two pins, A1 and A2, which provide a connection for a filter network. The LMP8270 LMP8270 will operate with reduced specifications over the extended common mode input voltage range of -2V to 36V. This feature makes the device suitable for applications with load dump in automotive systems. Typical Values, TA = 25°C ± 1 mV max n Input offset voltage ± 15 µV/°C max n TCVOS n CMRR 80 dB min n Extended CMVR -2V to 36V n Output voltage swing Rail-to-rail n Bandwidth 80 kHz n Operating temperature range (ambient) -40°C to 125°C n Supply voltage 4.75V to 5.5V n Supply current 1 mA Applications n Fuel injection control n High and low side driver configuration current sensing n Power management systems Typical Application Low Side Current Sensing 20130702 LMPTM is a trademark of National Semiconductor Corporation. © 2005 National Semiconductor Corporation DS201307 DS201307 www.national.com LMP8270 LMP8270 High Common Mode, Gain of 20, Precision Voltage Difference Amplifier December 2005 LMP8270 LMP8270 Absolute Maximum Ratings (Note 1) Junction Temperature (Note 3) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Soldering Information +150°C Infrared or Convection (20 sec) 235°C Wave Soldering Lead Temp. (10 sec) 260°C ESD Tolerance (Note 2) Human Body Model Operating Ratings (Note 1) ± 4000V ± 2000V For +IN and -IN For all other pins Temperature Range 200V Supply Voltage (VS - GND) Packaged Device (Note 3) 5.75V Machine Model Supply Voltage (VS - GND) Voltage on +IN and -IN -7V to 45V Storage Temperature Range 4.75V to 5.5V Package Thermal Resistance (JA (Note 3) -5V to 42V Transient (400 ms) -40°C to +125°C 8-Pin SOIC 190°C/W -65°C to +150°C 5V Electrical Characteristics (Note 4) Unless otherwise specified, all limits are guaranteed for TA = 25°C, VS = 5V, GND = 0V, -2V VCM 27V, RL = Open. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions VOS Input Offset Voltage Input Offset Voltage Drift VCM = VS/2 25°C TA 125°C -40°C TA 25°C A2 IB Input Bias Current of A2 (Note 7) Typ (Note 5) Max Units ± 0.25 ±6 ±6 VCM = VS/2 (Note 6) TCVOS Min ± 1.0 ± 15 ± 20 mV -20 µV/°C pA ± 20 IS 1.0 Supply Current nA 1.2 1.4 mA RCM Input Impedance Common Mode 160 200 240 k RDM Input Impedance Differential Mode 320 400 480 k CMVR Input Common-Mode Voltage Range -2 +27 V ECMVR Extended Common-Mode Voltage Range -2 36 V DC CMRR DC Common Mode Rejection Ratio 0°C TA 125°C -2V VCM 27V -2V VCM 36V 80 60 -40°C TA 0°C -2V VCM 27V -2V VCM 36V 77 60 f = 1 kHz 80 AC CMRR AC Common Mode Rejection Ratio -2V VCM 27V (Note 8) PSRR Power Supply Rejection Ratio RF-INT Filter Resistor f = 10 kHz 4.75V VS 5.5V dB 95 dB 78 70 80 97 100 dB 103 ± 20 TCRF-INT Filter Resistor Drift AV 103 Total Gain 19.8 k ppm/°C 20.2 V/V ±2 Gain Drift 20 ± 25 ppm/°C AV1 A1 Gain 9.9 10 10.1 V/V AV2 A2 Gain 1.98 2 2.02 V/V A1 VOUT A1 Output Voltage Swing 0.004 0.01 VOL VOH A2 VOUT A2 Output Voltage Swing (Notes 9, 10) 4.80 RL = 100 k on Output VOL VOH RL = 10 k on Output 4.95 0.007 4.80 4.99 Slew Rate (Note 11) www.national.com 0.03 VOH SR VOL 4.95 0.7 2 0.02 V V V V/µs (Note 4) (Continued) Unless otherwise specified, all limits are guaranteed for TA = 25°C, VS = 5V, GND = 0V, -2V VCM 27V, RL = Open. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min Typ (Note 5) Max Units BW Bandwidth 80 kHz Noise 0.1 Hz to 10 Hz 5.7 µVPP Spectral Density f = 1 kHz 452 nV/ Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics Tables. Note 2: Human Body Model is 1.5 k in series with 100 pF. Machine Model is 0 in series with 200 pF. Note 3: The maximum power dissipation is a function of TJ(MAX), JA, and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ(MAX) - TA)/ JA . All numbers apply for packages soldered directly onto a PC board. Note 4: Electrical table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very limited self-heating of the device. Note 5: Typical values represent the parametric norm at the time of characterization. Note 6: The VOS maximum limit indicated does not include effects of lifetime drift, see Application Note. Note 7: Positive current corresponds to current flowing into the device. Note 8: AC Common Mode Signal is a 24 VPP sine-wave (0V to 24V) at the given frequency. Note 9: For VOL, RL is connected to VS and for VOH, RL is connected to GND. Note 10: For this test input is driven from A1 stage. Note 11: Slew rate is the average of the rising and falling slew rates. Connection Diagram 8-Pin SOIC 20130703 Top View Ordering Information Package 8-Pin SOIC Part Number LMP8270MA LMP8270MA LMP8270MAX LMP8270MAX Package Marking Transport Media 95 Units/Rail LMP8270MA LMP8270MA 2.5k Units Tape and Reel 3 NSC Drawing M08A www.national.com LMP8270 LMP8270 5V Electrical Characteristics LMP8270 LMP8270 Typical Performance Characteristics Unless otherwise specified: TA = 25°C, VS = 5V, VCM = VS/2 VOS vs. VCM Over Temperature Typical VOS vs. Temperature 20130721 20130715 Input Bias Current Over Temperature (A1 Inputs) Input Bias Current Over Temperature (A2 Input) 20130718 20130728 Input Bias Current Over Temperature (A2 Input) Input Referred Voltage Noise vs. Frequency 20130706 20130720 www.national.com 4 (Continued) PSRR vs. Frequency VOS vs. Supply Voltage 20130723 20130722 Gain vs. Frequency Over Temperature Gain vs. Frequency Over Temperature 20130712 20130711 Offset Voltage Distribution Filter Resistor 20130717 20130716 5 www.national.com LMP8270 LMP8270 Typical Performance Characteristics Unless otherwise specified: TA = 25°C, VS = 5V, VCM = VS/2 LMP8270 LMP8270 Typical Performance Characteristics Unless otherwise specified: TA = 25°C, VS = 5V, VCM = VS/2 (Continued) CMRR vs. Frequency Step Response 20130708 20130714 Settling Time (Rising Edge) Settling Time (Falling Edge) 20130710 20130709 Output Voltage Swing vs. RL to VS Output Voltage Swing vs. RL to GND 20130713 www.national.com 20130707 6 LMP8270 LMP8270 The LMP8270 LMP8270 is a single supply amplifier with a fixed gain of 20 and an extended common mode voltage range of -2V to 36V. The fixed gain is achieved in two separate stages, a preamplifier with gain of +10 and a second stage amplifier with gain of +2. A block diagram of the LMP8270 LMP8270 is shown in Figure 1. The long term reliability tests include Operating Life Time, OPL, performed at 150°C for an extended period of time; Temperature Humidity Bias Testing, THBT, at 85°C and 85% humidity for an extended period of time and repeated cycles of TMCL. The Offset Voltage was measured again after each reliability test at room temperature. The Offset Voltage Drift is the difference between the initial measurement, before preconditioning, and the later measurement, post preconditioning and reliability test. Figure 2 below shows the offset voltage drift after preconditioning and 1000 hours of OPL. 20130701 FIGURE 1. The overall offset of the LMP8270 LMP8270 is minimized by trimming amplifier A1. This is done in such a way that the output referred offset of A1 cancels the input referred offset of A2 or 10VOS1 10VOS1 = -VOS2. Because of this offset voltage relationship, the offset of each individual amplifier stage may be more than the limit specified for the overall system in the datasheet tables. If the signal going from A1 to A2 is amplified or attenuated (by use of amplifiers and resistors), the overall LMP8270 LMP8270 offset will be affected as a result. Filtering the signal between A1 and A2 or simply connecting the two pins will not change the offset of the LMP8270 LMP8270. Referencing the input referred offset voltages of each input stage, the following relationship holds: 20130727 FIGURE 2. Figure 3 shows the offset voltage drift after preconditioning and 1000 hours of THBT. If the signal on pin 3 is scaled, attenuated or amplified, by a factor X, then the offset of the overall system will become: LIFETIME DRIFT Input Offset Voltage is an electrical parameter which may drift over time. This drift, known as lifetime drift, is very common in operational amplifiers; however, its effect is more evident in precision amplifiers. This is due to the very low Input Offset Voltage specifications in these amplifiers. Numerous reliability tests have been performed to characterize this drift for the LMP8270 LMP8270. Prior to each long term reliability test the Input Offset Voltage of the LMP8270 LMP8270 was measured at room temperature. The LMP8270 LMP8270 was then subjected to a preconditioning sequence consisting of a 16 20130726 FIGURE 3. 7 www.national.com LMP8270 LMP8270 hour bake at 125°C; an unbiased 168 hour Temperature Humidity Storage Test, THST, at 85°C and 85% humidity; four passes of infra-red reflow with a maximum temperature of 260°C; and finally one hundred 30 min Temperature Cycles, TMCL, between -65°C and 150°C (15 min at each temperature). Application Note LMP8270 LMP8270 Application Note (Continued) POWER SUPPLY DECOUPLING Figure 4 shows the offset voltage drift after preconditioning and a total of 1000 TMCL cycles. In order to decouple the LMP8270 LMP8270 from AC noise on the power supply, it is recommended to use a 0.1 µF on the supply pin. It is best to use a 0.1 µF capacitor in parallel with a 10 µF capacitor. This will generate an AC path to ground for most frequency ranges and will greatly reduce the noise introduced by the power supply. CURRENT LOOP RECEIVER Many types of process control instrumentation use 4 to 20 mA transmitters to transmit the sensor's analog value to a central control room. The LMP8270 LMP8270 can be used as a current loop receiver as shown in Figure 5. 20130725 FIGURE 4. 20130724 FIGURE 5. it to sense signals outside of its supply voltage range. Also, the LMP8270 LMP8270 has very high CMRR, which enables it to sense very small signals in the presence of larger common mode signals. The system in Figure 6 couples these two characteristics of the LMP8270 LMP8270 in an automotive application. The signal through RS1 is detected and amplified by the LMP8270 LMP8270 in the presence of a common mode signal of up to 27V with the highest accuracy. HIGH SIDE CURRENT SENSING High side current measurement requires a differential amplifier with gain. Here the DC voltage source represents a common mode voltage with the +IN input at the supply voltage and the -IN input very close to the supply voltage. The LMP8270 LMP8270 can be used with a common mode voltage, VDC in this case, of up to 36V. The LMP8270 LMP8270 can be used for high side current sensing. The large common mode voltage range of this device allows www.national.com 8 LMP8270 LMP8270 Application Note (Continued) 20130729 FIGURE 6. LOW SIDE CURRENT SENSING Low side current measurements can cause a problem for operational amplifiers by exceeding the negative common mode voltage limit of the device. In Figure 7, the load current is returning to the power source through a common connection that has a parasitic resistance. The voltage drop across the parasitic resistances can cause the ground connection of the measurement circuits to be at a positive voltage with respect to the common side of the sense resistor. This will result in one or both of the inputs being negative with respect to the circuit's ground. The LMP8270 LMP8270 has a wide input common mode voltage range of -2V to 36V and will function in this condition. 20130730 FIGURE 7. 9 www.national.com LMP8270 LMP8270 Application Note (Continued) SECOND ORDER LOW-PASS FILTER The LMP8270 LMP8270 can be used to build a second order SallenKey low pass filter. The general filter is shown in Figure 8: 20130753 20130731 FIGURE 9. FIGURE 8. Using Equation (1) the filter parameters can be calculated as follows: With the general transfer function: (1) Where: and for the LMP8270 LMP8270, R1 = 100 k. Setting R1 = R2 and C1 = C2 results in a low-pass filter with Q = 1. Since the values of resistors are predetermined, the corner frequency of this implementation of the filter depends on the capacitor values. K represents the sum of DC closed loop gain and the nonideality behavior of the operational amplifier. Assuming ideal behavior, the equation for K simply reduces to the DC gain, which is +2 for the LMP8270 LMP8270. The LMP8270 LMP8270 can be used to realize this configuration as shown in figure Figure 9: www.national.com GAINS OTHER THAN 20 The LMP8270 LMP8270 has an internal gain of +20; however, this gain can be modified. The signal path between the two amplifiers is available as external pins. 10 LMP8270 LMP8270 Application Note (Continued) GAINS LESS THAN 20 Figure 10 shows the configuration used to reduce the LMP8270 LMP8270 gain. 20130750 FIGURE 11. The total gain is given by: 20130747 FIGURE 10. Where: which can be rearranged to calculate RG: and The inverting gain of the second amplifier is set at 2, giving a total system gain of 20. The non-inverting gain which is achieved through positive feedback can be less than or equal to this gain without any issues. This implies a total system gain of 40 or less is easily achievable. Once the positive gain surpasses the negative gain, the system might oscillate. GAINS GREATER THAN 20 A higher gain can be achieved by using positive feedback on the second stage amplifier, A2, of LMP8270 LMP8270. Figure 11 shows the configuration: 11 www.national.com LMP8270 LMP8270 High Common Mode, Gain of 20, Precision Voltage Difference Amplifier Physical Dimensions inches (millimeters) unless otherwise noted 8-Pin SOIC NS Package Number M08A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. BANNED SUBSTANCE COMPLIANCE National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2 CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2 CSP-9-111S2) and contain no ``Banned Substances'' as defined in CSP-9-111S2 CSP-9-111S2. Leadfree products are RoHS compliant. National Semiconductor Americas Customer Support Center Email: new.feedback@nsc.com Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Support Center Email: ap.support@nsc.com National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: jpn.feedback@nsc.com Tel: 81-3-5639-7560