LMP8271

LMP8271,LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifiers PRELIMINARY January 2005 LMP8271, LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifiers General Description The LMP™8271, LMP8276 are fixed gain differential amplifiers with a -2V to 27V input common mode voltage range and a supply voltage range of 4.5V to 5.5V. The LMP8271, LMP8276 are precision amplifiers 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 fixed gain is achieved in two separate stages, a pre-amplifier with gain of +10 and a second stage amplifier with a gain of +2. The internal signal path is brought out on two pins that provide a connection for a filter network. The LMP8271, LMP8276 will function with reduced specifications over the extended common mode input voltage range of -5 to 36 Volts. This feature makes the device suitable for applications with load dump in automotive systems. The midrail offset adjustment pin enables the user to utilize this device for bidirectional current sensing. This is achieved by adjusting an externally set voltage reference. Accurate bidirectional load current measurements are achieved when monitoring the output with respect to this reference voltage Features n n n n n n n n n n n n n Bidirectional Current Sense Capability Typical Values, TA = 25˚C Input Offset Voltage 1mV max TCVos (LMP8271) 15µV/˚C max TCVos (LMP8276) 30µV/˚C max CMRR 80dB Min Extended CMVR -5V to 36V Output Voltage Swing Rail to Rail Bandwidth 80KHz Operating Temperature Range (Ambient) -40˚C to 125˚C Operating Temperature Range (bare die) -40˚C to 150˚C Supply Voltage 4.5V to 5.5V Supply Current 1mA Applications n Fuel Injection Control n Low Side Driver Configuration Current Sensing n Power Management Systems Typical Application Typical Application: Low side Current Sensing 20130801 LMP™ is a trademark of National Semiconductor Corporation. © 2005 National Semiconductor Corporation DS201308 www.national.com LMP8271, LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifier Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. ESD Tolerance (Note 2) Human Body Model For input pins only For All other pins Machine Model Supply Voltage (VS - GND) Junction Temperature (Note 3) Soldering Information Infrared or Convection (20 sec) Wave Soldering Lead Temp. (10 sec) +150˚C max 235˚C 260˚C ± 4000V ± 2000V 200V 5.75V Operating Ratings (Note 1) Temperature Range (Note 3) Packaged devices(Note 3) Bare Die Junction Temperature(Note 3) -40˚C to +125˚C -40˚C to +150˚C 4.5V to 5.5V 190˚C/W CMVR Continuous Transient (300 ms) Storage Temperature Range -5 to 42 Volts -TBD to 45 Volts -65˚C to +150˚C (Note 7) Supply Voltage (VS –GND) Package Thermal Resistance (θJA (Note 3)) 8–Pin SOIC 5V Electrical Characteristics Symbol Parameter Unless otherwise specified, all limits guaranteed for TA = 25˚C, VS = 5V, GND= 0, -2V≤VCM ≤27V. Boldface limits apply at the temperature extremes. Conditions Min Typ (Note 4) Max Units VOS TC VOS TC VOS A2 IB IS RCM RDM CMVR ECMVR DC CMRR AC CMRR PSRR RF-INT TCRF-INT Input Offset Voltage Input Offset Voltage Drift Input Offset Voltage Drift Input Bias Current of A2 Supply Current Input impedance Common Mode Input impedance Differential Mode Input Common-Mode Voltage Range Extended Common-Mode Voltage Range DC Common Mode Rejection Ratio AC Common Mode Rejection Ratio Power Supply Rejection Ratio Filter Resistor Filter Resistor Drift Midscale Offset Scaling Accuracy (Pin 7) VCM = Vs/2 LMP8271 LMP8276 (Note 5) 0.6 TBD 160 320 Continuous -2 -5 -2V≤VCM≤ 27V -5V≤VCM≤ 36V -2V≤VCM≤ 27V -2V≤VCM≤ 27V 4.5V≤VS≤ 5.5V f = 1KHz f = 10KHz 80 80 TBD TBD TBD TBD 97 ± 0.25 ±6 ±6 1.0 200 400 1.0 mV µV/˚C µV/˚C µA mA KΩ KΩ V V dB dB dB ± 15 ± 30 ± 20 1.2 TBD 240 480 +27 36 100 TBD 103 1 KΩ ppm/˚C % V/V AV Total Gain Gain Error Gain Drift 20 ±1 ± 25 RL= 100KΩ on Output RL= 100KΩ on Output VOL VOH 4.80 0.01 4.80 VOL VOH 0.01 % ppm/˚C Volts Volts A1 VOUT A2 VOUT A1 Output Voltage Swing A2 Output Voltage Swing www.national.com 2 LMP8271, LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifier 5V Electrical Characteristics Symbol Parameter (Note 7) (Continued) Unless otherwise specified, all limits guaranteed for TA = 25˚C, VS = 5V, GND= 0, -2V≤VCM ≤27V. Boldface limits apply at the temperature extremes. Conditions Min Typ (Note 4) 0.7 80 TBD TBD Max Units SR BW Noise Slew Rate (Note 6) Bandwidth 0.1Hz ro 10Hz Spectral Density V/µs KHz µVpp nV/√Hz 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, 1.5 kΩ in series with 100 pF. Machine model: 0Ω in series with 200 pF. Note 3: The maximum power dissipation is a function of TJ(MAX), θJA, and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ(MAX) - TA)/ θJA . All numbers apply for packages soldered directly onto a PC board. Note 4: Typical values represent the most likely parametric norm. Note 5: Positive current corresponds to current flowing into the device. Note 6: Slew rate is the average of the rising and falling slew rates. Note 7: 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. Connection Diagram 8–Pin SOIC 20130802 Top View Application Note The LMP8271, LMP8276 are 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 pre-amplifier with gain of +10 and a second stage amplifier with gain of +2. A block diagram of the LMP8271, LMP8276 is shown in Figure 1. The overall offset of the LMP8271, LMP8276 is minimized by trimming amplifier A1. This is done so that the output referred offset of A1 cancels the input referred offset of A2 or 10VOS1 = -VOS2 Because of this offset voltage relationship, the offset of each individual amplifier stage maybe more than the limit specified for the overall system in the datasheet tables. Care must be given when pin 3 and 4, A1 and A2, are connected to each other. If the signal going from A1 to A2 is amplified or attenuated (by use of amplifiers and resistors), the overall LMP8271, LMP8276 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 LMP8271, LMP8276. Referencing input referred offset voltages, the following relationship holds: 20130803 FIGURE 1. If the signal on pin 3 is scaled, attenuated or amplified, by a factor X then the offset of the overall system will become: 3 www.national.com LMP8271, LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifier Application Note (Continued) Note that the offset pin, pin 7, needs to be connected at all times. If the pin is left floating, the LMP8271 and LMP8276 will be operating in an undefined mode. Also pin 7 should be driven from a low impedance source. This represents a value that the LMP8271 and LMP8276 have not been optimized and trimmed for and may very well be above the limits indicated in the electrical characteristics tables. Midrail Offset Adjustment Pin The external midrail offset adjustment pin enables the user to utilize this device for bidirectional current sensing. If the offset pin, pin 7, is connected to ground then the LMP8271, LMP8276 are capable of sensing positive signals. When the offset pin is connected to VS then 1/2VS is added to the output and under this condition the amplifier can sense both positive and negative signals. If this offset pin is connected to any voltage between ground and VS, then the output is increased by a voltage equal to half of that offset, e.g. If the offset is connected to VX, then the output increases by 1/2VX. The following figure shows how this works: 20130806 FIGURE 2. www.national.com 4 LMP8271,LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifiers Notes 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. BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. 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 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.