January 2005 LMP8271, LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifiers General Description Features The LMP™8271, LMP8276 are fixed gain differential ampli- n n n n n n n n n n n n n fiers 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 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 Amplifiers PRELIMINARY LMP8271, LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifier 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 ESD Tolerance (Note 2) +150˚C max Infrared or Convection (20 sec) 235˚C Wave Soldering Lead Temp. (10 sec) 260˚C Human Body Model ± 4000V ± 2000V For input pins only For All other pins Machine Model Operating Ratings (Note 1) Temperature Range (Note 3) 200V Supply Voltage (VS - GND) CMVR Continuous Transient (300 ms) Storage Temperature Range 5.75V -40˚C to +125˚C Bare Die Junction Temperature(Note 3) -40˚C to +150˚C Supply Voltage (VS –GND) -5 to 42 Volts 4.5V to 5.5V Package Thermal Resistance (θJA (Note 3)) -TBD to 45 Volts 8–Pin SOIC -65˚C to +150˚C 5V Electrical Characteristics Packaged devices(Note 3) 190˚C/W (Note 7) Unless otherwise specified, all limits guaranteed for TA = 25˚C, VS = 5V, GND= 0, -2V≤VCM ≤27V. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min Typ (Note 4) ± 0.25 ±6 ±6 VOS Input Offset Voltage VCM = Vs/2 TC VOS Input Offset Voltage Drift LMP8271 TC VOS Input Offset Voltage Drift LMP8276 A2 IB Input Bias Current of A2 (Note 5) IS Supply Current 0.6 TBD RCM Input impedance Common Mode RDM Input impedance Differential Mode CMVR Input Common-Mode Voltage Range ECMVR Extended Common-Mode Voltage Range DC CMRR DC Common Mode Rejection Ratio -2V≤VCM≤ 27V -5V≤VCM≤ 36V AC CMRR AC Common Mode Rejection Ratio -2V≤VCM≤ 27V -2V≤VCM≤ 27V PSRR Power Supply Rejection Ratio 4.5V≤VS≤ 5.5V RF-INT Filter Resistor TCRF-INT Filter Resistor Drift Continuous 1.0 mV µV/˚C 1.0 1.2 TBD mA 160 200 240 KΩ 320 400 480 KΩ -2 +27 V -5 36 V µA dB f = 1KHz TBD dB f = 10KHz TBD TBD TBD 97 dB 100 103 TBD 20 Gain Error Gain Drift A1 VOUT A1 Output Voltage Swing RL= 100KΩ on Output VOL A2 VOUT A2 Output Voltage Swing RL= 100KΩ on Output VOL VOH VOH KΩ ppm/˚C 1 2 µV/˚C 80 80 Total Gain www.national.com Units ± 15 ± 30 ± 20 Midscale Offset Scaling Accuracy (Pin 7) AV Max % V/V ±1 ± 25 ppm/˚C 0.01 Volts 0.01 Volts % 4.80 4.80 (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. Symbol Parameter Conditions Min Typ (Note 4) Max Units SR Slew Rate (Note 6) 0.7 BW Bandwidth 80 V/µs KHz Noise 0.1Hz ro 10Hz TBD µVpp Spectral Density TBD 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 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: 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. 20130803 If the signal on pin 3 is scaled, attenuated or amplified, by a factor X then the offset of the overall system will become: FIGURE 1. 3 www.national.com LMP8271, LMP8276 High Common Mode, Gain of 20, Bidirectional Precision Voltage Difference Amplifier 5V Electrical Characteristics 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 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. 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