LMP2014MT Quad High Precision, Rail-to-Rail Output Operational Amplifier General Description Features TM The LMP2014MT is a member of National’s new LMP precision amplifier family. The LMP2014MT offers unprecedented accuracy and stability while also being offered at an affordable price. This device utilizes patented techniques to measure and continually correct the input offset error voltage. The result is an amplifier which is ultra stable over time and temperature. It has excellent CMRR and PSRR ratings, and does not exhibit the familiar 1/f voltage and current noise increase that plagues traditional amplifiers. The combination of the LMP2014 characteristics makes it a good choice for transducer amplifiers, high gain configurations, ADC buffer amplifiers, DAC I-V conversion, and any other 2.7V-5V application requiring precision and long term stability. Other useful benefits of the LMP2014 are rail-to-rail output, a low supply current of 3.7 mA, and wide gain-bandwidth product of 3 MHz. These extremely versatile features found in the LMP2014 provide high performance and ease of use. (For VS = 5V, Typical unless otherwise noted) n Low guaranteed VOS over temperature n Low noise with no 1/f n High CMRR n High PSRR n High AVOL n Wide gain-bandwidth product n High slew rate n Low supply current n Rail-to-rail output n No external capacitors required 60 µV 35nV/ 130 dB 120 dB 130 dB 3 MHz 4 V/µs 3.7 mA 30 mV Applications n Precision instrumentation amplifiers n Thermocouple amplifiers n Strain gauge bridge amplifier Connection Diagram 14-Pin TSSOP 20132939 Top View Ordering Information Package Part Number 14-Pin TSSOP LMP2014MT LMP2014MTX © 2005 National Semiconductor Corporation Temperature Range Package Marking 0˚C to 70˚C LMP2014MT DS201329 Transport Media 94 Units/Rail 2.5k Units Tape and Reel NSC Drawing MTC14 www.national.com LMP2014MT Quad High Precision, Rail-to-Rail Output Operational Amplifier July 2005 LMP2014MT Absolute Maximum Ratings (Note 1) Differential Input Voltage If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Current at Input Pin ± Supply Voltage 30 mA Current at Output Pin 30 mA Current at Power Supply Pin 50 mA ESD Tolerance Human Body Model 2000V Machine Model Operating Ratings (Note 1) 200V Supply Voltage Supply Voltage 5.8V 2.7V to 5.25V Storage Temperature Range Common-Mode Input Voltage −65˚C to 150˚C Operating Temperature Range −0.3 ≤ VCM ≤ VCC +0.3V LMP2014MT, LMP2014MTX Lead Temperature (soldering 10 sec.) 0˚C to 70˚C +300˚C 2.7V DC Electrical Characteristics V+ = 2.7V, V- = 0V, V TCVOS Unless otherwise specified, all limits guaranteed for T J = 25˚C, = 1.35V, VO = 1.35V and RL > 1 MΩ. Boldface limits apply at the temperature extremes. Typ (Note 2) Max (Note 3) Input Offset Voltage 0.8 30 60 µV Offset Calibration Time 0.5 10 12 ms Symbol VOS CM Parameter Conditions Min (Note 3) Units Input Offset Voltage 0.015 µV/˚C Long-Term Offset Drift 0.006 µV/month Lifetime VOS Drift 2.5 µV IIN Input Current -3 pA IOS Input Offset Current 6 pA RIND Input Differential Resistance 9 MΩ CMRR Common Mode Rejection Ratio 95 90 130 dB PSRR Power Supply Rejection Ratio 95 90 120 dB AVOL Open Loop Voltage Gain RL = 10 kΩ 95 90 130 RL = 2 kΩ 90 85 124 2.63 2.655 2.68 VO Output Swing −0.3 ≤ VCM ≤ 0.9V 0 ≤ VCM ≤ 0.9V RL = 10 kΩ to 1.35V VIN(diff) = ± 0.5V 0.033 RL = 2 kΩ to 1.35V VIN(diff) = ± 0.5V 2.615 2.615 IS Output Current Sourcing, VO = 0V VIN(diff) = ± 0.5V 5 3 12 Sinking, VO = 5V VIN(diff) = ± 0.5V 5 3 18 Supply Current per Channel www.national.com 0.919 2 0.070 0.075 V 2.65 0.061 IO dB 0.085 0.105 V mA 1.20 1.50 mA TJ = 25˚C, V+ = 2.7V, V - = 0V, VCM = 1.35V, VO = 1.35V, and RL > 1 MΩ. Boldface limits apply at the temperature extremes. Symbol Parameter GBW Gain-Bandwidth Product SR θm Conditions Min (Note 3) Typ (Note 2) Max (Note 3) Units 3 MHz Slew Rate 4 V/µs Phase Margin 60 Deg Gm Gain Margin −14 en Input-Referred Voltage Noise 35 in Input-Referred Current Noise enp-p Input-Referred Voltage Noise trec Input Overload Recovery Time pA/ RS = 100Ω, DC to 10 Hz 850 nVpp 50 ms 5V DC Electrical Characteristics - 5V, V = 0V, V Symbol VOS CM dB nV/ Unless otherwise specified, all limits guaranteed for T = 2.5V, VO = 2.5V and RL > 1MΩ. Boldface limits apply at the temperature extremes. = 25˚C, V+ = Typ (Note 2) Max (Note 3) Input Offset Voltage 0.12 30 60 µV Offset Calibration Time 0.5 10 12 ms Parameter Conditions Min (Note 3) J Units Input Offset Voltage 0.015 µV/˚C Long-Term Offset Drift 0.006 µV/month Lifetime VOS Drift 2.5 µV IIN Input Current -3 pA IOS Input Offset Current 6 pA TCVOS RIND Input Differential Resistance CMRR Common Mode Rejection Ratio PSRR Power Supply Rejection Ratio AVOL Open Loop Voltage Gain VO Output Swing 9 MΩ 100 90 130 dB 95 90 120 dB RL = 10 kΩ 105 100 130 RL = 2 kΩ 95 90 132 4.92 4.95 4.978 −0.3 ≤ VCM ≤ 3.2 0 ≤ VCM ≤ 3.2 RL = 10 kΩ to 2.5V VIN(diff) = ± 0.5V 0.040 4.875 4.875 RL = 2 kΩ to 2.5V VIN(diff) = ± 0.5V IS Output Current Sourcing, VO = 0V VIN(diff) = ± 0.5V 8 6 15 Sinking, VO = 5V V IN(diff) = ± 0.5V 8 6 17 Supply Current per Channel 0.930 3 0.080 0.085 V 4.919 0.091 IO dB 0.125 0.140 V mA 1.20 1.50 mA www.national.com LMP2014MT 2.7V AC Electrical Characteristics LMP2014MT 5V AC Electrical Characteristics TJ = 25˚C, V+ = 5V, V - = 0V, VCM = 2.5V, VO = 2.5V, and RL > 1MΩ. Boldface limits apply at the temperature extremes. Symbol Parameter GBW Gain-Bandwidth Product SR θm Conditions Min (Note 3) Typ (Note 2) Max (Note 3) Units 3 MHz Slew Rate 4 V/µs Phase Margin 60 deg Gm Gain Margin −15 en Input-Referred Voltage Noise 35 in Input-Referred Current Noise enp-p Input-Referred Voltage Noise trec Input Overload Recovery Time dB nV/ pA/ RS = 100Ω, DC to 10 Hz 850 nVPP 50 ms Note 1: Absolute Maximum Ratings indicate limits beyond which damage 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 test conditions, see the Electrical Characteristics. Note 2: Typical values represent the most likely parametric norm. Note 3: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlations using statistical quality control (SQC) method. www.national.com 4 LMP2014MT Typical Performance Characteristics TA=25C, VS= 5V unless otherwise specified. Supply Current vs. Supply Voltage Offset Voltage vs. Supply Voltage 20132943 20132944 Offset Voltage vs. Common Mode Offset Voltage vs. Common Mode 20132945 20132946 Voltage Noise vs. Frequency Input Bias Current vs. Common Mode 20132903 20132904 5 www.national.com LMP2014MT Typical Performance Characteristics (Continued) PSRR vs. Frequency PSRR vs. Frequency 20132907 20132906 Output Sourcing @ 2.7V Output Sourcing @ 5V 20132947 20132948 Output Sinking @ 2.7V Output Sinking @ 5V 20132949 www.national.com 20132950 6 LMP2014MT Typical Performance Characteristics (Continued) Max Output Swing vs. Supply Voltage Max Output Swing vs. Supply Voltage 20132951 20132952 Min Output Swing vs. Supply Voltage Min Output Swing vs. Supply Voltage 20132953 20132954 CMRR vs. Frequency Open Loop Gain and Phase vs. Supply Voltage 20132908 20132905 7 www.national.com LMP2014MT Typical Performance Characteristics (Continued) Open Loop Gain and Phase vs. RL @ 2.7V Open Loop Gain and Phase vs. RL @ 5V 20132909 20132910 Open Loop Gain and Phase vs. CL @ 2.7V Open Loop Gain and Phase vs. CL @ 5V 20132912 20132911 Open Loop Gain and Phase vs. Temperature @ 2.7V Open Loop Gain and Phase vs. Temperature @ 5V 20132936 www.national.com 20132937 8 LMP2014MT Typical Performance Characteristics (Continued) THD+N vs. AMPL THD+N vs. Frequency 20132913 20132914 0.1 Hz − 10 Hz Noise vs. Time 20132915 9 www.national.com LMP2014MT Application Information THE BENEFITS OF LMP2014 NO 1/f NOISE The wide bandwidth of the LMP2014 enhances performance when it is used as an amplifier to drive loads that inject transients back into the output. ADCs (Analog-to-Digital Converters) and multiplexers are examples of this type of load. To simulate this type of load, a pulse generator producing a 1V peak square wave was connected to the output through a 10 pF capacitor. (Figure 1) The typical time for the output to recover to 1% of the applied pulse is 80 ns. To recover to 0.1% requires 860ns. This rapid recovery is due to the wide bandwidth of the output stage and large total GBW. Using patented methods, the LMP2014 eliminates the 1/f noise present in other amplifiers. That noise, which increases as frequency decreases, is a major source of measurement error in all DC-coupled measurements. Lowfrequency noise appears as a constantly-changing signal in series with any measurement being made. As a result, even when the measurement is made rapidly, this constantlychanging noise signal will corrupt the result. The value of this noise signal can be surprisingly large. For example: If a conventional amplifier has a flat-band noise level of 10nV/ and a noise corner of 10 Hz, the RMS noise at 0.001 . This is equivalent to a 0.50 µV peak-toHz is 1µV/ peak error, in the frequency range 0.001 Hz to 1.0 Hz. In a circuit with a gain of 1000, this produces a 0.50 mV peakto-peak output error. This number of 0.001 Hz might appear unreasonably low, but when a data acquisition system is operating for 17 minutes, it has been on long enough to include this error. In this same time, the LMP2014 will only have a 0.21 mV output error. This is smaller by 2.4 x. Keep in mind that this 1/f error gets even larger at lower frequencies. At the extreme, many people try to reduce this error by integrating or taking several samples of the same signal. This is also doomed to failure because the 1/f nature of this noise means that taking longer samples just moves the measurement into lower frequencies where the noise level is even higher. NO EXTERNAL CAPACITORS REQUIRED The LMP2014 does not need external capacitors. This eliminates the problems caused by capacitor leakage and dielectric absorption, which can cause delays of several seconds from turn-on until the amplifier’s error has settled. MORE BENEFITS The LMP2014 offers the benefits mentioned above and more. It has a rail-to-rail output and consumes only 950 µA of supply current while providing excellent DC and AC electrical performance. In DC performance, the LMP2014 achieves 130 dB of CMRR, 120 dB of PSRR and 130 dB of open loop gain. In AC performance, the LMP2014 provides 3 MHz of gain-bandwidth product and 4 V/µs of slew rate. HOW THE LMP2014 WORKS The LMP2014 uses new, patented techniques to achieve the high DC accuracy traditionally associated with chopperstabilized amplifiers without the major drawbacks produced by chopping. The LMP2014 continuously monitors the input offset and corrects this error. The conventional chopping process produces many mixing products, both sums and differences, between the chopping frequency and the incoming signal frequency. This mixing causes large amounts of distortion, particularly when the signal frequency approaches the chopping frequency. Even without an incoming signal, the chopper harmonics mix with each other to produce even more trash. If this sounds unlikely or difficult to understand, look at the plot (Figure 2), of the output of a typical (MAX432) chopper-stabilized op amp. This is the output when there is no incoming signal, just the amplifier in a gain of -10 with the input grounded. The chopper is operating at about 150 Hz; the rest is mixing products. Add an input signal and the noise gets much worse. Compare this plot with Figure 3 of the LMP2014. This data was taken under the exact same conditions. The auto-zero action is visible at about 30 kHz but note the absence of mixing products at other frequencies. As a result, the LMP2014 has very low distortion of 0.02% and very low mixing products. The LMP2014 eliminates this source of error. The noise level is constant with frequency so that reducing the bandwidth reduces the errors caused by noise. Another source of error that is rarely mentioned is the error voltage caused by the inadvertent thermocouples created when the common "Kovar type" IC package lead materials are soldered to a copper printed circuit board. These steelbased leadframe materials can produce over 35 µV/˚C when soldered onto a copper trace. This can result in thermocouple noise that is equal to the LMP2014 noise when there is a temperature difference of only 0.0014˚C between the lead and the board! For this reason, the lead-frame of the LMP2014 is made of copper. This results in equal and opposite junctions which cancel this effect. OVERLOAD RECOVERY The LMP2014 recovers from input overload much faster than most chopper-stabilized op amps. Recovery from driving the amplifier to 2X the full scale output, only requires about 40 ms. Many chopper-stabilized amplifiers will take from 250 ms to several seconds to recover from this same overload. This is because large capacitors are used to store the unadjusted offset voltage. 20132916 FIGURE 1. www.national.com 10 PRECISION STRAIN-GAUGE AMPLIFIER This Strain-Gauge amplifier (Figure 4) provides high gain (1006 or ~60 dB) with very low offset and drift. Using the resistors’ tolerances as shown, the worst case CMRR will be greater than 108 dB. The CMRR is directly related to the resistor mismatch. The rejection of common-mode error, at the output, is independent of the differential gain, which is set by R3. The CMRR is further improved, if the resistor ratio matching is improved, by specifying tighter-tolerance resistors, or by trimming. (Continued) 20132917 FIGURE 2. 20132918 FIGURE 4. Extending Supply Voltages and Output Swing by Using a Composite Amplifier Configuration: In cases where substantially higher output swing is required with higher supply voltages, arrangements like the ones shown in Figure 5 and Figure 6 could be used. These configurations utilize the excellent DC performance of the LMP2014 while at the same time allow the superior voltage and frequency capabilities of the LM6171 to set the dynamic performance of the overall amplifier. For example, it is possible to achieve ± 12V output swing with 300 MHz of overall GBW (AV = 100) while keeping the worst case output shift due to VOS less than 4 mV. The LMP2014 output voltage is kept at about mid-point of its overall supply voltage, and its input common mode voltage range allows the V- terminal to be grounded in one case (Figure 5, inverting operation) and tied to a small non-critical negative bias in another (Figure 6, non-inverting operation). Higher closed-loop gains are also possible with a corresponding reduction in realizable bandwidth. Table 1 shows some other closed loop gain possibilities along with the measured performance in each case. 20132904 FIGURE 3. INPUT CURRENTS The LMP2014’s input currents are different than standard bipolar or CMOS input currents in that it appears as a current flowing in one input and out the other. Under most operating conditions, these currents are in the picoamp level and will have little or no effect in most circuits. These currents tend to increase slightly when the common-mode voltage is near the minus supply. (See the typical curves.) At high temperatures such as 70˚C, the input currents become larger, 0.5 nA typical, and are both positive except when the VCM is near V−. If operation is expected at low common-mode voltages and high temperature, do not add resistance in series with the inputs to balance the impedances. Doing this can cause an increase in offset voltage. A small resistance such as 1 kΩ can provide some protection against very large transients or overloads, and will not increase the offset significantly. 11 www.national.com LMP2014MT Application Information LMP2014MT Application Information (Continued) 20132920 FIGURE 6. 20132919 It should be kept in mind that in order to minimize the output noise voltage for a given closed-loop gain setting, one could minimize the overall bandwidth. As can be seen from Equation 1 above, the output noise has a square-root relationship to the Bandwidth. In the case of the inverting configuration, it is also possible to increase the input impedance of the overall amplifier, by raising the value of R1, without having to increase the feedback resistor, R2, to impractical values, by utilizing a "Tee" network as feedback. See the LMC6442 data sheet (Application Notes section) for more details on this. FIGURE 5. TABLE 1. Composite Amplifier Measured Performance AV R1 Ω R2 Ω C2 pF BW MHz SR en p-p (V/µs) (mVPP) 50 200 10k 8 3.3 178 37 100 100 10k 10 2.5 174 70 100 1k 100k 0.67 3.1 170 70 500 200 100k 1.75 1.4 96 250 1000 100 100k 2.2 0.98 64 400 In terms of the measured output peak-to-peak noise, the following relationship holds between output noise voltage, en p-p, for different closed-loop gain, AV, settings, where −3 dB Bandwidth is BW: 20132921 FIGURE 7. www.national.com 12 LMP2014MT Application Information 1/f corner frequency = 100 Hz AV = 2000 (Continued) LMP2014 AS ADC INPUT AMPLIFIER Measurement time = 100 sec Bandwidth = 2 Hz The LMP2014 is a great choice for an amplifier stage immediately before the input of an ADC (Analog-to-Digital Converter), whether AC or DC coupled. See Figure 7 and Figure 8. This is because of the following important characteristics: A) Very low offset voltage and offset voltage drift over time and temperature allow a high closed-loop gain setting without introducing any short-term or long-term errors. For example, when set to a closed-loop gain of 100 as the analog input amplifier for a 12-bit A/D converter, the overall conversion error over full operation temperature and 30 years life of the part (operating at 50˚C) would be less than 5 LSBs. This example will result in about 2.2 mVPP (1.9 LSB) of output noise contribution due to the op amp alone, compared to about 594 µVPP (less than 0.5 LSB) when that op amp is replaced with the LMP2014 which has no 1/f contribution. If the measurement time is increased from 100 seconds to 1 hour, the improvement realized by using the LMP2014 would be a factor of about 4.8 times (2.86 mVPP compared to 596 µV when LMP2014 is used) mainly because the LMP2014 accuracy is not compromised by increasing the observation time. D) Copper leadframe construction minimizes any thermocouple effects which would degrade low level/high gain data conversion application accuracy (see discussion under "The Benefits of the LMP2014" section above). E) Rail-to-Rail output swing maximizes the ADC dynamic range in 5-Volt single-supply converter applications. Below are some typical block diagrams showing the LMP2014 used as an ADC amplifier (Figure 7 and Figure 8). B) Fast large-signal settling time to 0.01% of final value (1.4 µs) allows 12 bit accuracy at 100 KHZ or more sampling rate. C) No flicker (1/f) noise means unsurpassed data accuracy over any measurement period of time, no matter how long. Consider the following op amp performance, based on a typical low-noise, high-performance commerciallyavailable device, for comparison: Op amp flatband noise = 8nV/ 20132922 FIGURE 8. 13 www.national.com LMP2014MT Quad High Precision, Rail-to-Rail Output Operational Amplifier Physical Dimensions inches (millimeters) unless otherwise noted 14-Pin TSSOP NS Package Number MTC14 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. 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