LMV791 17 MHz, Low Noise, CMOS Input, 1.8V Operational Amplifier General Description Features The LMV791 low noise, CMOS input operational amplifier while offers a low input voltage noise density of 5.8 nV/ consuming only 1.15 mA of quiescent current. The LMV791 is a unity gain stable op amp and has a gain bandwidth of 17 MHz. The LMV791 has a supply voltage range of 1.8V to 5.5V and can operate from a single supply. The LMV791 features a rail-to-rail output stage capable of driving a 600Ω load and sourcing as much as 60 mA of current. (Typical 5V supply, unless otherwise noted) n Input referred voltage noise 5.8 nV/ n Input bias current 0.1 pA n Unity gain bandwidth 17 MHz n Supply current 1.15 mA n Guaranteed 2.5V and 5.0V performance n Rail-to-rail output swing — @ 10 kΩ load 25 mV from rail 35 mV from rail — @ 2 kΩ load n Total harmonic distortion 0.01% @1 kHz, 600Ω n Temperature range −40oC to 125oC The LMV791 provides optimal performance in low voltage and low noise systems. A CMOS input stage, with typical input bias currents in the range of a few femtoAmperes, and an input common mode voltage range which includes ground make the LMV791 ideal for low power sensor applications. The LMV791 has a built-in enable feature which can be used to optimize power dissipation in low power applications. The LMV791 is manufactured using National’s advanced VIP50 process and is available in a 6-pin TSOT23 package. Applications n n n n n Photodiode Amplifiers Active filters and buffers Low noise signal processing Medical Instrumentation Sensor interface applications Typical Application 20116869 Photodiode Transimpedance Amplifier 20116839 Input Referred Voltage Noise vs. Frequency © 2005 National Semiconductor Corporation DS201168 www.national.com LMV791 17 MHz, Low Noise, CMOS Input, 1.8V Operational Amplifier September 2005 LMV791 Absolute Maximum Ratings (Note 1) Soldering Information If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Infrared or Convection (20 sec) 235˚C Wave Soldering Lead Temp (10 sec) 260˚C ESD Tolerance (Note 2) ± 2000V ± 200V Human Body Machine Model VIN Differential 0.3V Supply Voltage (V+ – V−) 6.0V Input/Output Pin Voltage Storage Temperature Range Operating Ratings (Note 1) Temperature Range (Note 3) + Supply Voltage (V – V ) −40˚C ≤ TA ≤ 125˚C V+ +0.3V, V− −0.3V 2V to 5.5V 0˚C ≤ TA ≤ 125˚C −65˚C to 150˚C Junction Temperature (Note 3) −40˚C to 125˚C − 1.8V to 5.5V Package Thermal Resistance (θJA (Note 3)) +150˚C 6-Pin TSOT23 170˚C/W 2.5V Electrical Characteristics Unless otherwise specified, all limits are guaranteed for TA = 25˚C, V+ = 2.5V, V− = 0V, VCM = V+/2, VEN = V+. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min (Note 5) Typ (Note 4) Max (Note 5) 0.1 ± 1.35 ± 1.65 VOS Input Offset Voltage TC VOS Input Offset Average Drift (Note 6) 1.0 IB Input Bias Current VCM = 1.0V (Notes 7, 8) 0.05 IOS Input Offset Current (Note 8) CMRR Common Mode Rejection Ratio 0V ≤ VCM ≤ 1.4V 80 75 94 PSRR Power Supply Rejection Ratio 2V ≤ V+ ≤ 5.5V, VCM = 0V 80 75 100 1.8V ≤ V+ ≤ 5.5V, VCM = 0V 80 98 CMRR ≥ 60 dB CMRR ≥ 55 dB AVOL Large Signal Voltage Gain VOUT = 0.15V to 2.2V, RLOAD = 2 kΩ to V+/2 85 80 98 VOUT = 0.15V to 2.2V, RLOAD = 10 kΩ to V+/2 88 84 110 RLOAD = 2 kΩ to V+/2 75 82 25 RLOAD = 10 kΩ to V+/2 65 71 20 Output Swing Low IOUT IS Output Short Circuit Current Supply Current per Amplifier www.national.com 0.5 50 −0.3 -0.3 + pA fA dB dB Input Common-Mode Voltage Range Output Swing High mV µV/˚C 10 CMVR VOUT Units 1.5 1.5 dB RLOAD = 2 kΩ to V /2 30 75 78 RLOAD = 10 kΩ to V+/2 15 65 67 Sourcing to V− VIN = 200 mV (Note 9) 35 28 47 Sinking to V+ VIN = –200 mV (Note 9) 7 5 15 V mV from rail mA Enable Mode VEN > 2.1 0.95 1.30 1.65 mA Shutdown Mode VEN < 0.4 0.02 1 5 µA 2 SR Slew Rate LMV791 2.5V Electrical Characteristics (Continued) AV = +1, Rising (10% to 90%) 8.5 AV = +1, Falling (90% to 10%) 10.5 V/µs GBWP Gain Bandwidth Product en Input-Referred Voltage Noise f = 1 kHz 6.2 14 nV/ in Input-Referred Current Noise f = 1 kHz 0.01 pA/ ton Turn-on Time 140 ns toff Turn-off Time 1000 ns VEN Enable Pin Voltage Range Enable Mode Shutdown Mode IEN THD+N Enable Pin Input Current Total Harmonic Distortion + Noise 2.1 to 2.5 2 to 2.5 0 to 0.4 0 to 0.5 Enable Mode VEN > 2.1V (Note 7) MHz V 1.5 3 Shutdown Mode VEN < 0.4V (Note 7) 0.003 0.1 f = 1 kHz, AV = 1, RLOAD = 600Ω 0.01 µA % 5V Electrical Characteristics Unless otherwise specified, all limits guaranteed for TA = 25˚C, V+ = 5V, V− = 0V, VCM = V+/2, VEN = V+. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min (Note 5) Typ (Note 4) Max (Note 5) 0.1 ± 1.35 ± 1.65 VOS Input Offset Voltage TC VOS Input Offset Average Drift (Note 6) 1.0 IB Input Bias Current VCM = 2.0V (Notes 7, 8) 0.1 IOS Input Offset Current (Note 8) CMRR Common Mode Rejection Ratio 0V ≤ VCM ≤ 3.7V 80 75 100 PSRR Power Supply Rejection Ratio 2V ≤ V+ ≤ 5.5V, VCM = 0V 80 75 100 80 98 1.8V ≤ V ≤ 5.5V, VCM = 0V Input Common-Mode Voltage Range CMRR ≥ 60 dB CMRR ≥ 55 dB AVOL Large Signal Voltage Gain VOUT = 0.3V to 4.7V, RLOAD = 2 kΩ to V+/2 85 80 97 VOUT = 0.3V to 4.7V, RLOAD = 10 kΩ to V+/2 88 84 110 RLOAD = 2 kΩ to V+/2 75 82 35 RLOAD = 10 kΩ to V+/2 65 71 25 Output Swing High Output Swing Low IOUT IS Output Short Circuit Current Supply Current per Amplifier pA fA dB dB CMVR VOUT mV µV/˚C 1 100 10 + Units −0.3 -0.3 4 4 dB RLOAD = 2 kΩ to V+/2 50 75 78 RLOAD = 10 kΩ to V+/2 20 65 67 Sourcing to V− VIN = 200 mV (Note 9) 45 37 60 Sinking to V+ VIN = –200 mV (Note 9) 10 6 21 V mV from rail mA Enable Mode (VEN > 4.6 V) 1.15 1.40 1.75 mA Shutdown Mode (VEN < 0.4V) 0.14 1 5 µA 3 www.national.com LMV791 5V Electrical Characteristics SR Slew Rate (Continued) AV = +1, Rising (10% to 90%) 6.0 9.5 AV = +1, Falling (90% to 10%) 7.5 11.5 V/µs GBWP Gain Bandwidth Product en Input - Referred Voltage Noise f = 1 kHz 5.8 in Input-Referred Current Noise f = 1 kHz 0.01 ton Turn-on Time 110 ns toff Turn-off Time 800 ns VEN Enable Pin Voltage Range IEN Enable Pin Input Current THD+N Total Harmonic Distortion + Noise 17 Enable Mode 4.6 to 5 4.5 to 5 Shutdown Mode 0 to 0.4 0 to 0.5 Enable Mode VEN > 4.6V (Note 7) MHz nV/ pA/ V 5.6 10 Shutdown Mode VEN < 0.4V (Note 7) 0.005 0.2 f = 1 kHz, AV = 1, RLOAD = 600Ω 0.01 µA % 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. 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 parametric norm at the time of characterization. Note 5: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlations using the statistical quality control (SQC) method. Note 6: Offset voltage average drift is determined by dividing the change in VOS by temperature change. Note 7: Positive current corresponds to current flowing into the device. Note 8: Input bias current and input offset current are guaranteed by design Note 9: The short circuit test is a momentary test, the short circuit duration is 1.5 ms. Connection Diagram 6-Pin TSOT23 20116801 Top View Ordering Information Package Part Number Package Marking Transport Media NSC Drawing 6-Pin TSOT23 LMV791MK AS1A 1k Units Tape and Reel MK06A LMV791MKX www.national.com 3k Units Tape and Reel 4 + Voltage = 5V, VCM = V /2, VEN = V Unless otherwise specified, TA = 25˚C, V– =0, V+ = Supply + Supply Current vs. Supply Voltage Supply Current vs. Supply Voltage in Shutdown Mode 20116805 20116806 VOS vs. VCM VOS vs. VCM 20116851 20116809 VOS vs. VCM VOS vs. Supply Voltage 20116811 20116812 5 www.national.com LMV791 Typical Performance Characteristics LMV791 Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, V–=0, V+ = Supply Voltage = 5V, VCM = V+/2, VEN = V+ (Continued) Positive Output Swing vs. Supply Voltage Negative Output Swing vs. Supply Voltage 20116817 20116815 Positive Output Swing vs. Supply Voltage Negative Output Swing vs. Supply Voltage 20116816 20116814 Positive Output Swing vs. Supply Voltage Negative Output Swing vs. Supply Voltage 20116813 20116818 www.national.com 6 Voltage = 5V, VCM = V+/2, VEN = V+ (Continued) Sourcing Current vs. Supply Voltage Sinking Current vs. Supply Voltage 20116820 20116819 Sourcing Current vs. Output Voltage Sinking Current vs. Output Voltage 20116850 20116854 Supply Current vs. Enable Pin Voltage Supply Current vs. Enable Pin Voltage 20116807 20116808 7 www.national.com LMV791 Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, V–=0, V+ = Supply LMV791 Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, V–=0, V+ = Supply Voltage = 5V, VCM = V+/2, VEN = V+ (Continued) Input Bias Current vs. VCM Input Bias Current vs. VCM 20116862 20116863 Input Referred Voltage Noise vs. Frequency THD+N vs. Peak-to-Peak Output Voltage (VOUT) 20116839 20116826 THD+N vs. Peak-to-Peak Output Voltage (VOUT) THD+N vs. Frequency 20116857 20116804 www.national.com 8 Voltage = 5V, VCM = V+/2, VEN = V+ (Continued) THD+N vs. Frequency Slew Rate vs. Supply Voltage 20116855 20116829 Open Loop Gain and Phase with Capacitive Load Open Loop Gain and Phase with Resistive Load 20116873 20116841 Overshoot and Undershoot vs. CLOAD Closed Loop Output Impedance vs. Frequency 20116832 20116830 9 www.national.com LMV791 Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, V–=0, V+ = Supply LMV791 Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, V–=0, V+ = Supply Voltage = 5V, VCM = V+/2, VEN = V+ (Continued) Small Signal Transient Response, AV=+1 Large Signal Transient Response, AV=+1 20116838 20116837 Small Signal Transient Response, AV=+1 Large Signal Transient Response, AV=+1 20116834 20116833 Phase Margin vs. Capacitive Load (Stability) Phase Margin vs. Capacitive Load (Stability) 20116845 20116846 www.national.com 10 Voltage = 5V, VCM = V+/2, VEN = V+ (Continued) Positive PSRR vs. Frequency Negative PSRR vs. Frequency 20116828 20116827 CMRR vs. Frequency 20116856 11 www.national.com LMV791 Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, V–=0, V+ = Supply LMV791 CAPACITIVE LOAD TOLERANCE Application Notes The LMV791 can directly drive 120 pF in unity-gain without oscillation. The unity-gain follower is the most sensitive configuration to capacitive loading. Direct capacitive loading reduces the phase margin of amplifiers. The combination of the amplifier’s output impedance and the capacitive load induces phase lag. This results in either an underdamped pulse response or oscillation. To drive a heavier capacitive load, the circuit in Figure 1 can be used. In Figure 1, the isolation resistor RISO and the load capacitor CL form a pole to increase stability by adding more phase margin to the overall system. The desired performance depends on the value of RISO. The bigger the RISO resistor value, the more stable VOUT will be. Increased RISO would, however, result in a reduced output swing and short circuit current. ADVANTAGES OF THE LMV791 Wide Bandwidth at Low Supply Current The LMV791 is a high performance op amp that provides a unity gain bandwidth of 17 MHz while drawing a low supply current of merely 1.15 mA. This makes it ideal for providing wideband amplification in portable applications. The enable and shutdown feature can also be used to design more power efficient systems and obtain wider bandwidth and better performance while using less power. Low Input Referred Noise and Low Input Bias Current The LMV791 has a very low input referred voltage noise at 1 kHz). A CMOS input stage ensures density (5.8 nV/ a small input bias current (100 fA) and, hence, the input ). This is referred current noise is very low (0.01 pA/ very helpful in maintaining signal fidelity, and makes the LMV791 ideal for audio and sensor based applications. Low Supply Voltage LMV791 is guaranteed to perform at 2.5V and 5V supply. The LMV791 is guaranteed to be operational at all supply voltages between 2V and 5.5V, for ambient temperatures ranging from −40˚C to 125˚C, thus utilizing the entire battery lifetime. The LMV791 is also guaranteed to be operational at 1.8V supply voltage, for temperatures between 0˚C and 125˚C. This makes the LMV791 ideal for usage in lowvoltage commercial applications. 20116861 FIGURE 1. INPUT CAPACITANCE AND FEEDBACK CIRCUIT ELEMENTS The LMV791 has a very low input bias current (50 fA) and a low 1/f noise corner frequency (400 Hz), which makes it ideal for sensor applications. However, to obtain this performance a large CMOS input stage is used, which adds to the input capacitance. Though this does not affect the DC and low frequency performance, at higher frequencies the input capacitance interacts with the input and the feedback impedances to create a pole, which results in lower phase margin and gain peaking. This can be controlled by being selective in the use of feedback resistors, as well as by using a feedback capacitance. For example, in the non-inverting amplifier shown in Figure 2, if CIN and CF are ignored and the open loop gain of the op amp is considered infinite then the gain of the circuit is −R2/R1. An op amp, however, usually has a dominant pole, which causes its gain to drop with frequency. Hence, this gain is only valid for DC and low frequency. To understand the effect of the input capacitance coupled with the non-ideal gain of the op amp, the circuit needs to be analyzed in the frequency domain using a Laplace transform. RRO and Ground Sensing Rail-to-rail output swing provides maximum possible dynamic range at the output. This is particularly important when operating at low supply voltages. An innovative positive feedback scheme is used to boost the current drive capability of the output stage. This allows the LMV791 to source more than 40 mA of current at 1.8V supply. This also limits the performance of the LMV791 as a comparator, and hence the usage of LMV791 in an open-loop configuration is not recommended. The input common-mode range includes the negative supply rail which allows direct sensing at ground in single supply operation. Enable and Shutdown Features The LMV791 is ideal for battery powered systems. With a low supply current of 1.15 mA and a shutdown current typically less than 1 µA, it allows the designer to maximize battery life. The enable pin of the LMV791 allows the op amp to be turned off and reduce its supply current to less than 1 uA. To power on the op amp the enable pin should be higher than V+ - 0.5V, where V+is the positive supply. To disable the op amp, the enable pin should be lesser than V− + 0.5V, where V−is the negative supply. Small Size The small footprint of the LMV791 package saves space on printed circuit boards, and enables the design of smaller electronic products, such as cellular phones, pagers, or other portable systems. Signals can pick up noise between the signal source and the amplifier. By using a physically smaller amplifier package, the LMV791 can be placed closer to the signal source, reducing noise pickup and increasing signal integrity. www.national.com 12 LMV791 Application Notes (Continued) 20116864 20116859 FIGURE 2. FIGURE 3. For simplicity, the op amp is modelled as an ideal integrator with a unity gain frequency of A0 . Hence, its transfer function (or gain) in the frequency domain is A0/s. Solving the circuit equations in the frequency domain, ignoring CF for the moment, results in an expression for the gain shown in Equation (1). A way of reducing the gain peaking is by adding a feedback capacitance CF in parallel with R2. This introduces another pole in the system and prevents the formation of pairs of complex conjugate poles which cause the gain to peak. Figure 4 shows the effect of CF on the frequency response of the circuit. Adding a capacitance of 2 pF removes the peak, while a capacitance of 5 pF creates a much lower pole and reduces the bandwidth excessively. (1) It can be inferred from the denominator of the transfer function that it has two poles, whose expressions can be obtained by solving for the roots of the denominator and are shown in Equation (2) (2) Equation (2) shows that as the values of R1 and R2 are increased, the magnitude of the poles, and hence the bandwidth of the amplifier, is reduced. This theory is verified by using different values of R1 and R2 in the circuit shown in Figure 1 and by comparing their frequency responses. In Figure 3 the frequency responses for three different values of R1 and R2 are shown. When both R1 and R2 are 1 kΩ, the response is flattest and widest; whereas, it narrows and peaks significantly when both their values are changed to 10 kΩ or 30 kΩ. So it is advisable to use lower values of R1 and R2 to obtain a wider and flatter response. Lower resistances also help in high sensitivity circuits since they add less noise. 20116860 FIGURE 4. AUDIO PRE-AMPLIFIER WITH BANDPASS FILTERING With low input referred voltage noise, low supply voltage and low supply current, and a low harmonic distortion, the LMV791 is ideal for audio applications. Its wide unity gain bandwidth allows it to provide large gain for a wide range of frequencies and it can be used to design a pre-amplifier to drive a load of as low as 600Ω with less than 0.01% distortion. Two amplifier circuits are shown in Figure 5 and Figure 6. Figure 5 is an inverting amplifier and provides a gain of −10, while Figure 6 is a non-inverting amplifier and provides a gain of 11. In either of these circuits, the coupling capacitor CC1 decides the lower frequency at which the circuit starts providing gain, while the feedback capacitor CF decides the 13 www.national.com LMV791 Application Notes TRANSIMPEDANCE AMPLIFIER (Continued) With a wide bandwidth, low input bias current and low input voltage and current noise, the LMV791 is ideal for wideband transimpedance applications. Figure 8 shows a photodiode transimpedance amplifier used in a number of applications such as barcode scanners, light meters, fiber optic receivers and industrial sensors. The key components are a photodiode, an op amp and a feedback resistor RF. The voltage around the photodiode is kept constant to avoid nonlinearities. The op amp converts the current flowing into the resistor RF into a voltage at its output, and hence provides the transimpedance gain. frequency at which the gain starts dropping off. Figure 7 shows the frequency response of the inverting amplifier with different values of CF. An interesting aspect of this type of amplifiers, also known as I-V converters, is that in most cases the frequency response of the circuit needs to be modified to prevent oscillations. The capacitance at the input of the op amp includes the diode parasitic capacitance CD as well as the op amp common-mode capacitance CCM. This high capacitance combines with a large RF, needed for a reasonable transimpedance gain, to create a phase shift around the loop, which results in oscillation at high frequencies. 20116865 FIGURE 5. 20116869 FIGURE 8. Photodiode Transimpedance Amplifier 20116866 A feedback capacitance CF is usually added in parallel with RF to maintain circuit stability and control the frequency response. To achieve a maximally flat, 2nd-order Butterworth response, the feedback pole (RF and CF) should be set using Equation (3). FIGURE 6. (3) Calculating CF from Equation (3) can sometimes return unreasonably small values ( < 2 pF), especially for high speed applications. In these cases, its often more practical to use the circuit shown in Figure 9 in order to allow more reasonable values. The new value of C’F is (1+ RB/RA) CF. This relationship holds as long as RA << RF 20116858 FIGURE 7. www.national.com 14 needs to have low voltage noise and low input bias current. Typical applications include Infra-red (IR) thermometry, thermocouple amplifiers and pH electrode buffers. Figure 10 is an example of a typical circuit used for measuring IR radiation intensity, often used for estimating the temperature of an object from a distance. The IR sensor generates a voltage proportional to I, the intensity of the IR radiation falling on it. The resistance RA and RB are selected to provide a high gain to amplify this voltage, while CF is added to filter out the high frequency noise. (Continued) 20116871 FIGURE 9. 20116872 SENSOR INTERFACES LMV791’s low input bias current and low input referred noise make it an ideal part for sensor interfaces. These circuits are required to sense voltages of the order of a few µV, and currents amounting to less than a nA, and hence the op amp FIGURE 10. IR Radiation Sensor 15 www.national.com LMV791 Application Notes LMV791 17 MHz, Low Noise, CMOS Input, 1.8V Operational Amplifier Physical Dimensions inches (millimeters) unless otherwise noted 6-Pin TSOT23 NS Package Number MK06A 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. 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