LMC660_06

LMC660 CMOS Quad Operational Amplifier June 2006 LMC660 CMOS Quad Operational Amplifier General Description The LMC660 CMOS Quad operational amplifier is ideal for operation from a single supply. It operates from +5V to +15.5V and features rail-to-rail output swing in addition to an input common-mode range that includes ground. Performance limitations that have plagued CMOS amplifiers in the past are not a problem with this design. Input VOS, drift, and broadband noise as well as voltage gain into realistic loads (2 kΩ and 600Ω) are all equal to or better than widely accepted bipolar equivalents. This chip is built with National’s advanced Double-Poly Silicon-Gate CMOS process. See the LMC662 datasheet for a dual CMOS operational amplifier with these same features. n n n n n n n n Low input offset voltage: 3 mV Low offset voltage drift: 1.3 µV/˚C Ultra low input bias current: 2 fA Input common-mode range includes V− Operating range from +5V to +15.5V supply ISS = 375 µA/amplifier; independent of V+ Low distortion: 0.01% at 10 kHz Slew rate: 1.1 V/µs Applications n n n n n n n n High-impedance buffer or preamplifier Precision current-to-voltage converter Long-term integrator Sample-and-Hold circuit Peak detector Medical instrumentation Industrial controls Automotive sensors Features n Rail-to-rail output swing n Specified for 2 kΩ and 600Ω loads n High voltage gain: 126 dB Connection Diagram 14-Pin SOIC/MDIP LMC660 Circuit Topology (Each Amplifier) 00876704 00876701 © 2006 National Semiconductor Corporation DS008767 www.national.com LMC660 Absolute Maximum Ratings (Note 3) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Differential Input Voltage Supply Voltage Output Short Circuit to V+ Output Short Circuit to V− Lead Temperature (Soldering, 10 sec.) Storage Temp. Range Voltage at Input/Output Pins Current at Output Pin Current at Input Pin Current at Power Supply Pin + − Power Dissipation Junction Temperature ESD tolerance (Note 8) (Note 2) 150˚C 1000V ± Supply Voltage 16V (Note 11) (Note 1) 260˚C −65˚C to +150˚C (V ) + 0.3V, (V ) − 0.3V Operating Ratings Temperature Range LMC660AI LMC660C Supply Voltage Range Power Dissipation Thermal Resistance (θJA) (Note 10) 14-Pin SOIC 14-Pin MDIP 115˚C/W 85˚C/W −40˚C ≤ TJ ≤ +85˚C 0˚C ≤ TJ ≤ +70˚C 4.75V to 15.5V (Note 9) ± 18 mA ± 5 mA 35 mA DC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C. Boldface limits apply at the temperature extremes. V+ = 5V, V− = 0V, VCM = 1.5V, VO = 2.5V and RL > 1MΩ unless otherwise specified. Parameter Conditions Typ (Note 4) LMC660AI Limit (Note 4) Input Offset Voltage Input Offset Voltage Average Drift Input Bias Current Input Offset Current Input Resistance Common Mode Rejection Ratio Positive Power Supply Rejection Ratio Negative Power Supply Rejection Ratio Input Common-Mode Voltage Range V+ = 5V & 15V For CMRR ≥ 50 dB V+ − 1.9 Large Signal Voltage Gain RL = 2 kΩ (Note 5) Sourcing Sinking RL = 600Ω (Note 5) Sourcing Sinking 250 500 1000 2000 −0.4 0V ≤ VCM ≤ 12.0V V = 15V 5V ≤ V+ ≤ 15V VO = 2.5V 0V ≤ V− ≤ −10V 94 83 + LMC660C Limit (Note 4) 6 6.3 Units 1 1.3 0.002 3 3.3 mV max µV/˚C pA 4 0.001 2 2 1 63 62 63 62 74 73 −0.1 0 V+ − 2.3 V+ − 2.4 300 200 90 80 150 100 50 40 max pA max TeraΩ dB min dB min dB min V max V min V/mV min V/mV min V/mV min V/mV min >1 83 70 68 70 68 84 83 −0.1 0 V+ − 2.3 V+ − 2.5 440 400 180 120 220 200 100 60 www.national.com 2 LMC660 DC Electrical Characteristics Parameter (Continued) Unless otherwise specified, all limits guaranteed for TJ = 25˚C. Boldface limits apply at the temperature extremes. V+ = 5V, V− = 0V, VCM = 1.5V, VO = 2.5V and RL > 1MΩ unless otherwise specified. Conditions Typ (Note 4) LMC660AI Limit (Note 4) LMC660C Limit (Note 4) 4.78 4.76 0.19 0.21 4.27 4.21 0.63 0.69 14.37 14.32 0.44 0.48 12.92 12.76 1.45 1.58 13 11 13 11 23 21 23 20 2.7 2.9 V min V max V min V max V min V max V min V max mA min mA min mA min mA min mA max Units Output Swing V+ = 5V RL = 2 kΩ to V /2 + 4.87 0.10 4.82 4.79 0.15 0.17 4.41 4.31 0.50 0.56 14.50 14.44 0.35 0.40 13.35 13.15 1.16 1.32 16 14 16 14 28 25 28 24 2.2 2.6 V+ = 5V RL = 600Ω to V /2 + 4.61 0.30 V+ = 15V RL = 2 kΩ to V+/2 14.63 0.26 V+ = 15V RL = 600Ω to V+/2 13.90 0.79 Output Current V+ = 5V Sourcing, VO = 0V Sinking, VO = 5V 22 21 40 39 1.5 Output Current V+ = 15V Sourcing, VO = 0V Sinking, VO = 13V (Note 11) Supply Current All Four Amplifiers VO = 1.5V AC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C. Boldface limits apply at the temperature extremes. V+ = 5V, V− = 0V, VCM = 1.5V, VO = 2.5V and RL > 1MΩ unless otherwise specified. Parameter Conditions Typ (Note 4) LMC660AI Limit (Note 4) Slew Rate Gain-Bandwidth Product Phase Margin Gain Margin Amp-to-Amp Isolation Input Referred Voltage Noise Input Referred Current Noise (Note 7) F = 1 kHz f = 1 kHz (Note 6) 1.1 1.4 50 17 130 22 0.0002 0.8 0.6 LMC660C Limit (Note 4) 0.8 0.7 V/µs min MHz Deg dB dB Units 3 www.national.com LMC660 AC Electrical Characteristics Parameter (Continued) Unless otherwise specified, all limits guaranteed for TJ = 25˚C. Boldface limits apply at the temperature extremes. V+ = 5V, V− = 0V, VCM = 1.5V, VO = 2.5V and RL > 1MΩ unless otherwise specified. Conditions Typ (Note 4) LMC660AI Limit (Note 4) LMC660C Limit (Note 4) % Units Total Harmonic Distortion f = 10 kHz, AV = −10 RL = 2 kΩ, VO = 8 VPP V+ = 15V 0.01 Note 1: Applies to both single supply and split supply operation. Continuous short circuit operation at elevated ambient temperature and/or multiple Op Amp shorts can result in exceeding the maximum allowed junction temperature of 150˚C. Output currents in excess of ± 30 mA over long term may adversely affect reliability. Note 2: 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. Note 3: 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 do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Note 4: Typical values represent the most likely parametric norm. Limits are guaranteed by testing or correlation. Note 5: V+ = 15V, VCM = 7.5V and RL connected to 7.5V. For Sourcing tests, 7.5V ≤ VO ≤ 11.5V. For Sinking tests, 2.5V ≤ VO ≤ 7.5V. Note 6: V+ = 15V. Connected as Voltage Follower with 10V step input. Number specified is the slower of the positive and negative slew rates. Note 7: Input referred. V+ = 15V and RL = 10 kΩ connected to V+/2. Each amp excited in turn with 1 kHz to produce VO = 13 VPP. Note 8: Human Body Model is 1.5 kΩ in series with 100 pF. Note 9: For operating at elevated temperatures the device must be derated based on the thermal resistance θJA with PD = (TJ − TA)/θJA. Note 10: All numbers apply for packages soldered directly into a PC board. Note 11: Do not connect output to V+ when V+ is greater than 13V or reliability may be adversely affected. Ordering Information Package Temperature Range Industrial −40˚C to +85˚C 14-Pin SOIC 14-Pin M DIP LMC660AIM LMC660AIMX LMC660AIN Commercial 0˚C to +70˚C LMC660CM LMC660CMX LMC660CN Rail Tape and Reel Rail M14A N14A Transport Media NSC Drawing www.national.com 4 LMC660 Typical Performance Characteristics Supply Current vs. Supply Voltage VS = ± 7.5V, TA = 25˚C unless otherwise specified. Offset Voltage 00876724 00876725 Input Bias Current Output Characteristics Current Sinking 00876726 00876727 Output Characteristics Current Sourcing Input Voltage Noise vs. Frequency 00876728 00876729 5 www.national.com LMC660 Typical Performance Characteristics VS = ±7.5V, TA = 25˚C unless otherwise specified. CMRR vs. Frequency Open-Loop Frequency Response (Continued) 00876730 00876731 Frequency Response vs. Capacitive Load Non-Inverting Large Signal Pulse Response 00876732 00876733 Stability vs. Capacitive Load Stability vs. Capacitive Load 00876734 00876735 www.national.com 6 LMC660 Application Hints AMPLIFIER TOPOLOGY The topology chosen for the LMC660, shown in Figure 1, is unconventional (compared to general-purpose op amps) in that the traditional unity-gain buffer output stage is not used; instead, the output is taken directly from the output of the integrator, to allow rail-to-rail output swing. Since the buffer traditionally delivers the power to the load, while maintaining high op amp gain and stability, and must withstand shorts to either rail, these tasks now fall to the integrator. As a result of these demands, the integrator is a compound affair with an embedded gain stage that is doubly fed forward (via Cf and Cff) by a dedicated unity-gain compensation driver. In addition, the output portion of the integrator is a push-pull configuration for delivering heavy loads. While sinking current the whole amplifier path consists of three gain stages with one stage fed forward, whereas while sourcing the path contains four gain stages with two fed forward. etc., and RP is the parallel combination of RF and RIN. This formula, as well as all formulae derived below, apply to inverting and non-inverting op amp configurations. When the feedback resistors are smaller than a few kΩ, the frequency of the feedback pole will be quite high, since CS is generally less than 10 pF. If the frequency of the feedback pole is much higher than the “ideal” closed-loop bandwidth (the nominal closed-loop bandwidth in the absence of CS), the pole will have a negligible effect on stability, as it will add only a small amount of phase shift. However, if the feedback pole is less than approximately 6 to 10 times the “ideal” −3 dB frequency, a feedback capacitor, CF, should be connected between the output and the inverting input of the op amp. This condition can also be stated in terms of the amplifier’s low-frequency noise gain: To maintain stability a feedback capacitor will probably be needed if where is the amplifier’s low-frequency noise gain and GBW is the amplifier’s gain bandwidth product. An amplifier’s lowfrequency noise gain is represented by the formula 00876704 FIGURE 1. LMC660 Circuit Topology (Each Amplifier) The large signal voltage gain while sourcing is comparable to traditional bipolar op amps, even with a 600Ω load. The gain while sinking is higher than most CMOS op amps, due to the additional gain stage; however, under heavy load (600Ω) the gain will be reduced as indicated in the Electrical Characteristics. Avoid resistive loads of less than 500Ω, as they may cause instability. COMPENSATING INPUT CAPACITANCE The high input resistance of the LMC660 op amps allows the use of large feedback and source resistor values without losing gain accuracy due to loading. However, the circuit will be especially sensitive to its layout when these large-value resistors are used. Every amplifier has some capacitance between each input and AC ground, and also some differential capacitance between the inputs. When the feedback network around an amplifier is resistive, this input capacitance (along with any additional capacitance due to circuit board traces, the socket, etc.) and the feedback resistors create a pole in the feedback path. In the following General Operational Amplifier circuit,Figure 2 the frequency of this pole is regardless of whether the amplifier is being used in inverting or non-inverting mode. Note that a feedback capacitor is more likely to be needed when the noise gain is low and/or the feedback resistor is large. If the above condition is met (indicating a feedback capacitor will probably be needed), and the noise gain is large enough that: the following value of feedback capacitor is recommended: If the feedback capacitor should be: where CS is the total capacitance at the inverting input, including amplifier input capacitance and any stray capacitance from the IC socket (if one is used), circuit board traces, 7 www.national.com LMC660 Application Hints (Continued) Note that these capacitor values are usually significant smaller than those given by the older, more conservative formula: 00876705 FIGURE 3. Rx, Cx Improve Capacitive Load Tolerance Capacitive load driving capability is enhanced by using a pull up resistor to V+ (Figure 4). Typically a pull up resistor conducting 500 µA or more will significantly improve capacitive load responses. The value of the pull up resistor must be determined based on the current sinking capability of the amplifier with respect to the desired output swing. Open loop gain of the amplifier can also be affected by the pull up resistor (see Electrical Characteristics). 00876706 CS consists of the amplifier’s input capacitance plus any stray capacitance from the circuit board and socket. CF compensates for the pole caused by CS and the feedback resistors. FIGURE 2. General Operational Amplifier Circuit Using the smaller capacitors will give much higher bandwidth with little degradation of transient response. It may be necessary in any of the above cases to use a somewhat larger feedback capacitor to allow for unexpected stray capacitance, or to tolerate additional phase shifts in the loop, or excessive capacitive load, or to decrease the noise or bandwidth, or simply because the particular circuit implementation needs more feedback capacitance to be sufficiently stable. For example, a printed circuit board’s stray capacitance may be larger or smaller than the breadboard’s, so the actual optimum value for CF may be different from the one estimated using the breadboard. In most cases, the values of CF should be checked on the actual circuit, starting with the computed value. CAPACITIVE LOAD TOLERANCE Like many other op amps, the LMC660 may oscillate when its applied load appears capacitive. The threshold of oscillation varies both with load and circuit gain. The configuration most sensitive to oscillation is a unity-gain follower. See Typical Performance Characteristics. The load capacitance interacts with the op amp’s output resistance to create an additional pole. If this pole frequency is sufficiently low, it will degrade the op amp’s phase margin so that the amplifier is no longer stable at low gains. As shown in Figure 3, the addition of a small resistor (50Ω to 100Ω) in series with the op amp’s output, and a capacitor (5 pF to 10 pF) from inverting input to output pins, returns the phase margin to a safe value without interfering with lowerfrequency circuit operation. Thus larger values of capacitance can be tolerated without oscillation. Note that in all cases, the output will ring heavily when the load capacitance is near the threshold for oscillation. 00876723 FIGURE 4. Compensating for Large Capacitive Loads with a Pull Up Resistor PRINTED-CIRCUIT-BOARD LAYOUT FOR HIGH-IMPEDANCE WORK It is generally recognized that any circuit which must operate with less than 1000 pA of leakage current requires special layout of the PC board. When one wishes to take advantage of the ultra-low bias current of the LMC662, typically less than 0.04 pA, it is essential to have an excellent layout. Fortunately, the techniques for obtaining low leakages are quite simple. First, the user must not ignore the surface leakage of the PC board, even though it may sometimes appear acceptably low, because under conditions of high humidity or dust or contamination, the surface leakage will be appreciable. To minimize the effect of any surface leakage, lay out a ring of foil completely surrounding the LMC660’s inputs and the terminals of capacitors, diodes, conductors, resistors, relay terminals, etc. connected to the op amp’s inputs. SeeFigure 5. To have a significant effect, guard rings should be placed on both the top and bottom of the PC board. This PC foil must then be connected to a voltage which is at the same voltage as the amplifier inputs, since no leakage current can flow between two points at the same potential. For example, a PC board trace-to-pad resistance of 1012Ω, which is normally considered a very large resistance, could leak 5 pA if the trace were a 5V bus adjacent to the pad of an input. This would cause a 100 times degradation from the LMC660’s actual performance. However, if a guard ring is held within 5 mV of the inputs, then even a resistance of 1011Ω would 8 www.national.com LMC660 Application Hints (Continued) cause only 0.05 pA of leakage current, or perhaps a minor (2:1) degradation of the amplifier’s performance. See Figure 6a,Figure 6b, Figure 6c for typical connections of guard rings for standard op amp configurations. If both inputs are active and at high impedance, the guard can be tied to ground and still provide some protection; see Figure 6d. 00876717 (a) Inverting Amplifier 00876718 (b) Non-Inverting Amplifier 00876716 FIGURE 5. Example, using the LMC660, of Guard Ring in P.C. Board Layout 00876719 (c) Follower 00876720 (d) Howland Current Pump FIGURE 6. Guard Ring Connections The designer should be aware that when it is inappropriate to lay out a PC board for the sake of just a few circuits, there is another technique which is even better than a guard ring on a PC board: Don’t insert the amplifier’s input pin into the board at all, but bend it up in the air and use only air as an insulator. Air is an excellent insulator. In this case you may have to forego some of the advantages of PC board construction, but the advantages are sometimes well worth the effort of using point-to-point up-in-the-air wiring. See Figure 7. 9 www.national.com LMC660 Application Hints (Continued) A suitable capacitor for C2 would be a 5 pF or 10 pF silver mica, NPO ceramic, or air-dielectric. When determining the magnitude of Ib−, the leakage of the capacitor and socket must be taken into account. Switch S2 should be left shorted most of the time, or else the dielectric absorption of the capacitor C2 could cause errors. Similarly, if S1 is shorted momentarily (while leaving S2 shorted) where Cx is the stray capacitance at the + input. 00876721 (Input pins are lifted out of PC board and soldered directly to components. All other pins connected to PC board.) FIGURE 7. Air Wiring BIAS CURRENT TESTING The test method of Figure 7 is appropriate for bench-testing bias current with reasonable accuracy. To understand its operation, first close switch S2 momentarily. When S2 is opened, then 00876722 FIGURE 8. Simple Input Bias Current Test Circuit www.national.com 10 LMC660 Typical Single-Supply Applications (V+ = 5.0 VDC) Additional single-supply applications ideas can be found in the LM324 datasheet. The LMC660 is pin-for-pin compatible with the LM324 and offers greater bandwidth and input resistance over the LM324. These features will improve the performance of many existing single-supply applications. Note, however, that the supply voltage range of the LMC660 is smaller than that of the LM324. Low-Leakage Sample-and-Hold Sine-Wave Oscillator 00876707 00876709 Instrumentation Amplifier Oscillator frequency is determined by R1, R2, C1, and C2: fosc = 1/2πRC, where R = R1 = R2 and C = C1 = C2. This circuit, as shown, oscillates at 2.0 kHz with a peak-topeak output swing of 4.5V. 1 Hz Square-Wave Oscillator 00876708 If R1 = R5, R3 = R6, and R4 = R7; then 00876710 Power Amplifier ∴ AV ≈100 for circuit shown. For good CMRR over temperature, low drift resistors should be used. Matching of R3 to R6 and R4 to R7 affect CMRR. Gain may be adjusted through R2. CMRR may be adjusted through R7. 00876711 11 www.national.com LMC660 Typical Single-Supply Applications (V+ = 5.0 VDC) (Continued) 10 Hz Bandpass Filter High Gain Amplifier with Offset Voltage Reduction 00876712 fO = 10 Hz Q = 2.1 Gain = −8.8 00876715 10 Hz High-Pass Filter Gain = −46.8 Output offset voltage reduced to the level of the input offset voltage of the bottom amplifier (typically 1 mV). 00876713 fc = 10 Hz d = 0.895 Gain = 1 2 dB passband ripple 1 Hz Low-Pass Filter (Maximally Flat, Dual Supply Only) 00876714 fc = 1 Hz d = 1.414 Gain = 1.57 www.national.com 12 LMC660 Physical Dimensions inches (millimeters) unless otherwise noted 14-Pin SOIC NS Package Number M14A 14-Pin MDIP NS Package Number N14A 13 www.national.com LMC660 CMOS Quad Operational Amplifier 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. 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