LMC6034 CMOS Quad Operational Amplifier General Description The LMC6034 is a CMOS quad operational amplifier which can operate from either a single supply or dual supplies. Its performance features include an input common-mode range that reaches ground, low input bias current, and high voltage gain into realistic loads, such as 2 kΩ and 600Ω. This chip is built with National’s advanced Double-Poly Silicon-Gate CMOS process. See the LMC6032 datasheet for a CMOS dual operational amplifier with these same features. For higher performance characteristics refer to the LMC660. Features n Specified for 2 kΩ and 600Ω loads n High voltage gain: 126 dB n n n n n n n n Low offset voltage drift: 2.3 µV/˚C Ultra low input bias current: 40 fA Input common-mode range includes V− Operating Range from +5V to +15V supply ISS = 400 µA/amplifier; independent of V+ Low distortion: 0.01% at 10 kHz Slew rate: 1.1 V/µs Improved performance over TLC274 Applications n n n n n High-impedance buffer or preamplifier Current-to-voltage converter Long-term integrator Sample-and-hold circuit Medical instrumentation Connection Diagram 14-Pin DIP/SO DS011134-1 Top View Ordering Information Temperature Range Package NSC Drawing Transport Media 14-Pin N14A Rail Industrial −40˚C ≤ TJ ≤ +85˚C LMC6034IN Molded DIP LMC6034IM 14-Pin Small Outline © 1999 National Semiconductor Corporation DS011134 M14A Rail Tape and Reel www.national.com LMC6034 CMOS Quad Operational Amplifier May 1998 Absolute Maximum Ratings (Note 1) Differential Input Voltage Supply Voltage (V+ − V−) Output Short Circuit to V+ Output Short Circuit to V− Lead Temperature (Soldering, 10 sec.) Storage Temperature Range Power Dissipation Voltage at Output/Input Pin Current at Output Pin ± 5 mA Current at Input Pin Current at Power Supply Pin Junction Temperature (Note 3) ESD Tolerance (Note 4) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. ± Supply Voltage 35 mA 150˚C 1000V Operating Ratings(Note 1) 16V (Note 10) (Note 2) −40˚C ≤ TJ ≤ +85˚C 4.75V to 15.5V (Note 11) Temperature Range Supply Voltage Range Power Dissipation Thermal Resistance (θJA), (Note 12) 14-Pin DIP 14-Pin SO 260˚C −65˚C to +150˚C (Note 3) (V+) +0.3V, (V−) −0.3V ± 18 mA 85˚C/W 115˚C/W DC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C. Boldface limits apply at the temperature extremes. V+ = 5V, V− = GND = 0V, VCM = 1.5V, VOUT = 2.5V, and RL > 1M unless otherwise specified. Symbol Parameter Conditions Typical (Note 5) LMC6034I Units Limit (Note 6) VOS ∆VOS/∆T Input Offset Voltage 1 Input Offset Voltage 9 mV 11 max 2.3 µV/˚C Average Drift IB IOS Input Bias Current Input Offset Current RIN Input Resistance CMRR Common Mode −PSRR 83 Rejection Ratio 5V ≤ V+ ≤ 15V VO = 2.5V Negative Power Supply 0V ≤ V− ≤ −10V 94 Rejection Ratio VCM Input Common-Mode V+ = 5V & 15V Voltage Range For CMRR ≥ 50 dB −0.4 V+ − 1.9 AV Large Signal Voltage Gain RL = 2 kΩ (Note 7) 2000 Sourcing 100 max pA TeraΩ 63 dB 60 min 63 dB 60 min 74 dB 70 min −0.1 V 0 max V+ − 2.3 V V+ − 2.6 min 200 V/mV 100 min V/mV Sinking 500 90 40 min RL = 600Ω (Note 7) 1000 100 V/mV Sourcing Sinking www.national.com max >1 83 Positive Power Supply pA 200 0.01 0V ≤ VCM ≤ 12V V+ = 15V Rejection Ratio +PSRR 0.04 250 2 75 min 50 V/mV 20 min DC Electrical Characteristics (Continued) Unless otherwise specified, all limits guaranteed for TJ = 25˚C. Boldface limits apply at the temperature extremes. V+ = 5V, V− = GND = 0V, VCM = 1.5V, VOUT = 2.5V, and RL > 1M unless otherwise specified. Symbol Parameter Conditions Typical (Note 5) LMC6034I Units Limit (Note 6) VO Output Voltage Swing V+ = 5V RL = 2 kΩ to 2.5V 4.87 0.10 V+ = 5V RL = 600Ω to 2.5V 4.61 0.30 V+ = 15V RL = 2 kΩ to 7.5V 14.63 0.26 V+ = 15V RL = 600Ω to 7.5V 13.90 0.79 IO Output Current V+ = 5V 22 Sourcing, VO = 0V Sinking, VO = 5V V+ = 15V 21 40 Sourcing, VO = 0V Sinking, VO = 13V 39 (Note 10) IS Supply Current All Four Amplifiers VO = 1.5V 3 1.5 4.20 V 4.00 min 0.25 V 0.35 max 4.00 V 3.80 min 0.63 V 0.75 max 13.50 V 13.00 min 0.45 V 0.55 max 12.50 V 12.00 min 1.45 V 1.75 max 13 mA 9 min 13 mA 9 min 23 mA 15 min 23 mA 15 min 2.7 mA 3.0 max www.national.com AC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C. Boldface limits apply at the temperature extremes. V+ = 5V, V− = GND = 0V, VCM = 1.5V, VOUT = 2.5V, and RL > 1M unless otherwise specified. Symbol Parameter Conditions Typical (Note 5) LMC6034I Units Limit (Note 6) SR Slew Rate (Note 8) 1.1 0.8 0.4 V/µs min GBW Gain-Bandwidth Product 1.4 MHz φM Phase Margin 50 Deg GM Gain Margin 17 dB 130 dB 0.0002 Amp-to-Amp Isolation en Input-Referred Voltage Noise (Note 9) F = 1 kHz in Input-Referred Current Noise F = 1 kHz THD Total Harmonic Distortion F = 10 kHz, AV = −10 RL = 2 kΩ, VO = 8 VPP 22 0.01 % ± 5V Supply Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component 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 2: 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 3: The maximum power dissipation is a function of TJ(max), θJA, TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ(max)–TA)/θJA. Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Note 5: Typical values represent the most likely parametric norm. Note 6: All limits are guaranteed at room temperature (standard type face) or at operating temperature extremes (bold type face). Note 7: 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 8: V+ = 15V. Connected as Voltage Follower with 10V step input. Number specified is the slower of the positive and negative slew rates. Note 9: 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 10: Do not connect output to V+, when V+ is greater than 13V or reliability may be adversely affected. Note 11: For operating at elevated temperatures the device must be derated based on the thermal resistance θJA with PD = (TJ − TA)/θJA. Note 12: All numbers apply for packages soldered directly into a PC board. Typical Performance Characteristics Supply Current vs Supply Voltage VS = ± 7.5V, TA = 25˚C unless otherwise specified Output Characteristics Current Sinking Input Bias Current DS011134-24 DS011134-25 DS011134-23 www.national.com 4 Typical Performance Characteristics Output Characteristics Current Sourcing VS = ± 7.5V, TA = 25˚C unless otherwise specified (Continued) Input Voltage Noise vs Frequency CMRR vs Frequency DS011134-29 DS011134-27 Open-Loop Frequency Response DS011134-28 Frequency Response vs Capacitive Load DS011134-30 Stability vs Capacitive Load Non-Inverting Large Signal Pulse Response DS011134-31 DS011134-32 Stability vs Capacitive Load DS011134-33 DS011134-34 Note: Avoid resistive loads of less than 500Ω, as they may cause instability. Applications Hint 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. Amplifier Topolgy The topology chosen for the LMC6034, 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 a larger 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. 5 www.national.com Applications Hint (Continued) is the amplifier’s low-frequency noise gain and GBW is the amplifier’s gain bandwidth product. An amplifier’s low-frequency noise gain is represented by the formula 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: DS011134-3 FIGURE 1. LMC6034 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. Compensating Input Capacitance The high input resistance of the LMC6034 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 the following value of feedback capacitor is recommended: If the feedback capacitor should be: Note that these capacitor values are usually significantly smaller than those given by the older, more conservative formula: where CS is the total capacitance at the inverting input, including amplifier input capcitance and any stray capacitance from the IC socket (if one is used), circuit board traces, 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 DS011134-4 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 ca- where www.national.com 6 Applications Hint PRINTED-CIRCUIT-BOARD LAYOUT FOR HIGH-IMPEDANCE WORK (Continued) pacitance, 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. 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 LMC6034, 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. Capacitive Load Tolerance Like many other op amps, the LMC6034 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 lower-frequency 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. To minimize the effect of any surface leakage, lay out a ring of foil completely surrounding the LMC6034’s inputs and the terminals of capacitors, diodes, conductors, resistors, relay terminals, etc. connected to the op-amp’s inputs. See Figure 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 LMC6034’s actual performance. However, if a guard ring is held within 5 mV of the inputs, then even a resistance of 1011Ω would cause only 0.05 pA of leakage current, or perhaps a minor (2:1) degradation of the amplifier’s performance. See Figures 6, 7, 8 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 9. DS011134-5 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). DS011134-6 FIGURE 5. Example of Guard Ring in P.C. Board Layout DS011134-22 FIGURE 4. Compensating for Large Capacitive Loads with a Pull Up Resistor 7 www.national.com Applications Hint 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 10. (Continued) DS011134-7 FIGURE 6. Guard Ring Connections Inverting Amplifier DS011134-11 (Input pins are lifted out of PC board and soldered directly to components. All other pins connected to PC board.) FIGURE 10. Air Wiring BIAS CURRENT TESTING The test method of Figure 11 is appropriate for bench-testing bias current with reasonable accuracy. To understand its operation, first close switch S2 momentarily. When S2 is opened, then DS011134-8 FIGURE 7. Guard Ring Connections Non-Inverting Amplifier DS011134-9 FIGURE 8. Guard Ring Connections Follower DS011134-12 FIGURE 11. Simple Input Bias Current Test Circuit 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) DS011134-10 FIGURE 9. Guard Ring Connections Howland Current Pump 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 where Cx is the stray capacitance at the + input. www.national.com 8 Typical Single-Supply Applications (V+ = 5.0 VDC) Additional single-supply applications ideas can be found in the LM324 datasheet. The LMC6034 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 LMC6034 is smaller than that of the LM324. Sine-Wave Oscillator Low-Leakage Sample-and-Hold DS011134-13 DS011134-15 Oscillator frequency is determined by R1, R2, C1, and C2: fosc = 1/2πRC, where R = R1 = R2 and C = C1 = C2. Instrumentation Amplifier This circuit, as shown, oscillates at 2.0 kHz with a peak-to-peak output swing of 4.0V. 1 Hz Square-Wave Oscillator DS011134-14 DS011134-16 Power Amplifier 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. DS011134-17 9 www.national.com Typical Single-Supply Applications 1 Hz Low-Pass Filter (Maximally Flat, Dual Supply Only) (V+ = 5.0 VDC) (Continued) 10 Hz Bandpass Filter DS011134-19 fc = 1 Hz d = 1.414 Gain = 1.57 DS011134-18 fO = 10 Hz Q = 2.1 Gain = −8.8 High Gain Amplifier with Offset Voltage Reduction 10 Hz High-Pass Filter DS011134-20 fc = 10 Hz d = 0.895 Gain = 1 2 dB passband ripple DS011134-21 Gain = −46.8 Output offset voltage reduced to the level of the input offset voltage of the bottom amplifier (typically 1 mV). www.national.com 10 Physical Dimensions inches (millimeters) unless otherwise noted Small Outline Dual-In-Line Pkg. (M) Order Number LMC6034IM NS Package Number M14A Molded Dual-In-Line Pkg. (N) Order Number LMC6034IN NS Package Number N14A 11 www.national.com LMC6034 CMOS Quad Operational Amplifier Notes 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 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. 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