LMV793 VIP50 MIL-STD-883 JESD22-A115-A JESD22-C101-C LMV793MF LMV793MFX - Datasheet Archive

 

88 MHz, Low Noise, 1.8V CMOS Input, Decompensated Operational Amplifier General Description Features The LMV793 CMOS input

 

LMV793 LMV793 88 MHz, Low Noise, 1.8V CMOS Input, Decompensated Operational Amplifier General Description Features The LMV793 LMV793 CMOS input operational amplifier offers a low while consuming input voltage noise density of 5.8 nV/ only 1.15 mA of quiescent current. The LMV793 LMV793 is stable at a gain of 10 and has a gain bandwidth product (GBW) of 88 MHz. The LMV793 LMV793 has a supply voltage range of 1.8V to 5.5V and can operate from a single supply. The LMV793 LMV793 features a rail-to-rail output stage capable of driving a 600 load and sourcing as much as 60 mA of current. The LMV793 LMV793 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 LMV793 LMV793 ideal for low power sensor applications where high speeds are needed. The LMV793 LMV793 is manufactured using National's advanced VIP50 VIP50 process and is offered in either a 5-pin SOT23 or an 8Pin SOIC package respectively. (Typical 5V supply, unless otherwise noted) 5.8 nV/ Input referred voltage noise 100 fA Input bias current 88 MHz Gain bandwidth product 1.15 mA Supply current per channel Rail-to-rail output swing 25 mV from rail - @ 10 k load 35 mV from rail - @ 2 k load Guaranteed 2.5V and 5.0V performance 0.01% @1 kHz, 600 Total harmonic distortion -40°C to 125°C Temperature range Applications ADC interface Photodiode amplifiers Active filters and buffers Low noise signal processing Medical instrumentation Sensor interface applications Typical Application 20216369 Photodiode Transimpedance Amplifier © 2007 National Semiconductor Corporation 202163 20216339 Input Referred Voltage Noise vs. Frequency www.national.com LMV793 LMV793 88 MHz, Low Noise, 1.8V CMOS Input, Decompensated Operational Amplifier March 2007 LMV793 LMV793 Soldering Information Absolute Maximum Ratings (Note 1) Infrared or Convection (20 sec) Wave Soldering Lead Temp (10 sec) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Operating Ratings ESD Tolerance (Note 2) Human Body Model Machine Model VIN Differential Supply Voltage (V+ ­ V-) Input/Output Pin Voltage Storage Temperature Range Junction Temperature (Note 3) 260°C (Note 1) Temperature Range (Note 3) Supply Voltage (V+ ­ V-) -40°C TA 125°C 2000V 200V ±0.3V 6.0V V+ +0.3V, V- -0.3V -65°C to 150°C +150°C 2.5V Electrical Characteristics 235°C -40°C to 125°C 2.0V to 5.5V 0°C TA 125°C 1.8V to 5.5V Package Thermal Resistance (JA (Note 3) 5-Pin SOT23 8-Pin SOIC 180°C/W 190°C/W (Note 4) Unless otherwise specified, all limits are guaranteed for TA = 25°C, V+ = 2.5V, V- = 0V, VCM = V+/2 = VO. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Input Offset Voltage TC VOS Input Offset Average Drift (Note 7) IB Input Bias Current VCM = 1.0V (Notes 8, 9) Typ (Note 5) Max (Note 6) 0.1 VOS Min (Note 6) ±1.35 ±1.65 -40°C TA 85°C Input Offset Current Power Supply Rejection Ratio 1 25 0.05 1 100 Common Mode Rejection Ratio 0V VCM 1.4V PSRR 0.05 -40°C TA 125°C CMRR (Note 9) 10 AVOL 2.0V V+ 5.5V, VCM = 0V 80 75 100 80 98 Input Common-Mode Voltage Range CMRR 60 dB Open Loop Gain VOUT = 0.15V to 2.2V, RL = 10 k to V+/2 110 dB 75 82 20 65 71 RL = 2 k to V+/2 30 75 78 15 65 67 Sourcing to V- VIN = 200 mV (Note 10) 35 28 7 5 15 Supply Current Per Amplifier www.national.com mV from rail 47 Sinking to V+ VIN = ­200 mV (Note 10) IS Output Short Circuit Current 25 RL = 10 k to V+/2 IOUT RL = 2 k to V+/2 RL = 10 k to V+/2 Output Swing Low V 98 88 84 VOUT = 0.15V to 2.2V, Output Swing High 1.5 1.5 85 80 V+/2 dB dB -0.3 -0.3 CMRR 55 dB RL = 2 k to VOUT pA fA 94 1.8V V+ 5.5V, VCM = 0V CMVR 80 75 mV V/°C -1.0 IOS Units 0.95 2 mA 1.30 1.65 mA Slew Rate AV = +10, Rising (10% to 90%) 40 AV = +10, Falling (90% to 10%) 28 V/s GBWP Gain Bandwidth Product AV = +10, RL = 10 k 88 en Input-Referred Voltage Noise f = 1 kHz 6.2 nV/ in Input-Referred Current Noise f = 1 kHz 0.01 pA/ THD+N Total Harmonic Distortion + Noise f = 1 kHz, AV = 1, RL = 600 0.01 5V Electrical Characteristics MHz % (Note 4) Unless otherwise specified, all limits are guaranteed for TA = 25°C, V+ = 5V, V- = 0V, VCM = V+/2 = VO. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Input Offset Voltage TC VOS Input Offset Average Drift (Note 7) IB Input Bias Current VCM = 2.0V (Notes 8, 9) Typ (Note 5) Max (Note 6) 0.1 VOS Min (Note 6) ±1.35 ±1.65 Input Offset Current CMRR Power Supply Rejection Ratio 0.1 1 25 0.1 1 100 Common Mode Rejection Ratio 0V VCM 3.7V PSRR -40°C TA 85°C (Note 9) 10 AVOL 2.0V V+ 5.5V, VCM = 0V 80 75 100 80 98 Input Common-Mode Voltage Range CMRR 60 dB Open Loop Gain VOUT = 0.3V to 4.7V, V 97 88 84 RL = 10 k to V+/2 Output Swing High 4 4 85 80 VOUT = 0.3V to 4.7V, dB dB -0.3 -0.3 CMRR 55 dB RL = 2 k to V+/2 VOUT 110 dB Output Short Circuit Current 35 75 82 25 65 71 RL = 2 k to V+/2 42 75 78 RL = 10 k to V+/2 IOUT RL = 2 k to V+/2 RL = 10 k to V+/2 Output Swing Low 20 65 67 Slew Rate 45 37 10 6 21 mV from rail 60 Supply Current per Amplifier SR Sourcing to V- VIN = 200 mV (Note 10) Sinking to V+ VIN = ­200 mV (Note 10) IS pA fA 100 1.8V V+ 5.5V, VCM = 0V CMVR 80 75 mV V/°C -1.0 -40°C TA 125°C IOS Units 1.15 AV = +10, Rising (10% to 90%) 40 AV = +10, Falling (90% to 10%) 28 GBWP Gain Bandwidth Product AV = +10, RL = 10 k 88 en Input-Referred Voltage Noise f = 1 kHz 5.8 3 mA 1.40 1.75 mA V/s MHz nV/ www.national.com LMV793 LMV793 SR LMV793 LMV793 in Input-Referred Current Noise f = 1 kHz 0.01 THD+N Total Harmonic Distortion + Noise f = 1 kHz, AV = 1, RL = 600 0.01 pA/ % 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, applicable std. MIL-STD-883 MIL-STD-883, Method 3015.7. Machine Model, applicable std. JESD22-A115-A JESD22-A115-A (ESD MM std. of JEDEC) Field-Induced Charge-Device Model, applicable std. JESD22-C101-C JESD22-C101-C (ESD FICDM std. of JEDEC). Note 3: The maximum power dissipation is a function of TJ(MAX), JA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ(MAX) - TA)/JA. All numbers apply for packages soldered directly onto a PC Board. Note 4: 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 such that TJ = TA. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self-heating where TJ > TA. Note 5: Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary over time and will also depend on the application and configuration. The typical values are not tested and are not guaranteed on shipped production material. Note 6: 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 7: Offset voltage average drift is determined by dividing the change in VOS by temperature change. Note 8: Positive current corresponds to current flowing into the device. Note 9: Input bias current and input offset current are guaranteed by design Note 10: The short circuit test is a momentary test, the short circuit duration is 1.5 ms. Connection Diagrams 5-Pin SOT23 8-Pin SOIC 20216301 Top View 20216385 Top View Ordering Information Package 5-Pin SOT23 8-Pin SOIC www.national.com Part Number LMV793MF LMV793MF LMV793MFX LMV793MFX LMV793MA LMV793MA LMV793MAX LMV793MAX Package Marking AS4A LMV793MA LMV793MA 4 Transport Media 1k Units Tape and Reel 3k Units Tape and Reel 95 Units/Rail 2.5k Units Tape and Reel NSC Drawing MF05A MF05A M08A Unless otherwise specified, TA = 25°C, V­ = 0, V+ = Supply Voltage Supply Current vs. Supply Voltage (LMV793 LMV793) Supply Current vs. Supply Voltage (LMV794 LMV794) 20216305 20216381 VOS vs. VCM VOS vs. VCM 20216351 20216309 VOS vs. VCM VOS vs. Supply Voltage 20216311 20216312 5 www.national.com LMV793 LMV793 Typical Performance Characteristics = 5V, VCM = V+/2. LMV793 LMV793 Slew Rate vs. Supply Voltage Input Bias Current vs. VCM 20216352 20216362 Input Bias Current vs. VCM Sourcing Current vs. Supply Voltage 20216387 20216320 Sinking Current vs. Supply Voltage Sourcing Current vs. Output Voltage 20216350 20216319 www.national.com 6 Positive Output Swing vs. Supply Voltage 20216317 20216354 Negative Output Swing vs. Supply Voltage Positive Output Swing vs. Supply Voltage 20216315 20216316 Negative Output Swing vs. Supply Voltage Positive Output Swing vs. Supply Voltage 20216314 20216318 7 www.national.com LMV793 LMV793 Sinking Current vs. Output Voltage LMV793 LMV793 Negative Output Swing vs. Supply Voltage Input Referred Voltage Noise vs. Frequency 20216339 20216313 Overshoot and Undershoot vs. CLOAD THD+N vs. Frequency 20216326 20216330 THD+N vs. Frequency THD+N vs. Peak-to-Peak Output Voltage (VOUT) 20216304 www.national.com 20216374 8 LMV793 LMV793 THD+N vs. Peak-to-Peak Output Voltage (VOUT) Open Loop Gain and Phase 20216306 20216375 Closed Loop Output Impedance vs. Frequency Small Signal Transient Response, AV = +10 20216353 20216332 Large Signal Transient Response, AV = +10 Small Signal Transient Response, AV = +10 20216355 20216357 9 www.national.com LMV793 LMV793 Large Signal Transient Response, AV = +10 PSRR vs. Frequency 20216363 20216370 CMRR vs. Frequency Input Common Mode Capacitance vs. VCM 20216356 www.national.com 20216376 10 ADVANTAGES OF THE LMV793 LMV793 Wide Bandwidth at Low Supply Current The LMV793 LMV793 is a high performance op amp that provides a GBW of 88 MHz with a gain of 10 while drawing a low supply current of 1.15 mA. This makes it ideal for providing wideband amplification in data acquisition applications. With the proper compensation the LMV793 LMV793 can be operated at gains of ±1 and still maintain much faster slew rates over the fully compensated amplifiers. The increase in bandwidth and slew rate is obtained without any additional power consumption over the LMV796 LMV796. Low Input Referred Noise and Low Input Bias Current The LMV793 LMV793 have 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 low input referred current noise (0.01 pA/ ). This is very helpful in maintaining signal integrity, and makes the LMV793 LMV793 ideal for audio and sensor based applications. Low Supply Voltage The LMV793 LMV793 has performance guaranteed at 2.5V and 5V supply. The LMV793 LMV793 is guaranteed to be operational at all supply voltages between 2.0V and 5.5V, for ambient temperatures ranging from -40°C to 125°C, thus utilizing the entire battery lifetime. The LMV793 LMV793 is also guaranteed to be operational at 1.8V supply voltage, for temperatures between 0°C and 125°C optimizing its usage in low-voltage applications. 20216322 FIGURE 1. LMV793 LMV793 AVOL vs. Frequency RRO and Ground Sensing Rail-to-rail output swing provides the maximum possible dynamic range. 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 LMV793 LMV793 to source more than 40 mA of current at 1.8V supply. This also limits the performance of the LMV793 LMV793 as a comparator, and hence the usage of the LMV793 LMV793 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. Small Size The small footprint of the LMV793 LMV793 package saves space on printed circuit boards, and enables the design of smaller electronic products, such as cellular phones, pagers, or other portable systems. Long traces between the signal source and the op amp make the signal path more susceptible to noise pick up. By using the physically smaller LMV793 LMV793 package, the op amp can be placed closer to the signal source, reducing noise pickup and maintaining signal integrity. 20216323 FIGURE 2. LMV796 LMV796 AVOL vs. Frequency Figure 1 shows the much larger bandwidth of the LMV793 LMV793 as compared to the LMV796 LMV796 shown in Figure 2, 88 MHz vs. 17 MHz; giving the decompensated LMV793 LMV793 five times the bandwidth of the LMV796 LMV796. What is a Decompensated Op Amp? The differences between the unity gain stable op amp and the decompensated op amp are shown in Figure 3 below. This Bode plot assumes an ideal two pole system. The dominant pole of the decompensate op amp is at a higher frequency, f1, as compared to the unity-gain stable op amp which is at fd as shown in Figure 3. This is done in order to increase the speed capability of the op amp while maintaining the same power dissipation of the unity gain stable op amp. The LMV793 LMV793 has a dominant pole at 8.6 Hz. The unity gain stable LMV796 LMV796 has its dominant pole at 1.6 Hz. USING THE DECOMPENSATED LMV793 LMV793 Advantages of Decompensated Op Amps A fully compensated op amp is designed to operate with good stability down to gains of ±1. This large amount of compensation does provide an op amp that is relatively easy to use. The fully compensated op amp is called a unity gain stable op amp. A decompensated op amp is designed to maximize the bandwidth and slew rate without any additional power consumption over the unity gain stable op amp. 11 www.national.com LMV793 LMV793 The LMV793 LMV793 requires a gain of ±10 to be stable. However, with an external compensation network (a simple RC network) these parts can be stable with gains of ±1 and maintain the higher slew rate. Looking at the Bode plots for the LMV793 LMV793 and its closest equivalent unity gain stable op amp, the LMV796 LMV796, one can clearly see the increased bandwidth of the LMV793 LMV793. Both plots are taken with a parallel combination of 20 pF and 10 k for the output load. Application Information LMV793 LMV793 20216325 FIGURE 4. LMV793 LMV793 with Lead-Lag Compensation for Inverting Configuration 20216324 To cover how to calculate the compensation network values it is necessary to introduce the term called the feedback factor or F. The feedback factor F is the feedback voltage VA-VB across the op amp input terminals relative to the op amp output voltage VOUT. FIGURE 3. Open Loop Gain for Unity-Gain Stable Op Amp and Decompensated Op Amp Having a higher frequency for the dominate pole will result in: 1. The DC open-loop gain (AVOL) extending to a higher frequency. 2. A wider closed loop bandwidth. 3. Better slew rate due to reduced compensation capacitance within the op amp. The second open loop pole (f2) for the LMV793 LMV793 occurs at 45 MHz. The unity gain (fu') occurs after the second pole at 51 MHz. An ideal two pole system would give a phase margin of 45° at the location of the second pole. The LMV793 LMV793 has parasitic poles close to the second pole, giving a phase margin closer to 0°. Therefore it is necessary to operate the LMV793 LMV793 at a closed loop gain of 10 or higher in order to assure stability, or to add external compensation as covered later in this datasheet. For the LMV796 LMV796, the gain bandwidth product occurs at 17 MHz. The curve is constant from fd to fu which occurs before the second pole. For the LMV793 LMV793, the GBW = 88 MHz and is constant between f1 and f2. The second pole at f2 occurs before AVOL = 1. Therefore fu' occurs at 51 MHz, well before the GBW frequency of 88 MHz. For decompensated op amps the unity gain frequency and the GBW are no longer equal. Gmin is the minimum gain for stability and for the LMV793 LMV793 this is a gain of 10 or 20 dB. From feedback theory the classic form of the feedback equation for op amps is: A is the open loop gain of the amplifier and the term AF is highly important in analyzing op amps. It is the loop gain. Normally AF >>1 and so the above equation reduces to: Deriving the equations for the lead-lag compensation is beyond the scope of this datasheet. The derivation is based on the feedback equations that have just been covered. The inverse of feedback factor for the circuit in Figure 4 is: Input Lead-Lag Compensation The recommended technique which allows the user to compensate the LMV793 LMV793 for stable operation at any gain is the lead-lag compensation. The compensation components added to the circuit allow the user to shape the feedback function to make sure there is sufficient phase margin when the loop gain is as low as 0 dB and still maintain the advantages over the unity gain op amp. Figure 4 shows the leadlag configuration. Only RC and C are added for the necessary compensation. (1) where 1/F's pole is located at (2) 1/F's zero is located at (3) (4) www.national.com 12 LMV793 LMV793 The circuit gain for Figure 4 at low frequencies is -RF/RIN, but F, the feedback factor is not equal to the circuit gain. The feedback factor is derived from feedback theory and is the same for both inverting and non-inverting configurations. Yes, the feedback factor at low frequencies is equal to the gain for the non-inverting configuration. (5) From this formula, we can see that · 1/F's zero is located at a lower frequency compared with 1/F's pole. · 1/F's value at low frequency is 1 + RF/RIN. · This method creates one additional pole and one additional zero. · This pole-zero pair will serve two purposes: - To raise the 1/F value at higher frequencies prior to its intercept with A, the open loop gain curve, in order to meet the Gmin = 10 requirement. For the LMV793 LMV793 some overcompensation will be necessary for good stability. - To achieve #1 above with no additional loop phase delay. Please note the constraint 1/F Gmin needs to be satisfied only in the vicinity where open loop gain A and 1/F intersects; 1/F can be shaped elsewhere as needed. The 1/F pole must occur before the intersection with the open loop gain A. In order to have adequate phase margin, it's desirable to follow these two rules: Rule 1 1/F and the open loop gain A should intersect at the frequency where there is a minimum of 45° of phase margin. When over-compensation is required the intersection point of A and 1/F is set at a frequency where the phase margin is above 45°, therefore increasing the stability of the circuit. Rule 2 1/F's pole should be set at least one decade below the intersection with the open loop gain A order to take the full 90° of phase lead brought by 1/F's pole which is F's zero. This ensures that the effect of the zero is fully neutralized when the 1/F and A plots intersect each other. 20216348 FIGURE 5. LMV793 LMV793 Simplified Bode Plot To obtain stable operation with gains under 10 V/V the open loop gain margin must be reduced at high frequencies to where there is a 45° phase margin when the gain margin of the circuit with the external compensation is 0 dB. The pole and zero in F, the feedback factor, controls the gain margin at the higher frequencies. The distance between F and AVOL is the gain margin; therefore the unity gain point (0 dB) is where F crosses the AVOL curve. For the example being used RIN = RF for a gain of -1. Therefore F = 6 dB at low frequencies. At the higher frequencies the minimum value for F is 18 dB for 45° phase margin. From Equation 5 we have the following relationship: Now set RF = RIN = R. With these values and solving for RC we have Rc = R/5.9. Note that the value of C does not affect the ratio between the resistors. Once the value of the resistors is set, then one must set the position of the pole in F. For this design a resistor value of 2 k has been selected for RF and RIN. Therefore the value for Rc is set at 330, the closest standard value for 2 k/5.9. Rewriting Equation 2 to solve for the minimum capacitor value gives the following equation: Calculating Lead-Lag Compensation for LMV793 LMV793 To cover the calculations for the lead-lag compensation the Bode plot show in Figure 1 has been simplified to easily show the key parameters used in these calculations. This is the same plot as Figure 1, but the AVOL and phase curves have been redrawn as smooth lines to easily show the concepts covered. C = 1/(2fpRc) The feedback factor curve, F, intersects the AVOL curve at about 12 MHz. Therefore the pole of F should not be any larger than 1.2 MHz. Using this value and Rc = 330 the minimum value for C is 390 pF. In Figure 6 one can see that there is too much overshoot, but the part is stable. Increasing C to 2.2 nF did not improve the ringing, as shown in Figure 7. 13 www.national.com LMV793 LMV793 20216310 20216303 FIGURE 9. RC = 240 and C = 2.2 nF, Gain = -1 FIGURE 6. First Try at Compensation, Gain = -1 To summarize, the following steps were taken to compensate the LMV793 LMV793 for a gain of -1: 1. Values for Rc and C were calculated from the Bodie plot to give an expected phase margin of 45°. The values are based on RIN = RF = 2 k. These calculations gave Rc = 330 and C = 390 pF. 2. To reduce the ringing C was increased to 2.2 nF which moved the pole of F, the feedback factor, farther away from the AVOL curve. 3. There was still too much ringing so 2 dB of overcompensation was added to F. This was done by decreasing RC to 240. The LMV796 LMV796 is the closest fully compensated part to the LMV793 LMV793. Using the same setup, but removing the compensation network, the result is shown in Figure 10 . 20216307 FIGURE 7. C Increased to 2.2 nF, Gain = -1 Some over-compensation appears to be needed for the desired overshoot characteristics. Instead of intersecting the AVOL curve at 18 dB, 2 dB of over-compensation will be used, and the AVOL curve will be intersected at 20 dB. Using Equation 5 for 20 dB, or 10 V/V, the closest standard value of RC is 240. The following two waveforms show the new resistor value with C = 390 pF and 2.2 nF. Figure 9 shows the final compensation and a very good response for the 1 MHz square wave. 20216321 FIGURE 10. LMV796 LMV796 Response For large signal response the rise and fall times are dominated by the slew rate of the op amps. Even though both parts are quite similar the LMV793 LMV793 will give rise and fall times about 2.5 times faster than the LMV796 LMV796 . This is possible because the LMV793 LMV793 is a decompensated op amp and by using a good external compensation technique the speed of the LMV793 LMV793 is preserved even though it is being used at a gain of -1. 20216308 FIGURE 8. RC = 240 and C = 390 pF, Gain = -1 www.national.com 14 20216384 FIGURE 13. LMV793 LMV793 with Lead-Lag Compensation for Non-Inverting Configuration Figure 13 is the result of using Equation 5 and additional experimentation in the lab. RP is not part of Equation 5, but it is necessary to introduce another pole at the input stage for good performance at gain = +1. Equation 5 is shown below with RIN = . Using 2 k for RF and solving for RC gives RC = 2000/6.9 = 290. The closest standard value for RC is 300. After some tuning in the lab RC = 330 and RP = 1.5 k. RP together with the input capacitance at the non-inverting pin inserts another pole into the compensation for the LMV793 LMV793. Adding this pole and slightly reducing the compensation for 1/F (using a slightly higher resistor value for RC) gives the optimum response for a gain of +1. Figure 14 shows the response of the circuit shown in Figure 13. Figure 14 shows the response of the LMV796 LMV796 in the buffer configuration with no compensation and RP = RF = 0. 20216382 FIGURE 11. RC = 240 and C = 2.2 nF, Gain = +2 20216383 FIGURE 12. LMV796 LMV796 Response Gain = +2 The response shown in Figure 11 is close to the response shown in Figure 9. The part is actually slightly faster in the non-inverting configuration. Decreasing the value of RC to around 200 can decrease the negative overshoot but will have slightly longer rise and fall times. The other option is to add a small resistor in series with the input signal, this is covered below for the gain = +1 configuration. Figure 12 shows the performance of the LMV796 LMV796 with no compensation. Again the decomposition parts are almost 2.5 times faster than the fully compensated op amp. The most difficult op amp configuration to stabilize is the gain of +1. With proper compensation the LMV793 LMV793 can be used in 20216388 FIGURE 14. RC = 330 and C = 10 nF, Gain = +1 15 www.national.com LMV793 LMV793 this configuration and still maintain the higher speed over the fully compensated parts. Figure 13 below shows the gain = 1, or the buffer configuration, for these parts. Non-Inverting Compensation For the non-inverting amp the same theory applies for establishing the needed compensation. When setting the inverting configuration for a gain of -1, F has a value of 2. For the noninverting configuration both F and the actual gain are the same, making the non-inverting configuration more difficult to compensate. Using the same circuit as shown in Figure 4, but setting up the circuit for non-inverting operation (gain of +2) results in similar performance as the inverting configuration with the inputs set to half the amplitude to compensate for the additional gain. Figure 11 below shows the results. LMV793 LMV793 Using the decompensated op amp offers faster speed over the compensated equivalent part with no increase in power consumption. The above experiments were done with RF = 2 k. This value is high enough to be easily driven by the LMV793 LMV793, yet small enough to minimize the affects from the parasitic capacitors from both the PCB and the op amp. Note: When using the LMV793 LMV793 proper high frequency PCB layout must be followed. The GBW of these parts is 88 MHz, making the PCB layout significantly more critical than using the compensated counterparts which have a GBW of 17 MHz. 20216389 FIGURE 15. LMV796 LMV796 Response Gain = +1 www.national.com 16 LMV793 LMV793 Physical Dimensions inches (millimeters) unless otherwise noted 5-Pin SOT23 NS Package Number MF05A MF05A 8-Pin SOIC NS Package Number M08A 17 www.national.com LMV793 LMV793 88 MHz, Low Noise, 1.8V CMOS Input, Decompensated Operational Amplifier Notes THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. 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