LM8261M5X

LM8261 Single RRIO, High Output Current & Unlimited Cap Load Op Amp in SOT23-5 April 2000 LM8261 Single RRIO, High Output Current & Unlimited Cap Load Op Amp in SOT23-5 General Description The LM8261 is a Rail-to-Rail input and output Op Amp which can operate with a wide supply voltage range. This device has high output current drive, greater than Rail-to-Rail input common mode voltage range, unlimited capacitive load drive capability, and provides tested and guaranteed high speed and slew rate while requiring only 0.97mA supply current. It is specifically designed to handle the requirements of flat panel TFT panel VCOM driver applications as well as being suitable for other low power, and medium speed applications which require ease of use and enhanced performance over existing devices. Greater than Rail-to-Rail input common mode voltage range with 50dB of Common Mode Rejection, allows high side and low side sensing, among many applications, without having any concerns over exceeding the range and no compromise in accuracy. Exceptionally wide operating supply voltage range of 2.5V to 30V alleviates any concerns over functionality under extreme conditions and offers flexibility of use in multitude of applications. In addition, most device parameters are insensitive to power supply variations; this design enhancement is yet another step in simplifying its usage. The output stage has low distortion (0.05% THD+N) and can supply a respectable amount of current (15mA) with minimal headroom from either rail (300mV). The LM8261 is offered in the space saving SOT23-5 package. Features (VS = 5V, TA = 25˚C, Typical values unless specified). n GBWP 21MHz n Wide supply voltage range 2.5V to 30V n Slew rate 12V/µs n Supply current 0.97 mA n Cap load limit Unlimited n Output short circuit current +53mA/−75mA n +/−5% Settling time 400ns (500pF, 100mVPP step) n Input common mode voltage 0.3V beyond rails n Input voltage noise 15nV/ n Input current noise 1pA/ < 0.05% n THD+N Applications n n n n TFT-LCD flat panel VCOM driver A/D converter buffer High side/low side sensing Headphone amplifier Output Response with Heavy Capacitive Load DS101084-37 © 2000 National Semiconductor Corporation DS101084 www.national.com LM8261 Connection Diagram SOT23-5 DS101084-62 Top View Ordering Information Package 5-Pin SOT-23 Ordering Info LM8261M5 LM8261M5X Pkg Marking A45A Supplied AS 1K Units Tape and Reel 3K Units Tape and Reel NSC Drawing MA05B www.national.com 2 LM8261 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. ESD Tolerance VIN Differential Output Short Circuit Duration Supply Voltage (V+ - V−) Voltage at Input/Output pins Storage Temperature Range 2KV (Note 2) 200V(Note 9) +/−10V (Notes 3, 11) 32V V+ +0.8V, V− −0.8V −65˚C to +150˚C Junction Temperature (Note 4) Soldering Information: Infrared or Convection (20 sec.) Wave Soldering (10 sec.) +150˚C 235˚C 260˚C Operating Ratings Supply Voltage (V+ - V−) Junction Temperature Range(Note 4) SOT23-5 Package Thermal Resistance, θJA,(Note 4) 325˚C/W 2.5V to 30V −40˚C to +85˚C 2.7V Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = 2.7V, V− = 0V, VCM = 0.5V, VO = V+/2, and RL > 1MΩ to V−. Boldface limits apply at the temperature extremes. Symbol VOS TC VOS IB Parameter Input Offset Voltage Input Offset Average Drift Input Bias Current Condition VCM = 0.5V & VCM = 2.2V VCM = 0.5V & VCM = 2.2V (Note 12) VCM = 0.5V (Note 7) VCM = 2.2V (Note 7) IOS CMRR Input Offset Current Common Mode Rejection Ratio VCM = 0.5V & VCM = 2.2V VCM stepped from 0V to 1.0V VCM stepped from 1.7V to 2.7V VCM stepped from 0V to 2.7V +PSRR CMVR Positive Power Supply Rejection Ratio Input Common-Mode Voltage Range V+ = 2.7V to 5V CMRR > 50dB Typ (Note 5) +/−0.7 +/−2 −1.20 +0.49 20 100 100 70 104 −0.3 3.0 AVOL Large Signal Voltage Gain VO = 0.5 to 2.2V, RL = 10K to V− VO = 0.5 to 2.2V, RL = 2K to V− VO Output Swing High RL = 10K to V− RL = 2K to V− Output Swing Low ISC Output Short Circuit Current RL = 10K to V− Sourcing to V− VID = 200mV (Note 10) Sinking to V+ VID = −200mV (Note 10) IS SR Supply Current Slew Rate (Note 8) No load, VCM = 0.5V AV = +1,VI = 2VPP 78 73 2.59 2.53 90 48 65 0.95 9 58 50 78 74 −0.1 0.0 2.8 2.7 70 67 67 63 2.49 2.46 2.45 2.41 100 120 30 20 50 30 1.20 1.50 – Limit (Note 6) +/−5 +/−7 – −2.00 −2.70 +1.00 +1.60 250 400 76 60 Units mV max µV/C µA max nA max dB min dB min V max V min dB min dB min V min mV max mA min mA min mA max V/µs 3 www.national.com LM8261 2.7V Electrical Characteristics (Continued) Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = 2.7V, V− = 0V, VCM = 0.5V, VO = V+/2, and RL > 1MΩ to V−. Boldface limits apply at the temperature extremes. Symbol fu GBWP Phim en in fmax Parameter Unity Gain-Frequency Gain Bandwidth Product Phase Margin Input-Referred Voltage Noise Input-Referred Current Noise Full Power Bandwidth Condition VI = 10mV, RL = 2KΩ to V+/2 f = 50KHz VI = 10mV f = 2KHz, RS = 50Ω f = 2KHz ZL = (20pF || 10KΩ) to V+/2 Typ (Note 5) 10 21 50 15 1 1 – Limit (Note 6) – 15.5 14 – – Units MHz MHz min Deg nV/ pA/ MHz 5V Electrical Characteristics Unless otherwise specified, all limited guaranteed for TJ = 25˚C, V+ = 5V, V− = 0V, VCM = 1V, VO = V+/2, and RL > 1MΩ to V−. Boldface limits apply at the temperature extremes. Symbol VOS TC VOS IB Parameter Input Offset Voltage Input Offset Average Drift Input Bias Current Condition VCM = 1V & VCM = 4.5V VCM = 1V & VCM = 4.5V (Note 12) VCM = 1V (Note 7) VCM = 4.5V (Note 7) IOS CMRR Input Offset Current Common Mode Rejection Ratio VCM = 1V & VCM = 4.5V VCM stepped from 0V to 3.3V VCM stepped from 4V to 5V VCM stepped from 0V to 5V +PSRR CMVR Positive Power Supply Rejection Ratio Input Common-Mode Voltage Range V+ = 2.7V to 5V, VCM = 0.5V CMRR > 50dB Typ (Note 5) +/−0.7 +/−2 −1.18 +0.49 20 110 100 80 104 −0.3 5.3 AVOL Large Signal Voltage Gain VO = 0.5 to 4.5V, RL = 10K to V− VO = 0.5 to 4.5V, RL = 2K to V− VO Output Swing High RL = 10K to V− RL = 2K to V− Output Swing Low ISC Output Short Circuit Current RL = 10K to V− Sourcing to V− VID = 200mV (Note 10) Sinking to V+ VID = −200mV (Note 10) 84 80 4.87 4.81 86 53 75 Limit (Note 6) +/−5 +/− 7 – −2.00 −2.70 +1.00 +1.60 250 400 84 72 – 64 61 78 74 −0.1 0.0 5.1 5.0 74 70 70 66 4.75 4.72 4.70 4.66 125 135 35 20 60 50 Units mV max µV/˚C µA max nA max dB min dB min V max V min dB min V min mV max mA min www.national.com 4 LM8261 5V Electrical Characteristics (Continued) Unless otherwise specified, all limited guaranteed for TJ = 25˚C, V+ = 5V, V− = 0V, VCM = 1V, VO = V+/2, and RL > 1MΩ to V−. Boldface limits apply at the temperature extremes. Symbol IS SR fu GBWP Phim en in fmax tS THD+N Parameter Supply Current Slew Rate (Note 8) Unity Gain Frequency Gain-Bandwidth Product Phase Margin Input-Referred Voltage Noise Input-Referred Current Noise Full Power Bandwidth Settling Time (+/−5%) Total Harmonic Distortion + Noise Condition No load, VCM = 1V AV = +1, VI = 5VPP VI = 10mV, RL = 2KΩ to V+/2 f = 50KHz VI = 10mV f = 2KHz, RS = 50Ω f = 2KHz ZL = (20pF || 10kΩ) to V+/2 100mVPP Step, 500pF load RL = 1KΩ to V+/2 f = 10KHz to AV = +2, 4VPP swing Typ (Note 5) 0.97 12 10.5 21 53 15 1 900 400 0.05 Limit (Note 6) 1.25 1.75 10 7 – 16 15 – – – – – – Units mA max V/µs min MHz MHz min Deg nV/ pA/ KHz ns % +/−15V Electrical Characteristics Unless otherwise specified, all limited guaranteed for TJ = 25˚C, V+ = 15V, V− = −15V, VCM = 0V, VO = 0V, and RL > 1MΩ to 0V. Boldface limits apply at the temperature extremes. Symbol VOS TC VOS IB Parameter Input Offset Voltage Input Offset Average Drift Input Bias Current Condition VCM = −14.5V & VCM = 14.5V VCM = −14.5V & VCM = 14.5V (Note 12) VCM = −14.5V (Note 7) VCM = 14.5V (Note 7) IOS CMRR Input Offset Current Common Mode Rejection Ratio VCM = −14.5V & VCM = 14.5V VCM stepped from −15V to 13V VCM stepped from 14V to 15V VCM stepped from −15V to 15V +PSRR −PSRR CMVR Positive Power Supply Rejection Ratio Negative Power Supply Rejection Ratio Input Common-Mode Voltage Range V+ = 12V to 15V V− = −12V to −15V CMRR > 50dB Typ (Note 5) +/−0.7 +/−2 −1.05 +0.49 30 100 100 88 100 100 −15.3 15.3 Limit (Note 6) +/−7 +/− 9 – −2.00 −2.80 +1.00 +1.50 275 550 84 80 – 74 72 70 66 70 66 −15.1 −15.0 15.1 15.0 Units mV max µV/˚C µA max nA max dB min dB min dB min V max V min 5 www.national.com LM8261 +/−15V Electrical Characteristics (Continued) Unless otherwise specified, all limited guaranteed for TJ = 25˚C, V+ = 15V, V− = −15V, VCM = 0V, VO = 0V, and RL > 1MΩ to 0V. Boldface limits apply at the temperature extremes. Symbol AVOL Parameter Large Signal Voltage Gain Condition VO = 0V to +/−13V, RL = 10KΩ VO = 0V to +/−13V, RL = 2KΩ VO Output Swing High RL = 10KΩ RL = 2KΩ Output Swing Low RL = 10KΩ RL = 2KΩ ISC Output Short Circuit Current Sourcing to ground VID = 200mV (Note 10) Sinking to ground VID = 200mV (Note 10) IS SR fu GBWP Phim en in fmax tS THD+N Supply Current Slew Rate (Note 8) Unity Gain Frequency Gain-Bandwidth Product Phase Margin Input-Referred Voltage Noise Input-Referred Current Noise Full Power Bandwidth Settling Time (+/−1%, AV = +1) Total Harmonic Distortion +Noise No load, VCM = 0V AV = +1, VI = 24VPP VI = 10mV, RL = 2KΩ f = 50KHz VI = 10mV f = 2KHz, RS = 50Ω f = 2KHz ZL = 20pF || 10KΩ Positive Step, 5VPP Negative Step, 5VPP RL = 1KΩ, f = 10KHz, AV = +2, 28VPP swing Typ (Note 5) 85 79 14.83 14.73 −14.91 −14.83 60 100 1.30 15 14 24 58 15 1 160 320 600 0.01 Limit (Note 6) 78 74 72 66 14.65 14.61 14.60 14.55 −14.75 −14.65 −14.65 −14.60 40 25 70 60 1.50 1.90 10 8 – 18 16 – – – – – – – Units dB min V min V max mA min mA max V/µs min MHz MHz min Deg nV/ pA/ KHz ns % Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Rating 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. Note 2: Human body model, 1.5kΩ in series with 100pF. Note 3: Applies to both single-supply and split-supply operation. Continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowed junction temperature of 150˚C. Note 4: 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. All numbers apply for packages soldered directly onto a PC board. Note 5: Typical Values represent the most likely parametric norm. Note 6: All limits are guaranteed by testing or statistical analysis. Note 7: Positive current corresponds to current flowing into the device. Note 8: Slew rate is the slower of the rising and falling slew rates. Connected as a Voltage Follower. Note 9: Machine Model, 0Ω is series with 200pF. Note 10: Short circuit test is a momentary test. See Note 11. Note 11: Output short circuit duration is infinite for VS ≤ 6V at room temperature and below. For VS > 6V, allowable short circuit duration is 1.5ms. Note 12: Offset voltage average drift determined by dividing the change in VOS at temperature extremes into the total temperature change. www.national.com 6 LM8261 Typical Performance Characteristics VOS vs. VCM for 3 Representative Units TA = 25˚C, Unless Otherwise Noted VOS vs. VCM for 3 Representative Units DS101084-30 DS101084-29 VOS vs. VCM for 3 Representative Units VOS vs. VS for 3 Representative Units DS101084-31 DS101084-34 VOS vs. VS for 3 Representative Units VOS vs. VS for 3 Representative Units DS101084-35 DS101084-33 7 www.national.com LM8261 Typical Performance Characteristics IB vs. VCM TA = 25˚C, Unless Otherwise Noted (Continued) IB vs. VS DS101084-24 DS101084-36 IS vs. VCM IS vs. VCM DS101084-27 DS101084-28 IS vs. VCM IS vs. VS (PNP side) DS101084-68 DS101084-25 www.national.com 8 LM8261 Typical Performance Characteristics IS vs. VS (NPN side) TA = 25˚C, Unless Otherwise Noted (Continued) Gain/Phase vs. Frequency DS101084-26 DS101084-18 Unity Gain Frequency vs. VS Phase Margin vs. VS DS101084-7 DS101084-8 Unity Gain Freq. and Phase Margin vs. VS Unity Gain Frequency vs. Load DS101084-4 DS101084-5 9 www.national.com LM8261 Typical Performance Characteristics Phase Margin vs. Load TA = 25˚C, Unless Otherwise Noted (Continued) Unity Gain Freq. and Phase Margin vs. CL DS101084-6 DS101084-9 CMRR vs. Frequency +PSRR vs. Frequency DS101084-14 DS101084-16 −PSRR vs. Frequency Output Voltage vs. Output Sourcing Current DS101084-17 DS101084-46 www.national.com 10 LM8261 Typical Performance Characteristics Output Voltage vs. Output Sourcing Current TA = 25˚C, Unless Otherwise Noted (Continued) Output Voltage vs. Output Sinking Current DS101084-44 DS101084-45 Max Output Swing vs. Load Max Output Swing vs. Frequency DS101084-10 DS101084-11 % Overshoot vs. Cap Load ± 5% Settling Time vs. Cap Load DS101084-48 DS101084-47 11 www.national.com LM8261 Typical Performance Characteristics +SR vs. Cap Load TA = 25˚C, Unless Otherwise Noted (Continued) −SR vs. Cap Load DS101084-51 DS101084-52 +SR vs. Cap Load −SR vs. Cap Load DS101084-49 DS101084-50 Settling Time vs. Error Voltage Settling Time vs. Error Voltage DS101084-43 DS101084-42 www.national.com 12 LM8261 Typical Performance Characteristics Input Noise Voltage/Current vs. Frequency TA = 25˚C, Unless Otherwise Noted (Continued) Input Noise Voltage for Various VCM DS101084-15 DS101084-13 Input Noise Current for Various VCM Input Noise Voltage vs. VCM DS101084-12 DS101084-55 Input Noise Current vs. VCM THD+N vs. Frequency DS101084-54 DS101084-23 13 www.national.com LM8261 Typical Performance Characteristics THD+N vs. Frequency TA = 25˚C, Unless Otherwise Noted (Continued) THD+N vs. Frequency DS101084-22 DS101084-21 THD+N vs. Amplitude THD+N vs. Amplitude DS101084-19 DS101084-20 Small Signal Step Response Large Signal Step Response DS101084-38 DS101084-40 www.national.com 14 LM8261 Application Notes: Block Diagram and Operational Description: A) Input Stage: As can be seen from the simplified schematic in Figure 1, the input stage consists of two distinct differential pairs (Q1-Q2 and Q3-Q4) in order to accommodate the full Rail-to-Rail input common mode voltage range. The voltage drop across R5, R6, R7, and R8 is kept to less than 200mV in order to allow the input to exceed the supply rails. Q13 acts as a switch to steer current away from Q3-Q4 and into Q1-Q2, as the input increases beyond 1.4V of V+. This in turn shifts the signal path from the bottom stage differential pair to the top one and causes a subsequent increase in the supply current. In transitioning from one stage to another, certain input stage parameters (Vos, Ib, Ios, en, and in) are determined based on which differential pair is ″on″ at the time. Input Bias current, Ib, will change in value and polarity as the input crosses the transition region. In addition, parameters such as PSRR and CMRR which involve the input offset voltage will also be effected by changes in VCM across the differential pair transition region. DS101084-66 FIGURE 2. Input Stage Current vs Differential Input Voltage B) Output Stage: The output stage Figure 1 is comprised of complementary NPN and PNP common-emitter stages to permit voltage swing to within a Vce(sat) of either supply rail. Q9 supplies the sourcing and Q10 supplies the sinking current load. Output current limiting is achieved by limiting the Vce of Q9 and Q10; using this approach to current limiting, alleviates the draw back to the conventional scheme which requires one Vbe reduction in output swing. The frequency compensation circuit includes Miller capacitors from collector to base of each output transistor (see Figure 1, Ccomp9 and Ccomp10). At light capacitive loads, the high frequency gain of the output transistors is high, and the Miller effect increases the effective value of the capacitors thereby stabilizing the Op Amp. Large capacitive loads greatly decrease the high frequency gain of the output transistors thus lowering the effective internal Miller capacitance - the internal pole frequency increases at the same time a low frequency pole is created at the Op Amp output due to the large load capacitor. In this fashion, the internal dominant pole compensation, which works by reducing the loop gain to less than 0dB when the phase shift around the feedback loop is more than 180˚C, varies with the amount of capacitive load and becomes less dominant when the load capacitor has increased enough. Hence the Op Amp is very stable even at high values of load capacitance resulting in the uncharacteristic feature of stability under all capacitive loads. Driving Capacitive Loads: The LM8261 is specifically designed to drive unlimited capacitive loads without oscillations (See Settling Time and Percent Overshoot vs. Cap Load plots in the typical performance characteristics section). In addition, the output current handling capability of the device allows for good slewing characteristics even with large capacitive loads (see Slew Rate vs. Cap Load plots). The combination of these features is ideal for applications such as TFT flat panel buffers, A/D converter input amplifiers, etc. However, as in most Op Amps, addition of a series isolation resistor between the Op Amp and the capacitive load improves the settling and overshoot performance. Output current drive is an important parameter when driving capacitive loads. This parameter will determine how fast the output voltage can change. Referring to the Slew Rate vs. Cap Load Plots (typical performance characteristics section), two distinct regions can be identified. Below about 10,000pF, the output Slew Rate is solely determined by the 15 www.national.com DS101084-67 FIGURE 1. Simplified schematic Diagram The input stage is protected with the combination of R9-R10 and D1, D2, D3, and D4 against differential input over-voltages. This fault condition could otherwise harm the differential pairs or cause offset voltage shift in case of prolonged over voltage. As shown in Figure 2, if this voltage reaches approximately +/−1.4V at 25˚C, the diodes turn on and current flow is limited by the internal series resistors (R9 and R10). The Absolute Maximum Rating of +/−10V differential on Vin still needs to be observed. With temperature variation, the point were the diodes turn on will change at the rate of 5mV/˚C. LM8261 Application Notes: (Continued) Op Amp’s compensation capacitor value and available current into that capacitor. Beyond 10nF, the Slew Rate is determined by the Op Amp’s available output current. Note that because of the lower output sourcing current compared to the sinking one, the Slew Rate limit under heavy capacitive loading is determined by the positive transitions. An estimate of positive and negative slew rates for loads larger than 100nF can be made by dividing the short circuit current value by the capacitor. For the LM8261, the available output current increases with the input overdrive. Referring to Figure 3 and Figure 4, Output Short Circuit Current vs. Input Overdrive, it can be seen that both sourcing and sinking short circuit current increase as input overdrive increases. In a closed loop amplifier configuration, during transient conditions while the fed back output has not quite caught up with the input, there will be an overdrive imposed on the input allowing more output current than would normally be available under steady state condition. Because of this feature, the Op Amp’s output stage quiescent current can be kept to a minimum, thereby reducing power consumption, while enabling the device to deliver large output current when the need arises (such as during transients). Figure 5 shows the output voltage, output current, and the resulting input overdrive with the device set for AV = +1 and the input tied to a 1Vpp step function driving a 47nF capacitor. As can be seen, during the output transition, the input overdrive reaches 1V peak and is more than enough to cause the output current to increase to its maximum value (see Figure 3 and Figure 4 plots). Note that because of the larger output sinking current compared to the sourcing one, the output negative transition is faster than the positive one. DS101084-39 FIGURE 5. Buffer Amplifier scope photo Estimating the output voltage swing: It is important to keep in mind that the steady state output current will be less than the current available when there is an input overdrive present. For steady state conditions, the Output Voltage vs. Output Current plot (Typical Performance Characteristics section) can be used to predict the output swing. Figure 6 and Figure 7 show this performance along with several load lines corresponding to loads tied between the output and ground. In each cases, the intersection of the device plot at the appropriate temperature with the load line would be the typical output swing possible for that load. For example, a 1KΩ load can accomadate an output swing to within 250mV of V− and to 330mV of V+ (Vs = +/−15V) corresponding to a typical 29.3Vpp unclipped swing. DS101084-57 FIGURE 3. Output Short Circuit Sourcing Current vs Input Overdrive DS101084-60 FIGURE 6. Output Sourcing Characteristics with Load Lines DS101084-56 FIGURE 4. Output Short Circuit Sinking Current vs Input Overdrive www.national.com 16 LM8261 Application Notes: (Continued) Output Short Circuit Current and Dissipation Issues: The LM8261 output stage is designed for maximum output current capability. Even though momentary output shorts to ground and either supply can be tolerated at all operating voltages, longer lasting short conditions can cause the junction temperature to rise beyond the absolute maximum rating of the device, especially at higher supply voltage conditions. Below supply voltage of 6V, output short circuit condition can be tolerated indefinitely. With the Op Amp tied to a load, the device power dissipation consists of the quiescent power due to the supply current flow into the device, in addition to power dissipation due to the load current. The load portion of the power itself could include an average value (due to a DC load current) and an AC component. DC load current would flow if there is an output voltage offset, or the output AC average current is non-zero, or if the Op Amp operates in a single supply application where the output is maintained somewhere in the range of linear operation. Therefore: Ptotal = PQ + PDC + PAC PQ = IS · VS PDC = IO · (Vr - Vo) PAC = See Table 1 below where: Is: Supply Current Vs: Total Supply Voltage (V+ - V−) Io: Average load current Vo: Average Output Voltage Vr: V+ for sourcing and V− for sinking current Op Amp Quiescent Power Dissipation DC Load Power AC Load Power DS101084-59 FIGURE 7. Output Sinking Characteristics with Load Lines TFT applications: Figure 8 below, shows a typical application where the LM8261 is used as a buffer amplifier for the Vcom signal employed in a TFT LCD flat panel: DS101084-61 Table 1 below shows the maximum AC component of the load power dissipated by the Op Amp for standard Sinusoidal, Triangular, and Square Waveforms: TABLE 1. Normalized AC Power Dissipated in the Output Stage for Standard Waveforms PAC (W.Ω/V2) Sinusoidal 50.7 x 10 −3 FIGURE 8. Vcom driver application schematic Figure 9 shows the time domain response of the amplifier when used as a Vcom buffer/driver with VREF at ground. In this application, the Op Amp loop will try and maintain its output voltage based on the voltage on its non-inverting input (VREF) despite the current injected into the TFT simulated load. As long as this load current is within the range tolerable by the LM8261 (45mA sourcing and 65mA sinking for +/−5V supplies), the output will settle to its final value within less than 2µs. Triangular 46.9 x 10 −3 2 Square 62.5 x 10−3 The table entries are normalized to Vs / RL. To figure out the AC load current component of power dissipation, simply multiply the table entry corresponding to the output waveform by the factor Vs2/ RL. For example, with ± 15V supplies, a 600Ω load, and triangular waveform power dissipation in the output stage is calculated as: PAC = (46.9 x 10−3) · [302/600]= 70.4mW DS101084-65 FIGURE 9. Vcom driver performance scope photo 17 www.national.com LM8261 Application Notes: Other Application Hints: (Continued) LM8261 Advantages: Compared to other Rail-to-Rail Input/Output devices, the LM8261 offers several advantages such as: The use of supply decoupling is mandatory in most applications. As with most relatively high speed/high output current Op Amps, best results are achieved when each supply line is decoupled with two capacitors; a small value ceramic capacitor (∼0.01µF) placed very close to the supply lead in addition to a large value Tantalum or Aluminum ( > 4.7µF). The large capacitor can be shared by more than one device if necessary. The small ceramic capacitor maintains low supply impedance at high frequencies while the large capacitor will act as the charge ″bucket″ for fast load current spikes at the Op Amp output. The combination of these capacitors will provide supply decoupling and will help keep the Op Amp oscillation free under any load. • • • • • Improved cross over distortion. Nearly constant supply current throughout the output voltage swing range and close to either rail. Consistent stability performance for all input/output voltage and current conditions. Nearly constant Unity gain frequency (fu) and Phase Margin (Phim) for all operating supplies and load conditions. No output phase reversal under input overload condition. www.national.com 18 LM8261 Single RRIO, High Output Current & Unlimited Cap Load Op Amp in SOT23-5 Physical Dimensions inches (millimeters) unless otherwise noted 5-Pin SOT23-5 NS Package Number MA05B 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. 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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