LM6172IN

LM6172 Dual High Speed, Low Power, Low Distortion, Voltage Feedback Amplifiers May 1999 LM6172 Dual High Speed, Low Power, Low Distortion, Voltage Feedback Amplifiers General Description The LM6172 is a dual high speed voltage feedback amplifier. It is unity-gain stable and provides excellent DC and AC performance. With 100 MHz unity-gain bandwidth, 3000V/µs slew rate and 50 mA of output current per channel, the LM6172 offers high performance in dual amplifiers; yet it only consumes 2.3 mA of supply current each channel. The LM6172 operates on ± 15V power supply for systems requiring large voltage swings, such as ADSL, scanners and ultrasound equipment. It is also specified at ± 5V power supply for low voltage applications such as portable video systems. The LM6172 is built with National’s advanced VIP™ III (Vertically Integrated PNP) complementary bipolar process. See the LM6171 datasheet for a single amplifier with these same features. Features (Typical Unless Otherwise Noted) n Easy to Use Voltage Feedback Topology n High Slew Rate 3000V/µs n Wide Unity-Gain Bandwidth 100 MHz n Low Supply Current 2.3 mA/Channel n High Output Current 50 mA/channel n Specified for ± 15V and ± 5V Operation Applications n n n n n n n Scanner I-to-V Converters ADSL/HDSL Drivers Multimedia Broadcast Systems Video Amplifiers NTSC, PAL ® and SECAM Systems ADC/DAC Buffers Pulse Amplifiers and Peak Detectors LM6172 Driving Capacitive Load DS012581-44 DS012581-50 Connection Diagram 8-Pin DIP/SO DS012581-1 Top View VIP™ is a trademark of National Semiconductor Corporation. PAL ® is a registered trademark of and used under license from Advanced Micro Devices, Inc. © 1999 National Semiconductor Corporation DS012581 www.national.com Ordering Information Package Temperature Range Industrial −40˚C to +85˚C 8-Pin DIP 8-Pin CDIP 10-Pin Ceramic SOIC 8-Pin Small Outline LM6172IMX Tape and Reel LM6172IN LM6172AMJ-QML LM6172AMWG-QML LM6172IM 5962-95604 5962-95604 Military −55˚C to +125˚C Rails Rails Trays Rails N08E J08A WG10A M08A Transport Media NSC Drawing www.national.com 2 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 (Note 2) Human Body Model Machine Model Supply Voltage (V+ − V−) Differential Input Voltage (Note 9) Output Short Circuit to Ground (Note 3) Storage Temp. Range 3 kV 300V 36V ± 10V Continuous −65˚C to +150˚C Maximum Junction Temperature (Note 4) 150˚C Operating Ratings(Note 1) Supply Voltage Junction Temperature Range LM6172I Thermal Resistance (θJA) N Package, 8-Pin Molded DIP M Package, 8-Pin Surface Mount 5.5V ≤ VS ≤ 36V −40˚C ≤ TJ ≤ +85˚C 95˚C/W 160˚C/W ± 15V DC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C,V+ = +15V, V− = −15V, VCM = 0V, and RL = 1 kΩ. Boldface limits apply at the temperature extremes Symbol VOS TC VOS IB IOS RIN RO CMRR PSRR AV Parameter Input Offset Voltage Input Offset Voltage Average Drift Input Bias Current Input Offset Current Input Resistance Open Loop Output Resistance Common Mode Rejection Ratio Power Supply Rejection Ratio Large Signal Voltage Gain (Note 6) RL = 100Ω VO Output Swing RL = 1 kΩ 78 13.2 −13.1 RL = 100Ω 9 −8.5 Continuous Output Current (Open Loop) (Note 7) Sinking, RL = 100Ω ISC IS Output Short Circuit Current Supply Current Sourcing Sinking Both Amplifiers 3 Conditions Typ (Note 5) LM6172I Limit (Note 5) 3 4 Units mV max µV/˚C 3 4 2 3 µA max µA max MΩ Ω 70 65 75 70 80 75 65 60 12.5 12 −12.5 −12 6 5 −6 −5 60 50 −60 −50 dB min dB min dB min dB min V min V max V min V max mA min mA max mA mA 8 mA www.national.com 0.4 6 1.2 0.02 Common Mode Differential Mode VCM = ± 10V VS = ± 15V to ± 5V RL = 1 kΩ 40 4.9 14 110 95 86 Sourcing, RL = 100Ω 90 −85 107 −105 4.6 ± 15V DC Electrical Characteristics (Continued) Unless otherwise specified, all limits guaranteed for TJ = 25˚C,V+ = +15V, V− = −15V, VCM = 0V, and RL = 1 kΩ. Boldface limits apply at the temperature extremes Symbol Parameter Conditions Typ (Note 5) LM6172I Limit (Note 5) 9 max Units ± 15V AC Electrical Characteristics Unless otherwise specified, TJ = 25˚C, V+ = +15V, V− = −15V, VCM = 0V, and RL = 1 kΩ LM6172I Symbol SR Slew Rate Unity-Gain Bandwidth −3 dB Frequency Bandwidth Matching between Channels φm ts AD φD en Phase Margin Settling Time (0.1%) Differential Gain (Note 8) Differential Phase (Note 8) Input-Referred Voltage Noise in Input-Referred Current Noise Second Harmonic Distortion (Note 10) Third Harmonic Distortion (Note 10) f = 10 kHz f = 5 MHz f = 10 kHz f = 5 MHz −110 −50 −105 −50 dB dB dB dB f = 1 kHz 1 f = 1 kHz AV = −1, VOUT = ± 5V, RL = 500Ω AV = +1 AV = +2 Parameter Conditions AV = +2, VIN = 13 VPP AV = +2, VIN = 10 VPP Typ (Note 5) 3000 2500 100 160 62 2 40 65 0.28 0.6 12 V/µs V/µs MHz MHz MHz MHz Deg ns % Deg Units ± 5V DC Electrical Characteristics Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = +5V, V− = −5V, VCM = 0V, and RL = 1 kΩ. Boldface limits apply at the temperature extremes Symbol VOS TC VOS IB IOS RIN RO CMRR www.national.com Parameter Input Offset Voltage Input Offset Voltage Average Drift Input Bias Current Input Offset Current Input Resistance Output Resistance Common Mode Rejection Ratio Conditions Typ (Note 5) LM6172I Limit (Note 5) 3 4 Units mV max µV/˚C 2.5 3.5 1.5 2.2 µA max µA max MΩ Ω 70 dB 0.1 4 1.4 0.02 Common Mode Differential Mode VCM = ± 2.5V 4 40 4.9 14 105 ± 5V DC Electrical Characteristics (Continued) Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = +5V, V− = −5V, VCM = 0V, and RL = 1 kΩ. Boldface limits apply at the temperature extremes Symbol Parameter Conditions Typ (Note 5) LM6172I Limit (Note 5) 65 PSRR AV Power Supply Rejection Ratio Large Signal Voltage Gain (Note 6) RL = 100Ω VO Output Swing RL = 1 kΩ 78 3.4 −3.3 RL = 100Ω 2.9 −2.7 Continuous Output Current (Open Loop) (Note 7) Sinking, RL = 100Ω ISC IS Output Short Circuit Current Supply Current Sourcing Sinking Both Amplifiers −27 93 −72 4.4 6 7 Sourcing, RL = 100Ω 29 VS = ± 15V to ± 5V RL = 1 kΩ 95 82 75 70 70 65 65 60 3.1 3 −3.1 −3 2.5 2.4 −2.4 −2.3 25 24 −24 −23 min dB min dB min dB min V min V max V min V max mA min mA max mA mA mA max Units ± 5V AC Electrical Characteristics Unless otherwise specified, TJ = 25˚C, V+ = +5V, V− = −5V, VCM = 0V, and RL = 1 kΩ. Symbol SR Slew Rate Unity-Gain Bandwidth −3 dB Frequency φm ts AD φD en in Phase Margin Settling Time (0.1%) Differential Gain (Note 8) Differential Phase (Note 8) Input-Referred Voltage Noise Input-Referred Current Noise Second Harmonic Distortion (Note 10) Third Harmonic f = 10 kHz f = 5 MHz f = 10 kHz −110 −48 −105 dB dB dB f = 1 kHz 1 f = 1 kHz AV = −1, VOUT = ± 1V, RL = 500Ω AV = +1 AV = +2 Parameter Conditions AV = +2, VIN = 3.5 VPP LM61722 Typ (Note 5) 750 70 130 45 57 72 0.4 0.7 11 Units V/µs MHz MHz MHz Deg ns % Deg 5 www.national.com ± 5V AC Electrical Characteristics Symbol Parameter Distortion (Note 10) (Continued) Unless otherwise specified, TJ = 25˚C, V+ = +5V, V− = −5V, VCM = 0V, and RL = 1 kΩ. Conditions f = 5 MHz LM61722 Typ (Note 5) −50 Units dB 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. Note 2: Human body model, 1.5 kΩ in series with 100 pF. Machine Model, 200Ω in series with 100 pF. Note 3: Continuous short circuit operation 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 into 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: Large signal voltage gain is the total output swing divided by the input signal required to produce that swing. For VS = ± 15V, VOUT = ± 5V. For VS = ± 5V, VOUT = ± 1V. Note 8: The open loop output current is the output swing with the 100Ω load resistor divided by that resistor. Note 9: Differential gain and phase are measured with AV = +2, VIN = 1 VPP at 3.58 MHz and both input and output 75Ω terminated. Note 10: Differential input voltage is applied at VS = ± 15V. Note 11: Harmonics are measured with AV = +2, VIN = 1 VPP and RL = 100Ω. Typical Performance Characteristics Supply Voltage vs Supply Current unless otherwise noted, TA = 25˚C Input Offset Voltage vs Temperature Supply Current vs Temperature DS012581-14 DS012581-15 DS012581-16 Input Bias Current vs Temperature Short Circuit Current vs Temperature (Sourcing) Short Circuit Current vs Temperature (Sinking) DS012581-17 DS012581-18 DS012581-35 www.national.com 6 Typical Performance Characteristics Output Voltage vs Output Current (VS = ± 15V) unless otherwise noted, TA = 25˚C (Continued) Output Voltage vs Output Current (VS = ± 5V) CMRR vs Frequency DS012581-19 DS012581-36 DS012581-37 PSRR vs Frequency PSRR vs Frequency Open-Loop Frequency Response DS012581-20 DS012581-33 DS012581-21 Open-Loop Frequency Response Gain-Bandwidth Product vs Supply Voltage at Different Temperature Large Signal Voltage Gain vs Load DS012581-22 DS012581-23 DS012581-38 7 www.national.com Typical Performance Characteristics Large Signal Voltage Gain vs Load unless otherwise noted, TA = 25˚C (Continued) Input Voltage Noise vs Frequency Input Voltage Noise vs Frequency DS012581-39 DS012581-40 DS012581-41 Input Current Noise vs Frequency Input Current Noise vs Frequency Slew Rate vs Supply Voltage DS012581-42 DS012581-43 DS012581-25 Slew Rate vs Input Voltage Large Signal Pulse Response AV = +1, VS = ± 15V DS012581-2 DS012581-26 Small Signal Pulse Response AV = +1, VS = ± 15V Large Signal Pulse Response AV = +1, VS = ± 5V Small Signal Pulse Response AV = +1, VS = ± 5V DS012581-3 DS012581-4 DS012581-5 www.national.com 8 Typical Performance Characteristics Large Signal Pulse Response AV = +2, VS = ± 15V unless otherwise noted, TA = 25˚C (Continued) Large Signal Pulse Response AV = +2, VS = ± 5V Small Signal Pulse Response AV = +2, VS = ± 15V DS012581-6 DS012581-7 DS012581-8 Small Signal Pulse Response AV = +2, VS = ± 5V Large Signal Pulse Response AV = −1, VS = ± 15V Small Signal Pulse Response AV = −1, VS = ± 15V DS012581-9 DS012581-10 DS012581-11 Large Signal Pulse Response AV = −1, VS = ± 5V Small Signal Pulse Response AV = −1, VS = ± 5V Closed Loop Frequency Response vs Supply Voltage (AV = +1) DS012581-12 DS012581-13 DS012581-28 9 www.national.com Typical Performance Characteristics Closed Loop Frequency Response vs Supply Voltage (AV = +2) unless otherwise noted, TA = 25˚C (Continued) Harmonic Distortion vs Frequency (VS = ± 15V) Harmonic Distortion vs Frequency (VS = ± 5V) DS012581-29 DS012581-30 DS012581-34 Crosstalk Rejection vs Frequency Maximum Power Dissipation vs Ambient Temperature DS012581-31 DS012581-32 www.national.com 10 12 ⁄ LM6172 Simplified Schematic DS012581-55 Application Notes LM6172 Performance Discussion The LM6172 is a dual high-speed, low power, voltage feedback amplifier. It is unity-gain stable and offers outstanding performance with only 2.3 mA of supply current per channel. The combination of 100 MHz unity-gain bandwidth, 3000V/µs slew rate, 50 mA per channel output current and other attractive features makes it easy to implement the LM6172 in various applications. Quiescent power of the LM6172 is 138 mW operating at ± 15V supply and 46 mW at ± 5V supply. Reducing Settling Time The LM6172 has a very fast slew rate that causes overshoot and undershoot. To reduce settling time on LM6172, a 1 kΩ resistor can be placed in series with the input signal to decrease slew rate. A feedback capacitor can also be used to reduce overshoot and undershoot. This feedback capacitor serves as a zero to increase the stability of the amplifier circuit. A 2 pF feedback capacitor is recommended for initial evaluation. When the LM6172 is configured as a buffer, a feedback resistor of 1 kΩ must be added in parallel to the feedback capacitor. Another possible source of overshoot and undershoot comes from capacitive load at the output. Please see the section “Driving Capacitive Loads” for more detail. LM6172 Circuit Operation The class AB input stage in LM6172 is fully symmetrical and has a similar slewing characteristic to the current feedback amplifiers. In the LM6172 Simplified Schematic, Q1 through Q4 form the equivalent of the current feedback input buffer, RE the equivalent of the feedback resistor, and stage A buffers the inverting input. The triple-buffered output stage isolates the gain stage from the load to provide low output impedance. Driving Capacitive Loads Amplifiers driving capacitive loads can oscillate or have ringing at the output. To eliminate oscillation or reduce ringing, an isolation resistor can be placed as shown in Figure 1. The combination of the isolation resistor and the load capacitor forms a pole to increase stability by adding more phase margin to the overall system. The desired performance depends on the value of the isolation resistor; the bigger the isolation resistor, the more damped (slow) the pulse response becomes. For LM6172, a 50Ω isolation resistor is recommended for initial evaluation. LM6172 Slew Rate Characteristic The slew rate of LM6172 is determined by the current available to charge and discharge an internal high impedance node capacitor. This current is the differential input voltage divided by the total degeneration resistor RE. Therefore, the slew rate is proportional to the input voltage level, and the higher slew rates are achievable in the lower gain configurations. When a very fast large signal pulse is applied to the input of an amplifier, some overshoot or undershoot occurs. By placing an external series resistor such as 1 kΩ to the input of LM6172, the slew rate is reduced to help lower the overshoot, which reduces settling time. 11 www.national.com Driving Capacitive Loads (Continued) board and can affect frequency performance. It is better to solder the amplifier directly into the PC board without using any socket. USING PROBES Active (FET) probes are ideal for taking high frequency measurements because they have wide bandwidth, high input impedance and low input capacitance. However, the probe ground leads provide a long ground loop that will produce errors in measurement. Instead, the probes can be grounded directly by removing the ground leads and probe jackets and using scope probe jacks. DS012581-45 FIGURE 1. Isolation Resistor Used to Drive Capacitive Load COMPONENTS SELECTION AND FEEDBACK RESISTOR It is important in high speed applications to keep all component leads short because wires are inductive at high frequency. For discrete components, choose carbon composition-type resistors and mica-type capacitors. Surface mount components are preferred over discrete components for minimum inductive effect. Large values of feedback resistors can couple with parasitic capacitance and cause undesirable effects such as ringing or oscillation in high speed amplifiers. For LM6172, a feedback resistor less than 1 kΩ gives optimal performance. Compensation for Input Capacitance DS012581-51 FIGURE 2. The LM6172 Driving a 510 pF Load with a 30Ω Isolation Resistor The combination of an amplifier’s input capacitance with the gain setting resistors adds a pole that can cause peaking or oscillation. To solve this problem, a feedback capacitor with a value CF > (RG x CIN)/RF can be used to cancel that pole. For LM6172, a feedback capacitor of 2 pF is recommended. Figure 4 illustrates the compensation circuit. DS012581-52 FIGURE 3. The LM6172 Driving a 220 pF Load with a 50Ω Isolation Resistor DS012581-46 FIGURE 4. Compensating for Input Capacitance Layout Consideration PRINTED CIRCUIT BOARDS AND HIGH SPEED OP AMPS There are many things to consider when designing PC boards for high speed op amps. Without proper caution, it is very easy to have excessive ringing, oscillation and other degraded AC performance in high speed circuits. As a rule, the signal traces should be short and wide to provide low inductance and low impedance paths. Any unused board space needs to be grounded to reduce stray signal pickup. Critical components should also be grounded at a common point to eliminate voltage drop. Sockets add capacitance to the www.national.com 12 Power Supply Bypassing Bypassing the power supply is necessary to maintain low power supply impedance across frequency. Both positive and negative power supplies should be bypassed individually by placing 0.01 µF ceramic capacitors directly to power supply pins and 2.2 µF tantalum capacitors close to the power supply pins. Power Supply Bypassing (Continued) DS012581-54 DS012581-47 FIGURE 7. Improperly Terminated Signal To minimize reflection, coaxial cable with matching characteristic impedance to the signal source should be used. The other end of the cable should be terminated with the same value terminator or resistor. For the commonly used cables, RG59 has 75Ω characteristic impedance, and RG58 has 50Ω characteristic impedance. FIGURE 5. Power Supply Bypassing Termination In high frequency applications, reflections occur if signals are not properly terminated. Figure 6 shows a properly terminated signal while Figure 7 shows an improperly terminated signal. Power Dissipation The maximum power allowed to dissipate in a device is defined as: PD = (TJ(max) − TA)/θJA Where PD is the power dissipation in a device TJ(max) is the maximum junction temperature TA is the ambient temperature θJA is the thermal resistance of a particular package For example, for the LM6172 in a SO-8 package, the maximum power dissipation at 25˚C ambient temperature is 780 mW. Thermal resistance, θJA, depends on parameters such as die size, package size and package material. The smaller the die size and package, the higher θJA becomes. The 8-pin DIP package has a lower thermal resistance (95˚C/W) than that of 8-pin SO (160˚C/W). Therefore, for higher dissipation capability, use an 8-pin DIP package. The total power dissipated in a device can be calculated as: PD = PQ + PL PQ is the quiescent power dissipated in a device with no load connected at the output. PL is the power dissipated in the device with a load connected at the output; it is not the power dissipated by the load. Furthermore, PQ: = supply current x total supply voltage with no load output current x (voltage difference between supPL: = ply voltage and output voltage of the same supply) For example, the total power dissipated by the LM6172 with VS = ± 15V and both channels swinging output voltage of 10V into 1 kΩ is PD: = PQ + PL := 2[(2.3 mA)(30V)] + 2[(10 mA)(15V − 10V)] := 138 mW + 100 mW := 238 mW DS012581-53 FIGURE 6. Properly Terminated Signal 13 www.national.com Application Circuits I-to-V Converters DS012581-48 Differential Line Driver DS012581-49 www.national.com 14 Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead Ceramic Dual-In-Line Package Order Number LM6172AMJ-QML or 5962-9560401QPA NS Package Number J08A 8-Lead (0.150" Wide) Molded Small Outline Package, JEDEC Order Number LM6172IM or LM6172IMX NS Package Number M08A 15 www.national.com LM6172 Dual High Speed, Low Power, Low Distortion, Voltage Feedback Amplifiers Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 8-Lead (0.300" Wide) Molded Dual-In-Line Package Order Number LM6172IN NS Package Number N08E 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. National Semiconductor Corporation Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com www.national.com National Semiconductor Europe Fax: +49 (0) 1 80-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 1 80-530 85 85 English Tel: +49 (0) 1 80-532 78 32 Français Tel: +49 (0) 1 80-532 93 58 Italiano Tel: +49 (0) 1 80-534 16 80 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: sea.support@nsc.com National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507 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.