LM6172 Dual High Speed, Low Power, Low Distortion, Voltage Feedback Amplifiers General Description Features 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. (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 LM6172 Dual High Speed, Low Power, Low Distortion, Voltage Feedback Amplifiers May 1999 Ordering Information Package Temperature Range Industrial Military −40˚C to +85˚C −55˚C to +125˚C Transport Media NSC Drawing Rails N08E 8-Pin DIP LM6172IN 8-Pin CDIP LM6172AMJ-QML 5962-95604 Rails J08A 10-Pin Ceramic SOIC LM6172AMWG-QML 5962-95604 Trays WG10A 8-Pin LM6172IM Rails M08A LM6172IMX Tape and Reel Small Outline www.national.com 2 Absolute Maximum Ratings (Note 1) Maximum Junction Temperature (Note 4) 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 150˚C Operating Ratings(Note 1) 5.5V ≤ VS ≤ 36V Supply Voltage Junction Temperature Range LM6172I Thermal Resistance (θJA) N Package, 8-Pin Molded DIP M Package, 8-Pin Surface Mount 3 kV 300V 36V ± 10V −40˚C ≤ TJ ≤ +85˚C 95˚C/W 160˚C/W Continuous −65˚C to +150˚C ± 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 Parameter Conditions Typ (Note 5) LM6172I Limit Units (Note 5) VOS TC VOS Input Offset Voltage 0.4 Input Offset Voltage 3 mV 4 max 6 µV/˚C Average Drift IB IOS RIN Input Bias Current 1.2 Input Offset Current Input Resistance 0.02 Common Mode 40 Differential Mode 4.9 3 µA 4 max 2 µA 3 max MΩ Ω RO Open Loop Output Resistance CMRR Common Mode Rejection Ratio VCM = ± 10V 110 70 dB 65 min PSRR Power Supply Rejection Ratio VS = ± 15V to ± 5V 95 75 dB 70 min AV Large Signal Voltage 14 RL = 1 kΩ 86 Gain (Note 6) RL = 100Ω VO Output Swing RL = 1 kΩ 78 13.2 −13.1 RL = 100Ω 9 −8.5 Continuous Output Current Sourcing, RL = 100Ω 90 (Open Loop) (Note 7) Sinking, RL = 100Ω ISC IS −85 Output Short Circuit Sourcing 107 Current Sinking −105 Supply Current Both Amplifiers 3 4.6 80 dB 75 min 65 dB 60 min 12.5 V 12 min −12.5 V −12 max 6 V 5 min −6 V −5 max 60 mA 50 min −60 mA −50 max mA mA 8 mA www.national.com ± 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 Units (Note 5) 9 max ± 15V AC Electrical Characteristics Unless otherwise specified, TJ = 25˚C, V+ = +15V, V− = −15V, VCM = 0V, and RL = 1 kΩ LM6172I Symbol Parameter Conditions Typ Units (Note 5) SR AV = +2, VIN = 13 VPP AV = +2, VIN = 10 VPP Slew Rate 3000 Unity-Gain Bandwidth AV = +1 AV = +2 −3 dB Frequency Bandwidth Matching between Channels V/µs 2500 V/µs 100 MHz 160 MHz 62 MHz 2 MHz 40 Deg 65 ns φm Phase Margin ts Settling Time (0.1%) AD Differential Gain (Note 8) 0.28 % φD Differential Phase (Note 8) 0.6 Deg en Input-Referred AV = −1, VOUT = ± 5V, RL = 500Ω f = 1 kHz 12 f = 1 kHz 1 −110 dB −50 dB Third Harmonic f = 10 kHz f = 5 MHz f = 10 kHz −105 dB Distortion (Note 10) f = 5 MHz −50 dB Voltage Noise in Input-Referred Current Noise Second Harmonic Distortion (Note 10) ± 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 Parameter Conditions Typ (Note 5) LM6172I Limit Units (Note 5) VOS TC VOS Input Offset Voltage 0.1 Input Offset Voltage 3 mV 4 max 4 µV/˚C Average Drift IB IOS RIN Input Bias Current Input Offset Current Input Resistance RO Output Resistance CMRR Common Mode Rejection Ratio www.national.com 1.4 0.02 Common Mode 40 Differential Mode 4.9 VCM = ± 2.5V 105 2.5 µA 3.5 max 1.5 µA 2.2 max MΩ Ω 14 4 70 dB ± 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 Units (Note 5) 65 PSRR AV Power Supply Rejection Ratio Large Signal Voltage VS = ± 15V to ± 5V RL = 1 kΩ 95 82 Gain (Note 6) RL = 100Ω VO 78 RL = 1 kΩ Output Swing 3.4 −3.3 RL = 100Ω 2.9 −2.7 Continuous Output Current Sourcing, RL = 100Ω 29 (Open Loop) (Note 7) Sinking, RL = 100Ω ISC IS −27 min 75 dB 70 min 70 dB 65 min 65 dB 60 min 3.1 V 3 min −3.1 V −3 max 2.5 V 2.4 min −2.4 V −2.3 max 25 mA 24 min −24 mA −23 max Output Short Circuit Sourcing 93 mA Current Sinking −72 mA Supply Current Both Amplifiers 4.4 6 mA 7 max ± 5V AC Electrical Characteristics Unless otherwise specified, TJ = 25˚C, V+ = +5V, V− = −5V, VCM = 0V, and RL = 1 kΩ. Symbol SR Parameter Slew Rate Conditions AV = +2, VIN = 3.5 VPP Unity-Gain Bandwidth −3 dB Frequency LM61722 Typ (Note 5) Units 750 V/µs 70 MHz AV = +1 AV = +2 130 MHz 45 MHz 57 Deg AV = −1, VOUT = ± 1V, RL = 500Ω 72 ns φm Phase Margin ts Settling Time (0.1%) AD Differential Gain (Note 8) 0.4 % φD Differential Phase (Note 8) 0.7 Deg en Input-Referred f = 1 kHz 11 f = 1 kHz 1 f = 10 kHz f = 5 MHz f = 10 kHz −110 dB −48 dB −105 dB Voltage Noise in Input-Referred Current Noise Second Harmonic Distortion (Note 10) Third Harmonic 5 www.national.com ± 5V AC Electrical Characteristics (Continued) Unless otherwise specified, TJ = 25˚C, V+ = +5V, V− = −5V, VCM = 0V, and RL = 1 kΩ. Symbol Parameter Conditions LM61722 Typ (Note 5) Units −50 dB f = 5 MHz Distortion (Note 10) 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 Supply Current vs Temperature DS012581-14 Input Bias Current vs Temperature DS012581-15 Short Circuit Current vs Temperature (Sourcing) 6 DS012581-16 Short Circuit Current vs Temperature (Sinking) DS012581-18 DS012581-17 www.national.com Input Offset Voltage vs Temperature DS012581-35 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 PSRR vs Frequency DS012581-37 PSRR vs Frequency DS012581-20 Open-Loop Frequency Response 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 DS012581-38 DS012581-23 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 DS012581-39 Input Current Noise vs Frequency Input Voltage Noise vs Frequency DS012581-40 Input Current Noise vs Frequency DS012581-42 Slew Rate vs Input Voltage DS012581-41 Slew Rate vs Supply Voltage DS012581-43 DS012581-25 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 DS012581-3 www.national.com DS012581-4 8 Small Signal Pulse Response AV = +1, VS = ± 5V DS012581-5 Typical Performance Characteristics Large Signal Pulse Response AV = +2, VS = ± 15V unless otherwise noted, TA = 25˚C (Continued) Small Signal Pulse Response AV = +2, VS = ± 15V DS012581-6 Small Signal Pulse Response AV = +2, VS = ± 5V DS012581-7 Large Signal Pulse Response AV = −1, VS = ± 15V DS012581-9 Large Signal Pulse Response AV = −1, VS = ± 5V DS012581-10 Small Signal Pulse Response AV = −1, VS = ± 5V DS012581-12 Large Signal Pulse Response AV = +2, VS = ± 5V DS012581-8 Small Signal Pulse Response AV = −1, VS = ± 15V DS012581-11 Closed Loop Frequency Response vs Supply Voltage (AV = +1) 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) DS012581-29 Crosstalk Rejection vs Frequency DS012581-30 Maximum Power Dissipation vs Ambient Temperature DS012581-32 DS012581-31 www.national.com Harmonic Distortion vs Frequency (VS = ± 5V) 10 DS012581-34 ⁄ LM6172 Simplified Schematic 12 DS012581-55 Application Notes LM6172 Performance Discussion Reducing Settling Time 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. 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 board and can affect frequency performance. It is better to solder the amplifier directly into the PC board without using any socket. (Continued) 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 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. FIGURE 1. Isolation Resistor Used to Drive Capacitive Load Compensation for Input Capacitance 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 DS012581-51 FIGURE 2. The LM6172 Driving a 510 pF Load with a 30Ω Isolation Resistor 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 Power Supply Bypassing 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 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. 12 Power Supply Bypassing (Continued) DS012581-54 FIGURE 7. Improperly Terminated Signal DS012581-47 FIGURE 5. Power Supply Bypassing 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. 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 DS012581-53 FIGURE 6. Properly Terminated Signal 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 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: [email protected] www.national.com National Semiconductor Europe Fax: +49 (0) 1 80-530 85 86 Email: [email protected] 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. 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