LM6182IN

LM6182 Dual 100 mA Output, 100 MHz Current Feedback Amplifier April 1994 LM6182 Dual 100 mA Output, 100 MHz Current Feedback Amplifier General Description The LM6182 dual current feedback amplifier offers an unparalleled combination of bandwidth, slew-rate, and output current. Each amplifier can directly drive a 2V signal into a 50Ω or 75Ω back-terminated coax cable system over the full industrial temperature range. This represents a radical enhancement in output drive capability for a dual 8-pin high-speed amplifier making it ideal for video applications. Built on National’s advanced high-speed VIP II™ (Vertically Integrated PNP) process, the LM6182 employs current-feedback providing bandwidth that does not vary dramatically with gain; 100 MHz at Av = −1, 60 MHz at Av = −10. With a slew rate of 2000 V/µsec, 2nd harmonic distortion of −50 dBc at 10 MHz and settling time of 50 ns (0.1%), the two independent amplifiers of the LM6182 offer performance that is ideal for data acquisition, high-speed ATE, and precision pulse amplifier applications. See the LM6181 data sheet for a single amplifier with these same features. Features (Typical unless otherwise noted) n Slew Rate: 2000 V/µs n Closed Loop Bandwidth: 100 MHz n Settling Time (0.1%): 50 ns n Low Differential Gain and Phase Error: 0.05%, 0.04˚ RL = 150Ω n Low Offset Voltage: 2 mV n High Output Drive: ± 10V into 150Ω n Characterized for Supply Ranges: ± 5V and ± 15V n Improved Performance over OP260 and LT1229 Applications n n n n n Coax Cable Driver Professional Studio Video Equipment Flash ADC Buffer PC and Workstation Video Boards Facsimile and Imaging Systems Typical Application DS011926-1 DS011926-2 VIP II™ is a trademark of National Semiconductor Corporation. © 1999 National Semiconductor Corporation DS011926 www.national.com Connection Diagrams Dual-In-Line Package (J) Small Outline Package (M) DS011926-51 Order Number LM6182AMJ/883 See NS Package Number J14A DS011926-4 *Heat Sinking Pins (Note 3) Order Number LM6182IM or LM6182AIM See NS Package Number M16A Dual-In-Line Package (N) DS011926-3 Order Number LM6182IN, LM6182AIN or LM6182AMN See NS Package Number N08E 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. Supply Voltage Differential Input Voltage Input Voltage Inverting Input Current Output Short Circuit ± 18V ± 6V ± Supply Voltage 15 mA (Note 4) Soldering Information Dual-In-Line Package (N) Soldering (10s) Small Outline Package (M) Vapor Phase (60s) Infrared (15s) Storage Temperature Range Junction Temperature ESD Rating (Note 2) 260˚C 215˚C 220˚C −65˚C ≤ TJ ≤ +150˚C 150˚C ± 2000V Operating Ratings Supply Voltage Range 7V to 32V Junction Temperature Range (Note 3) LM6182AM −55˚C ≤ TJ ≤ +125˚C LM6182AI, LM6182I −40˚C ≤ TJ ≤ +85˚C ± 15V DC Electrical Characteristics The following specifications apply for supply voltage = ± 15V, Vcm = VO = 0V, Rf = 820Ω, and RL = 1 kΩ unless otherwise noted. Boldface limits apply at the temperature extremes; all other limits TJ = 25˚C. Symbol Parameter Conditions Typical (Note 5) LM6182AM LM6182AI Limit (Note 6) VOS TCVOS IB Input Offset Voltage Input Offset Voltage Drift Inverting Input Bias Current Non-Inverting Input Bias Current TCIB IB PSR Inverting Input Bias Current Drift Non-Inverting Input Bias Current Drift Inverting Input Bias Current Power Supply Rejection Non-Inverting Input Bias Current Power Supply Rejection IB CMR Inverting Input Bias Current Common Mode Rejection Non-Inverting Input Bias Current Common Mode Rejection CMRR PSRR RO RIN VO Common Mode Rejection Ratio Power Supply Rejection Ratio Output Resistance Non-Inverting Input Resistance Output Voltage Swing RL = 1 kΩ RL = 150Ω ISC Output Short Circuit Current −10V ≤ VCM ≤ +10V 60 80 0.2 10 12 11 100 11 10 9.5 5.6 70 37.5 11 10 9.5 6.0 70 40 11 10 9.5 6.0 70 40 mA min −10V ≤ VCM ≤ +10V 0.1 −10V ≤ VCM ≤ +10V 0.15 2.0 5.0 2.0 0.75 30 10 5.0 12.0 2.0 4.0 5.0 12.0 2.0 4.0 10.0 17.0 3.0 5.0 nA/˚C 0.5 3.0 0.5 1.5 0.5 1.0 0.5 1.0 50 47 70 67 AV = −1 f = 300 kHz 0.5 3.0 0.5 1.5 0.5 1.0 0.5 1.0 50 47 70 67 0.75 4.5 0.5 3.0 0.75 1.5 0.5 1.5 50 47 70 65 dB min dB min Ω MΩ V min µA/V max 3.0 4.0 Limit (Note 6) 3.0 3.5 LM6182I Limit (Note 6) 5.0 5.5 mV max µV/˚C µA max Units ± 4.5V ≤ VS ≤ ± 16V ± 4.5V ≤ VS ≤ ± 16V 0.1 0.05 ± 4.5V ≤ VS ≤ ± 16V 3 www.national.com ± 15V DC Electrical Characteristics Symbol Parameter (Continued) The following specifications apply for supply voltage = ± 15V, Vcm = VO = 0V, Rf = 820Ω, and RL = 1 kΩ unless otherwise noted. Boldface limits apply at the temperature extremes; all other limits TJ = 25˚C. Conditions Typical (Note 5) LM6182AM LM6182AI Limit (Note 6) ZT Transimpedance RL = 1 kΩ RL = 150Ω IS VCM Supply Current Input Common Mode Voltage Range No Load, VIN = 0V Both Amplifiers V+−1.7V V−+1.7V 1.8 1.4 15 1.0 0.4 0.8 0.3 20 22 Limit (Note 6) 1.0 0.5 0.8 0.35 20 22 LM6182I Limit (Note 6) 0.8 0.4 0.7 0.3 20 22 mA max V MΩ min Units ± 15V AC Electrical Characteristics The following specifications apply for supply voltage = ± 15V, Vcm = VO = 0V, Rf = 820Ω, and RL = 1 kΩ unless otherwise noted. Boldface limits apply at the temperature extremes; all other limits TJ = 25˚C. Symbol Parameter Conditions Typical (Note 5) LM6182AM LM6182AI Limit (Note 6) Xt BW Crosstalk Rejection Closed Loop Bandwidth −3 dB (Note 7) AV = +2 AV = +10 AV = −1 AV = −10 Closed Loop Bandwidth 0.1 dB Flat, RSOURCE = 200Ω PBW SR Power Bandwidth Slew Rate AV = +2, RL = 150Ω AV = −1, VO = 5 VPP Overdriven AV = −1, VO = ± 10V RL = 150Ω, (Note 8) AV = −1, VO = ± 5V RL = 150Ω VO = 1 VPP VO = 1 VPP f = 1 kHz f = 1 kHz f = 1 kHz VO = 2 VPP, f = 10 MHz AV = +2 VO = 2 VPP, f = 10 MHz AV = +2 RL = 150Ω AV = +2, NTSC RL = 150Ω AV = +2, NTSC VO = 2 VPP, AV = +2, f = 10 MHz, RL = 150Ω 93 100 75 100 60 35 60 2000 1400 50 5 6 3 16 4 -50 -55 0.05 0.04 0.58 % Deg % pA/√Hz pA/√Hz nV/√Hz dBc 1000 1000 1000 V/µs min ns Limit (Note 6) LM6182I Limit (Note 6) dB MHz Units ts tr, tf tp in(+) in(−) en Settling Time (0.1%) Rise and Fall Time Propagation Delay Time Non-Inverting Input Noise Current Density Inverting Input Noise Current Density Input Noise Voltage Density Second Harmonic Distortion Third Harmonic Distortion Differential Gain Differential Phase THD Total Harmonic Distortion www.national.com 4 ± 5V DC Electrical Characteristics The following specifications apply for supply voltage = ± 5V, Vcm = VO = 0V, Rf = 820Ω, and RL = 1 kΩ unless otherwise noted. Boldface limits apply at the temperature extremes; all other limits TJ = 25˚C. Symbol Parameter Conditions Typical (Note 5) LM6182AM LM6182AI Limit (Note 6) VOS TCVOS IB Input Offset Voltage Input Offset Voltage Drift Inverting Input Bias Current Non-Inverting Input Bias Current TCIB IB PSR Inverting Input Bias Current Drift Non-Inverting Input Bias Current Drift Inverting Input Bias Current Power Supply Rejection Non-Inverting Input Bias Current Power Supply Rejection IB CMR Inverting Input Bias Current Common Mode Rejection Non-Inverting Input Bias Current Common Mode Rejection CMRR PSRR RO RIN VO Common Mode Rejection Ratio Power Supply Rejection Ratio Output Resistance Non-Inverting Input Resistance Output Voltage Swing RL = 1 kΩ RL = 150Ω ISC ZT Output Short Circuit Current Transimpedance RL = 1 kΩ RL = 150Ω IS VCM Supply Current Input Common Mode Voltage Range No Load, VIN = 0V Both Amplifiers V+−1.7V V−+1.7V −2.5V ≤ VCM ≤ +2.5V 57 80 0.25 8 2.6 2.2 100 1.4 1.0 13 2.25 2.0 2.0 1.8 65 35 0.75 0.3 0.5 0.2 17 18.5 2.25 2.0 2.0 1.8 65 40 0.75 0.35 0.5 0.25 17 18.5 2.25 2.0 2.0 1.8 65 40 0.6 0.3 0.4 0.2 17 18.5 mA max V mA min MΩ min −2.5V ≤ VCM ≤ +2.5V 0.12 −2.5V ≤ VCM ≤ +2.5V 0.3 1.0 2.5 5.0 0.25 50 3.0 10 22 1.5 3.0 10 22 1.5 3.0 17.5 27.0 3.0 5.0 nA/˚C 0.5 1.0 0.5 1.0 0.5 1.0 0.5 1.0 50 47 70 67 AV = −1 f = 300 kHz 0.5 1.0 0.5 1.0 0.5 1.0 0.5 1.0 50 47 70 67 0.75 1.5 0.5 1.5 1.0 1.5 0.5 1.5 50 47 64 60 Ω MΩ V min dB min µA/V max 2.0 3.0 Limit (Note 6) 2.0 2.5 LM6182I Limit (Note 6) 3.0 3.5 mV max µV/˚C µA max Units ± 4V ≤ VS ≤ ± 6V ± 4V ≤ VS ≤ ± 6V 0.3 0.05 ± 4V ≤ VS ≤ ± 6V 5 www.national.com ± 5V AC Electrical Characteristics The following specifications apply for supply voltage = ± 5V, Vcm = VO = 0V, Rf = 820Ω, and RL = 1 kΩ unless otherwise noted. Boldface limits apply at the temperature extremes; all other limits TJ = 25˚C. Symbol Parameter Conditions Typical (Note 5) LM6182AM Limit (Note 6) Xt BW Crosstalk Rejection Closed Loop Bandwidth −3 dB (Note 7) AV = +2 AV = +10 AV = −1 Closed Loop Bandwidth 0.1 dB Flat, RSOURCE = 200Ω PBW SR ts tr, tf tp in(+) in(−) en Power Bandwidth Slew Rate Settling Time (0.1%) Rise and Fall Time Propagation Delay Time Non-Inverting Input Noise Current Density Inverting Input Noise Current Density Input Noise Voltage Density Second Harmonic Distortion Third Harmonic Distortion Differential Gain Differential Phase THD Total Harmonic Distortion AV = −10 AV = +2, RL = 150Ω AV = −1, VO = 4 VPP AV = −1, VO = ± 2V RL = 150Ω, (Note 8) AV = −1, VO = ± 2V RL = 150Ω VO = 1 VPP VO = 1 VPP f = 1 kHz f = 1 kHz f = 1 kHz VO = 2 VPP, f = 10 MHz AV = +2 VO = 2 VPP, f = 10 MHz AV = +2 RL = 150Ω AV = +2, NTSC RL = 150Ω AV = +2, NTSC VO = 2 VPP, AV = +2, f = 5 MHz, RL = 150Ω 92 50 40 55 35 15 40 500 50 8.5 8 3 16 4 -45 -55 0.06 0.16 0.36 % Deg % pA/√Hz pA/√Hz nV/√Hz dBc 375 375 375 V/µs min ns LM6182AI Limit (Note 6) LM6182I Limit (Note 6) dB MHz Units 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 device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: Human body model 100 pF and 1.5 kΩ. Note 3: The typical junction-to-ambient thermal resistance of the molded plastic DIP(N) soldered directly into a PC board is 95˚C/W. The junction-to-ambient thermal resistance of the S.O. surface mount (M) package mounted flush to the PC board is 70˚C/W when pins 1,4,8,9 and 16 are soldered to a total of 2 in2 1 oz copper trace. The S.O. (M) package must have pin 4 and at least one of pins 1,8,9, or 16 connected to V− for proper operation. Note 4: Continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowable junction temperature of 150˚C. Each amplifier of the LM6182 is short circuit current limited to 100 mA typical. Note 5: Typical values represent the most likely parametric norm. Note 6: All limits are guaranteed at room temperature (standard type face) or at operating temperature extremes (boldface type). Note 7: Each amp excited in turn with 100 kHz to produce Vo = 2 Vpp. Results are input referred. Note 8: Measured from +25% to +75% of output waveform. Note 9: Also available per the Standard Military Drawing, 5962-9460301MCA. Note 10: For guaranteed military specifications see military datasheet MNLM6182AM-X. www.national.com 6 ± 5V AC Electrical Characteristics (Continued) Simplified Schematic 1/2 LM6182 DS011926-6 7 www.national.com Typical Performance Characteristics MAXIMUM POWER DERATING CURVES N-Package M-Package DS011926-7 DS011926-8 pins 1, 8, 9 and 16 *θja = Thermal Resistance with 2 square inches of 1 ounce copper tied to TYPICAL PERFORMANCE TEST CIRCUITS Non-Inverting: Small Signal Pulse Response, Slew Rate, −3 dB Bandwidth Inverting: Small Signal Pulse Response, Slew Rate, −3 dB Bandwidth DS011926-9 DS011926-10 www.national.com 8 TYPICAL PERFORMANCE TEST CIRCUITS Amplifier-to-Amplifier Isolation (Continued) Input Voltage Noise DS011926-12 DS011926-11 CMRR PSRR (VS+) DS011926-13 DS011926-14 9 www.national.com Typical Performance Characteristics Inverting Gain Frequency Response VS = ± 15V, AV = −1, Rf = 820Ω VS = ± 15V and TA = 25˚C unless otherwise noted. Non-Inverting Gain Frequency Response VS = ± 15V, AV = +2, Rf = 820Ω Inverting Gain Frequency Response VS = ± 5V, AV = −1, Rf = 820Ω DS011926-52 DS011926-53 DS011926-54 Non-Inverting Gain Frequency Response VS = ± 5V, AV = +2, Rf = 820Ω −3 dB Bandwidth vs Rf and Rs, AV = +2 Inverting Gain vs −3 dB Bandwidth Rf = 820Ω DS011926-56 DS011926-55 DS011926-57 Non-Inverting Gain vs −3 dB Bandwidth Rf = 820Ω −3 dB Bandwidth vs Supply Voltage AV = −1 Transimpedance vs Frequency RL = 1 kΩ DS011926-58 DS011926-59 DS011926-60 www.national.com 10 Typical Performance Characteristics noted. (Continued) Transimpedance vs Frequency RL = 150Ω VS = ± 15V and TA = 25˚C unless otherwise Settling Response VS = ± 15V, RL = 150Ω AV = −1, VO = ± 5V DS011926-61 DS011926-62 Settling Response VS = ± 5V, RL = 150Ω AV = −1, VO = ± 2V Long Term Settling Time Response VS = ± 15V, RL = 150Ω, AV = −1, VO = ± 5V Suggested Rf and Rs for CL, AV = −1 DS011926-63 DS011926-64 DS011926-65 Suggested Rf and Rs for CL, AV = +2 Output Impedance vs Frequency AV = −1, RL = 820Ω PSRR (VS+) vs Frequency, AV = 2, Rf = Rs = 820Ω DS011926-66 DS011926-67 DS011926-68 11 www.national.com Typical Performance Characteristics noted. (Continued) PSRR (VS−) vs Frequency, AV = 2, Rf = Rs = 820Ω VS = ± 15V and TA = 25˚C unless otherwise CMRR vs Frequency Rf = Rs = 820Ω Input Voltage Noise vs Frequency DS011926-70 DS011926-69 DS011926-71 Input Current Noise vs Frequency Slew Rate vs Temperature AV = −1, RL = 150Ω Slew Rate vs Supply Voltage AV = −1, RL = 150Ω DS011926-72 DS011926-73 DS011926-74 Distortion vs Frequency VS = ± 15V, AV = +2, RL = 150Ω, VO = 2Vp-p Distortion vs Frequency VS = ± 15V, AV = −1, RL = 150Ω, VO = 2Vp-p Distortion vs Frequency VS = ± 5V, AV = +2, RL = 150Ω, VO = 2Vp-p DS011926-75 DS011926-76 DS011926-77 www.national.com 12 Typical Performance Characteristics noted. (Continued) Distortion vs Frequency VS = ± 5V, AV = −1, RL = 150Ω, VO = 2Vp-p VS = ± 15V and TA = 25˚C unless otherwise Crosstalk Rejection vs Frequency Maximum Output Voltage Swing vs Frequency (THD ≤ 1%) DS011926-79 DS011926-78 DS011926-80 −3 dB Bandwidth vs Temperature, AV = −1 −3 dB Bandwidth vs Temperature, AV = +2 Small Signal Pulse Response vs Temperature, AV = −1, VS = ± 15V, RL = 1 kΩ DS011926-81 DS011926-82 DS011926-83 Small Signal Pulse Response vs Temperature, AV = −1, VS = ± 15V, RL = 150Ω Small Signal Pulse Response vs Temperature, AV = +2, VS = ± 15V, RL = 1 kΩ Small Signal Pulse Response vs Temperature, AV = +2, VS = ± 15V, RL = 150Ω DS011926-84 DS011926-85 DS011926-86 13 www.national.com Typical Performance Characteristics noted. (Continued) Settling Time vs Output Step, RF = 820Ω RL = 150Ω, AV = −1 VS = ± 15V and TA = 25˚C unless otherwise Settling Time vs Output Step, RF = 820Ω RL = 150Ω, AV = −1 Small Signal Pulse Response vs Closed-Loop Gain RL = 1k DS011926-87 DS011926-88 DS011926-89 Small Signal Pulse Response vs Closed-Loop Gain RL = 150Ω Small Signal Pulse Response vs Supply Voltage AV = +2, RL = 1k VOS vs Temperature DS011926-92 DS011926-90 DS011926-91 Zt vs Temperature Zt vs Temperature Is vs Temperature DS011926-93 DS011926-94 DS011926-95 www.national.com 14 Typical Performance Characteristics noted. (Continued) PSRR vs Temperature VS = ± 15V and TA = 25˚C unless otherwise CMRR vs Temperature Ib (+) vs Temperature DS011926-96 DS011926-97 DS011926-98 Ib (−) vs Temperature Ib (+) PSR vs Temperature Ib (−) PSR vs Temperature DS011926-99 DS011926-A0 DS011926-A1 Ib (+) CMR vs Temperature Ib (−) CMR vs Temperature Isc( ± ) vs Temperature DS011926-A2 DS011926-A3 DS011926-A4 Output Swing vs Temperature Output Swing vs Temperature DS011926-A5 DS011926-A6 15 www.national.com Typical Applications CURRENT FEEDBACK TOPOLOGY For a conventional voltage feedback amplifier the resulting small-signal bandwidth is inversely proportional to the desired gain to a first order approximation based on the gain-bandwidth concept. In contrast, the current feedback amplifier topology, such as the LM6182, transcends this limitation to offer a signal bandwidth that is relatively independent of the closed loop gain. Figure 1A and Figure 1B illustrate that for closed loop gains of −1 and −5 the resulting pulse fidelity suggests quite similiar bandwidths for both configurations. DS011926-22 FIGURE 2. Rf Sets Amplifier Bandwidth and Rs is Adjusted to Obtain the Desired Closed-Loop Gain, AV. Although this Rf value will provide good results for most applications, it may be advantageous to adjust this value slightly. Consider, for instance, the effect on pulse responses with two different configurations where both the closed-loop gains are +2 and the feedback resistors are 820Ω, and 1640Ω, respectively. Figure 3A and Figure 3B illustrate the effect of increasing Rf while maintaining the same closed-loop gain – the amplifier bandwidth decreases. Accordingly, larger feedback resistors can be used to slow down the LM6182 and reduce overshoot in the time domain response. Conversely, smaller feedback resistance values than 820Ω can be used to compensate for the reduction of bandwidth at high closed-loop gains, due to 2nd order effects. For example Figure 4A and Figure 4B illustrate reducing Rf to 500Ω to establish the desired small signal response in an amplifier configured for a closed-loop gain of +25. DS011926-20 1A. AV = −1 DS011926-21 1B. AV = −5 FIGURE 1. Variation of Closed-Loop Gain from −1 to −5 Yields Similar Responses. FEEDBACK RESISTOR SELECTION: Rf Selecting the feedback resistor, Rf, is a dominant factor in compensating the LM6182. For general applications the LM6182 will maintain specified performance with an 820Ω feedback resistor. The closed-loop bandwidth of the LM6182 depends on the feedback resistance, Rf. Therefore, Rs, and not Rf, is varied to adjust for the desired closed-loop gain as demonstrated in Figure 2. DS011926-23 3A. Rf = 820Ω DS011926-24 3B. Rf = 1640Ω FIGURE 3. Increase Compensation by Increasing Rf, AV = +2 www.national.com 16 Typical Applications (Continued) bandwidth leading to possible instability. Capacitive feedback should therefore not be used because the impedance of a capacitor decreases with increasing frequency. DS011926-25 4A. Rf = 820Ω DS011926-28 FIGURE 6. Current Feedback Amplifiers are Unstable with Capacitive Feedback For voltage feedback amplifiers it is quite common to place a small lead compensation capacitor in parallel with feedback resistance, Rf. This compensation serves to reduce the amplifier’s peaking. One application of the lead compensation capacitor is to counteract the effects of stray capacitance from the inverting input to ground in circuit board layouts. The LM6182 current feedback amplifier does not require this lead compensation capacitor and has an even simpler, more elegant solution. To limit the bandwidth and peaking of the LM6182 current feedback amplifier, do not use a capacitor across Rf as in Figure 7. This actually has the opposite effect and extends the bandwidth of the amplifier leading to possible instability. Instead, simply increase the value of the feedback resistor as shown in Figure 3. Non-inverting applications can also reduce peaking and limit bandwidth by adding an RC circuit as illustrated in Figure 8. DS011926-26 4B. Rf = 500Ω FIGURE 4. , 4B. Reducing Rf to Increase Bandwidth for Large Closed-Loop Gains, AV = +25 The extent of the amplifier’s dependence on Rf is displayed in Figure 5 for one particular closed-loop gain. DS011926-27 FIGURE 5. −3 dB Bandwidth Is Determined By Selecting Rf. CAPACITIVE FEEDBACK Current feedback amplifiers rely on feedback impedance for proper compensation. Even in unity gain current feedback amplifiers require a feedback resistor. LM6182 performance is specified for a feedback resistance of 820Ω. Decreasing the feedback impedance below 820Ω extends the amplifier’s DS011926-29 FIGURE 7. Compensation Capacitors Are Not Used with the LM6182, Instead Simply Increase Rf to Compensate 17 www.national.com Typical Applications (Continued) DRIVING CAPACITIVE LOADS The LM6182 can drive significantly larger capacitive loads than many current feedback amplifiers. This is extremely valuable for simplifying the design of coax-cable drivers. Although the LM6182 can directly drive as much as 100 pF of load capacitance without oscillating, the resulting response will be a function of the feedback resistor value. Figure 9B illustrates the small-signal pulse response of the LM6182 while driving a 50 pF load. Ringing persists for approximately 100 ns. To achieve pulse responses with less ringing either the feedback resistor can be increased (see Typical Performance Characteristics “Suggested Rf and Rs for CL”), or resistive isolation can be used (10Ω–51Ω typically works well). Either technique, however, results in lowering the system bandwidth. Figure 10B illustrates the improvement obtained by using a 47Ω isolation resistor. DS011926-30 8A DS011926-32 9A DS011926-31 8B FIGURE 8. RC Limits Amplifier Bandwidth to 50 MHz, Eliminating Peaking in the Resulting Pulse Response as Compared to Figure 3A SLEW RATE CONSIDERATIONS The slew rate characteristics of current feedback amplifiers are different than traditional voltage feedback amplifiers. In voltage feedback amplifiers, slew rate limiting or non-linear amplifier behavior is dominated by the finite availability of the 1st stage tail current charging the compensation capacitor. The slew rate of current feedback amplifiers, in contrast, is not constant. Transient current at the inverting input is proportional to the current available to the amplifier’s compensation capacitor. The current feedback amplifier is therefore not traditionally slew rate limited. This enables large slew rates responses of 2000 V/µs. The non-inverting configuration slew rate is also determined by input stage limitations. Accordingly, variations of slew rates occur for different circuit topologies. DS011926-33 9B FIGURE 9. AV = −1, LM6182 Can Directly Drive 50 pF of Load Capacitance with 100 ns of Ringing Resulting in Pulse Response www.national.com 18 Typical Applications (Continued) of the S.O. package are not needed, pin 4 and at least one of pins 1,8,9, or 16 must be connected to V− for proper operation. Figure 11 shows recommended copper patterns used to dissipate heat from the LM6182. DS011926-34 10A DS011926-36 8-pin DIP (N) DS011926-35 10B FIGURE 10. Resistive Isolation of CL Provides Higher Fidelity Pulse Response. Rf and Rs Could Also Be Increased to Maintain AV = −1 and Improve Pulse Response Characteristics. POWER SUPPLY BYPASSING AND LAYOUT CONSIDERATIONS A fundamental requirement for high-speed amplifier design is adequate bypassing of the power supply. It is critical to maintain a wideband low-impedance to ground at the amplifiers supply pins to insure the fidelity of high speed amplifier transient signals. 0.1 µF ceramic bypass capacitors at each supply pin are sufficient for many applications. Typically 10 µF tantalum capacitors are also required if large current transients are delivered to the load. The bypass capacitors should be placed as close to the amplifier pins as possible, such as 0.5" or less. Applications requiring high output power, cable drivers for example, cause increased internal power dissipation. Internal power dissipation can be minimized by operating at reduced power supply voltages, such as ± 5V. Optimum heat dissipation is achieved by using wide circuit board traces and soldering the part directly onto the board. Large power supply and ground planes will improve power dissipation. Safe Operating Area (S.O.A.) is determined using the Maximum Power Derating Curves. The 16-pin small outline package (M) has 5 V− heat sinking pins that enable a junction-to-ambient thermal resistance of 70˚C/W when soldered to 2 in2 1 oz. copper trace. A V− heat sinking pin is located on each corner of the package for ease of layout. This allows high output power and/or operation at elevated ambient temperatures without the additional cost of an integrated circuit heat sink. If the heat sinking capabilities DS011926-37 16-pin S.O. (M) FIGURE 11. Copper Heatsink Layouts CROSSTALK REJECTION The LM6182 has an excellant crosstalk rejection value of 62 dB at 10 MHz. This value is made possible because the LM6182 amplifiers share no common circuitry other than the supply. High frequency crosstalk that does appear is primarily caused by the magnetic and capacitive coupling of the internal bond wires. Bond wires connect the die to the package lead frame. The amount of current flowing through the bond wires is proportional to the amount of crosstalk. Therefore, crosstalk rejection ratings will degrade when driving heavy loads. Figure 12 and shows a 10 dB difference for two different loads. 19 www.national.com Typical Applications (Continued) DS011926-41 DS011926-38 FIGURE 12. Crosstalk Rejection The LM6182 crosstalk effect is minimized in applications that cascade the amplifiers by preceding amplifier A with amplifier B. START-UP TIME Using the circuit in Figure 13, the LM6182 demonstrated a start-up time of 50 ns. DS011926-42 FIGURE 14. Open Loop Overdrive Recovery Times of 5 ns and 30 ns The large closed-loop gain configuration in Figure 15 forces the amplifier output into overdrive. The typical recovery time to a linear output value is 15 ns. DS011926-39 FIGURE 13. Start-Up Test Circuit OVERDRIVE RECOVERY The LM6182 is an excellent choice for high speed applications needing fast overdrive recovery. Nanosecond recovery times allow the LM6182 to protect subsequent stages from excessive input saturation and possible damage. When the output or input voltage range of a high speed amplifier is exceeded, the amplifier must recover from an overdrive condition. The non-linear output voltage remains as long as the overdrive condition persists. Linear operation resumes after the overdrive condition is removed. Overdrive recovery time is the delay before an amplifier returns to linear operation. The typical recovery times for exceeding open loop, closed loop, and input commom-mode voltage ranges are illustrated in Figures 14, 15, 16. The open-loop circuit of Figure 14 generates an overdrive response by allowing the ± 0.5V input to exceed the linear input range of the amplifier. Typical positive and negative overdrive recovery times are 5 ns and 30 ns, respectively. DS011926-43 DS011926-44 FIGURE 15. 15 ns Closed Loop Output Overdrive Recovery Time Generated by Saturating the Output Stage of the LM6182 www.national.com 20 Typical Applications (Continued) The common-mode input range of a unity-gain circuit is exceeded by a 4V pulse resulting in a typical recovery time of 20 ns shown in Figure 16. NON-INVERTING GAIN AMPLIFIER Current feedback amplifiers can be used in non-inverting gain and level shifting functions. The same basic closed-loop gain equation used for voltage feedback amplifiers applies to current feedback amplifiers: 1 + Rf/Rs. DS011926-48 DS011926-45 FIGURE 18. Non-Inverting Closed Loop Gain is Determined with the Same Equation Voltage Feedback Amplifiers Use: 1 + Rf/Rs INVERTING GAIN AMPLIFIER The inverting closed loop gain equation used with voltage feedback amplifiers also applies to current feedback amplifiers. DS011926-49 DS011926-46 FIGURE 16. Output Recovery from an Input that Exceeds the Common-Mode Range SPICE MACROMODEL A spice macromodel is available for the LM6182. Contact your local National Semiconductor sales office to obtain an operational amplifier spice model library disk. FIGURE 19. Current Feedback Amplifiers Can Be Used for Inverting Gains, Just Like a Voltage Feedback Amplifier: −Rf/Rs SUMMING AMPLIFIER The current feedback topology of the LM6182 provides significant performance advantages over a conventional voltage feedback amplifier used in a standard summing circuit. Using a voltage feedback amplifier, the bandwidth of the summing circuit in Figure 20 is limited by the highest gain needed for either signal V1 or V2. If the LM6182 amplifier is used instead, wide circuit bandwidth can be maintained relatively independent of gain requirements. Typical Application Circuits UNITY GAIN AMPLIFIER The LM6182 current feedback amplifier is unity gain stable. The feedback resistor, Rf, is required to maintain the LM6182’s dynamic performance. DS011926-50 DS011926-47 FIGURE 17. LM6182 Is Unity Gain Stable FIGURE 20. LM6182 Allows the Summing Circuit to Meet the Requirements of Wide Bandwidth Systems Independent of Signal Gain 21 www.national.com Ordering Information Package Temperature Range Military −55˚C to +125˚C 8-pin Molded DIP 16-pin Small Outline If Military/Aerospace specified devices are required, contact the National Semiconductor Sales Office or Distributors for availability and specifications. Industrial −40˚C to +85˚C LM6182AIN LM6182IN LM6182AIM LM6182IM NSC Drawing LM6182AMN N08E M16A www.national.com 22 Physical Dimensions inches (millimeters) unless otherwise noted 14-Lead Dual-In-Line Package (J) Order Number LM6182AMJ/883 NS Package Number J14A Small Outline Package (M) Order Number LM6182IM or LM6182AIM NS Package Number M16A 23 www.national.com LM6182 Dual 100 mA Output, 100 MHz Current Feedback Amplifier Physical Dimensions inches (millimeters) unless otherwise noted (Continued) Dual-In-Line Package (N) Order Number LM6182IN, LM6182AIN, or LM6182AMN 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 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.