LM6181IM-8

LM6181 100 mA, 100 MHz Current Feedback Amplifier May 1998 LM6181 100 mA, 100 MHz Current Feedback Amplifier General Description The LM6181 current-feedback amplifier offers an unparalleled combination of bandwidth, slew-rate, and output current. The amplifier can directly drive up to 100 pF capacitive loads without oscillating and a 10V 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 an 8-pin DIP high-speed amplifier making it ideal for video applications. Built on National’s advanced high-speed VIP™ II (Vertically Integrated PNP) process, the LM6181 employs currentfeedback providing bandwidth that does not vary dramatically with gain; 100 MHz at AV = −1, 60 MHz at AV = −10. With a slew rate of 2000V/µs, 2nd harmonic distortion of −50 dBc at 10 MHz and settling time of 50 ns (0.1%) the LM6181 dynamic performance makes it ideal for data acquisition, high speed ATE, and precision pulse amplifier applications. Features (Typical unless otherwise noted) n Slew rate: 2000 V/µs n Settling time (0.1%): 50 ns n Characterized for supply ranges: ± 5V and ± 15V n Low differential gain and phase error: 0.05%, 0.04˚ n High output drive: ± 10V into 100Ω n Guaranteed bandwidth and slew rate n Improved performance over EL2020, OP160, AD844, LT1223 and HA5004 Applications n n n n n Coax cable driver Video amplifier Flash ADC buffer High frequency filter Scanner and Imaging systems Typical Application DS011328-1 Cable Driver DS011328-2 VIP™ is a registered trademark of National Semiconductor Corporation. © 1999 National Semiconductor Corporation DS011328 www.national.com 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 Soldering Information Dual-In-Line Package (N) Soldering (10 sec) Small Outline Package (M) Vapor Phase (60 seconds) Infrared (15 seconds) Output Short Circuit Storage Temperature Range Maximum Junction Temperature ESD Rating (Note 2) −65˚C ≤ TJ ≤ +150˚C 150˚C ± 3000V ± 18V ± 6V ± Supply Voltage 15 mA Operating Ratings Supply Voltage Range 7V to 32V Junction Temperature Range (Note 3) LM6181AM −55˚C ≤ TJ ≤ +125˚C LM6181AI, LM6181I −40˚C ≤ TJ ≤ +85˚C Thermal Resistance (θJA, θJC) 8-pin DIP (N) 102˚C/W, 42˚C/W 8-pin SO (M-8) 153˚C/W, 42˚C/W 16-pin SO (M) 70˚C/W, 38˚C/W 260˚C 215˚C 220˚C (Note 7) ± 15V DC Electrical Characteristics The following specifications apply for Supply Voltage = ± 15V, 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 LM6181AM Typical (Note 4) VOS TC VOS IB Input Offset Voltage Input Offset Voltage Drift Inverting Input Bias Current Non-Inverting Input Bias Current TC IB Inverting Input Bias Current Drift Non-Inverting Input Bias Current Drift IB PSR 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 = 100Ω ISC Output Short Circuit Current −10V ≤ VCM ≤ +10V VS = ± 4.5V, ± 16V AV = −1, f = 300 kHz 60 80 0.2 10 12 11 130 11 11 10 7.5 100 75 130 11 −10V ≤ VCM ≤ +10V 0.1 −10V ≤ VCM ≤ +10V 0.3 VS = ± 4.5V, ± 16V 0.05 VS = ± 4.5V, ± 16V 0.3 0.5 3.0 0.5 1.5 0.5 0.75 0.5 0.5 50 50 70 70 0.2 10 12 11 11 10 8.0 100 85 130 11 80 60 0.1 0.3 0.05 0.3 0.5 3.0 0.5 1.5 0.5 0.75 0.5 0.5 50 50 70 70 0.2 10 12 11 11 10 8.0 100 85 mA min 80 60 0.1 0.3 0.05 0.3 0.75 4.5 0.5 3.0 0.75 1.0 0.5 0.5 50 50 70 65 dB min dB min Ω MΩ min V min µA/V max 2.0 5.0 2.0 0.5 30 10 5.0 12.0 1.5 3.0 30 10 0.5 Limit (Note 5) 3.0 4.0 5.0 2.0 5.0 12.0 1.5 3.0 30 10 2.0 LM6181AI Typical (Note 4) 2.0 Limit (Note 5) 3.0 3.5 5.0 5.0 10 17.0 3.0 5.0 nA/˚C LM6181I Typical (Note 4) 3.5 Limit (Note 5) 5.0 5.5 mV max µV/˚C µA max Units www.national.com 2 ± 15V DC Electrical Characteristics Symbol Parameter Conditions (Continued) The following specifications apply for Supply Voltage = ± 15V, RF = 820Ω, and RL = 1 kΩ unless otherwise noted. Boldface limits apply at the temperature extremes; all other limits TJ = 25˚C. LM6181AM Typical (Note 4) ZT Transimpedance RL = 1 kΩ RL = 100Ω IS VCM Supply Current Input Common Mode Voltage Range No Load, VO = 0V 1.8 1.4 7.5 V+ − 1.7V V− + 1.7V Limit (Note 5) 1.0 0.5 0.8 0.4 10 10 V+ − 1.7V V− + 1.7V 7.5 1.4 LM6181AI Typical (Note 4) 1.8 Limit (Note 5) 1.0 0.5 0.8 0.4 10 10 V+ − 1.7V V− + 1.7V 7.5 1.4 LM6181I Typical (Note 4) 1.8 Limit (Note 5) 0.8 0.4 0.7 0.35 10 10 mA max V MΩ min Units ± 15V AC Electrical Characteristics The following specifications apply for Supply Voltage = ± 15V, RF = 820Ω, RL = 1 kΩ unless otherwise noted. Boldface limits apply at the temperature extremes; all other limits TJ = 25˚C. Symbol Parameter Conditions LM6181AM Typical (Note 4) BW Closed Loop Bandwidth −3 dB AV = +2 AV = +10 AV = −1 AV = −10 PBW SR Power Bandwidth Slew Rate AV = −1, VO = 5 VPP Overdriven AV = −1, VO = ± 10V, RL = 150Ω (Note 6) 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 f = 1 kHz 2 VPP, 10 MHz 2 VPP, 10 MHz RL = 150Ω AV = +2 NTSC Differential Phase RL = 150Ω AV = +2 NTSC 0.04 0.04 0.04 Deg 0.05 0.05 0.05 % 4 −50 −55 4 −50 −55 4 −50 −50 dBc f = 1 kHz 16 16 16 AV = −1, VO = ± 5V RL = 150Ω VO = 1 VPP VO = 1 VPP f = 1 kHz 5 6 3 5 6 3 5 6 3 50 50 50 ns 100 80 100 60 60 2000 1400 1000 80 Limit (Note 5) LM6181AI Typical (Note 4) 100 80 100 60 60 2000 1400 1000 80 Limit (Note 5) LM6181I Typical (Note 4) 100 80 100 60 60 2000 1400 1000 V/µs min 80 Limit (Note 5) MHz min Units 3 www.national.com ± 5V DC Electrical Characteristics The following specifications apply for Supply Voltage = ± 5V, 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 LM6181AM Typical (Note 4) VOS TC VOS IB Input Offset Voltage Input Offset Voltage Drift Inverting Input Bias Current Non-Inverting Input Bias Current TC IB Inverting Input Bias Current Drift Non-Inverting Input Bias Current Drift IB PSR 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 = 100Ω ISC ZT Output Short Circuit Current Transimpedance RL = 1 kΩ RL = 100Ω IS VCM Supply Current Input Common Mode Voltage Range No Load, VO = 0V 1.4 1.0 6.5 V+ − 1.7V V− + 1.7V 2.6 2.2 100 2.25 2.2 2.0 2.0 75 70 0.75 0.35 0.5 0.25 8.5 8.5 V+ − 1.7V V− + 1.7V 6.5 1.0 1.4 100 2.2 2.6 2.25 2.25 2.0 2.0 75 70 0.75 0.4 0.5 0.25 8.5 8.5 V+ − 1.7V V− + 1.7V 6.5 1.0 1.0 100 2.2 2.6 2.25 2.25 2.0 2.0 75 70 0.6 0.3 0.4 0.2 8.5 8.5 mA max V MΩ min mA min AV = −1, f = 300 kHz 0.25 8 VS = ± 4.0V, ± 6.0V 80 −2.5V ≤ VCM ≤ +2.5V 57 1.0 50 47 70 70 0.25 8 80 57 0.5 50 47 70 70 0.25 8 80 57 0.5 50 47 64 64 Ω MΩ min V min dB min −2.5V ≤ VCM ≤ +2.5V 0.12 −2.5V ≤ VCM ≤ +2.5V 0.3 0.5 0.5 1.0 0.5 0.12 0.3 0.5 0.5 1.0 0.5 0.12 0.3 0.5 1.0 1.5 0.5 VS = ± 4.0V, ± 6.0V 0.05 VS = ± 4.0V, ± 6.0V 0.3 0.5 0.5 0.5 0.05 0.3 0.5 0.5 0.5 0.05 0.3 1.0 1.0 0.5 µA/V max 3.0 3.0 3.0 50 0.25 1.0 2.5 5.0 10 22 1.5 1.5 50 0.25 Limit (Note 5) 2.0 3.0 2.5 5.0 10 22 1.5 1.5 50 0.25 LM6181AI Typical (Note 4) 1.0 Limit (Note 5) 2.0 2.5 2.5 5.0 17.5 27.0 3.0 5.0 nA/˚C LM6181I Typical (Note 4) 1.0 Limit (Note 5) 3.0 3.5 mV max µV/˚C µA max Units www.national.com 4 ± 5V AC Electrical Characteristics The following specifications apply for Supply Voltage = ± 5V, 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 LM6181AM Typical (Note 4) BW Closed Loop Bandwidth −3 dB AV = +2 AV = +10 AV = −1 AV = −10 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 f = 1 kHz 2 VPP, 10 MHz 2 VPP, 10 MHz RL = 150Ω AV = +2 NTSC Differential Phase RL = 150Ω AV = +2 NTSC Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions 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) package soldered directly into a PC board is 102˚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 2 in2 1 oz. copper trace. The 16-pin 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. The typical junction-to-ambient thermal resistance of the S.O. (M-8) package soldered directly into a PC board is 153˚C/W. Note 4: Typical values represent the most likely parametric norm. Note 5: All limits guaranteed at room temperature (standard type face) or at operating temperature extremes (bold face type). Note 6: Measured from +25% to +75% of output waveform. Note 7: Continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowed junction temperature of 150˚C. Output currents in excess of ± 130 mA over a long term basis may adversely affect reliability. Note 8: For guaranteed Military Temperature Range parameters see RETS6181X. LM6181AI Typical (Note 4) 50 40 Limit (Note 5) LM6181I Typical (Note 4) 50 40 Limit (Note 5) Units Limit (Note 5) 50 40 55 35 40 500 50 8.5 8 3 16 4 −45 −55 0.063 375 35 MHz min 35 55 35 40 500 50 8.5 8 3 16 4 −45 −55 0.063 35 55 35 40 AV = −1, VO = 4 VPP AV = −1, VO = ± 2V, RL = 150Ω (Note 6) AV = −1, VO = ± 2V RL = 150Ω VO = 1 VPP VO = 1 VPP f = 1 kHz f = 1 kHz 375 500 50 8.5 8 3 16 4 −45 −55 0.063 375 V/µs min ns dBc % 0.16 0.16 0.16 Deg 5 www.national.com Typical Performance Characteristics CLOSED-LOOP FREQUENCY RESPONSE VS = ± 15V; Rf = 820Ω; R L = 1 kΩ TA = 25˚C unless otherwise noted CLOSED-LOOP FREQUENCY RESPONSE VS = ± 15V; Rf = 820Ω; RL = 150Ω UNITY GAIN FREQUENCY RESPONSE VS = ± 15V; AV = +1; Rf = 820Ω DS011328-34 DS011328-35 DS011328-36 UNIT GAIN FREQUENCY RESPONSE VS = ± 5V; AV = +1; Rf = 820Ω FREQUENCY RESPONSE vs SUPPLY VOLTAGE AV = −1; Rf = 820Ω; RL = 1 kΩ FREQUENCY RESPONSE vs SUPPLY VOLTAGE AV = −1; Rf = 820Ω; RL = 150Ω DS011328-37 DS011328-38 DS011328-39 INVERTING GAIN FREQUENCY RESPONSE VS = ± 15V; AV = −1; Rf = 820Ω INVERTING GAIN FREQUENCY RESPONSE VS = ± 5V; AV = −1; Rf = 820Ω NON-INVERTING GAIN FREQUENCY RESPONSE VS = ± 15V; AV = +2; Rf = 820Ω DS011328-40 DS011328-41 DS011328-42 www.national.com 6 Typical Performance Characteristics NON-INVERTING GAIN FREQUENCY RESPONSE VS = ± 5V; AV = +2; Rf = 820Ω TA = 25˚C unless otherwise noted (Continued) INVERTING GAIN FREQUENCY RESPONSE VS = ± 15V; AV = −10; Rf = 820Ω INVERTING GAIN FREQUENCY RESPONSE VS = ± 5V; AV = −10; Rf = 820Ω DS011328-43 DS011328-44 DS011328-45 NON-INVERTING GAIN FREQUENCY RESPONSE VS = ± 15V; AV = +10; Rf = 820Ω NON-INVERTING GAIN FREQUENCY RESPONSE VS = ± 5V; AV = +10; Rf = 820Ω NON-INVERTING GAIN FREQUENCY COMPENSATION VS = ± 15V; AV = +2; RL = 150Ω DS011328-46 DS011328-47 DS011328-48 BANDWIDTH vs Rf & RS AV = −1, RL = 1 kΩ OUTPUT SWING vs RLOAD PULSED, VS = ± 15V, IIN = ± 200 µA, VIN+ = 0V TRANSIMPEDANCE vs FREQUENCY VS = ± 15V RL = 1 kΩ DS011328-49 DS011328-50 DS011328-51 7 www.national.com Typical Performance Characteristics TRANSIMPEDANCE vs FREQUENCY VS = ± 15V RL = 100Ω TA = 25˚C unless otherwise noted (Continued) TRANSIMPEDANCE vs FREQUENCY VS = ± 5V RL = 1 kΩ TRANSIMPEDANCE vs FREQUENCY VS = ± 5V RL = 100Ω DS011328-52 DS011328-53 DS011328-54 SETTLING RESPONSE VS = ± 15V; RL = 150Ω; VO = ± 5V; AV = −1 SETTLING RESPONSE VS = ± 5V; RL = 150Ω; VO = ± 2V; AV = −1 SUGGESTED Rf and RS for CL AV = − 1; RL = 150Ω DS011328-55 DS011328-56 DS011328-57 SUGGESTED Rf and RS FOR CL AV = −1 SUGGESTED Rf and RS FOR CL AV = +2; RL = 150Ω SUGGESTED Rf and RS FOR CL AV = +2 DS011328-58 DS011328-59 DS011328-60 www.national.com 8 Typical Performance Characteristics OUTPUT IMPEDANCE vs FREQ VS = ± 15V; AV = −1 Rf = 820Ω TA = 25˚C unless otherwise noted (Continued) OUTPUT IMPEDANCE vs FREQ VS = ± 5V; AV = −1 Rf = 820Ω PSRR (VS+) vs FREQUENCY DS011328-63 DS011328-61 DS011328-62 PSRR (VS−) vs FREQUENCY CMRR vs FREQUENCY INPUT VOLTAGE NOISE vs FREQUENCY DS011328-64 DS011328-65 DS011328-66 INPUT CURRENT NOISE vs FREQUENCY SLEW RATE vs TEMPERATURE AV = −1; RL = 150Ω, VS = ± 15V SLEW RATE vs TEMPERATURE AV = −1; RL = 150Ω, VS = ± 5V DS011328-67 DS011328-68 DS011328-69 9 www.national.com Typical Performance Characteristics −3 dB BANDWIDTH vs TEMPERATURE AV = −1 TA = 25˚C unless otherwise noted (Continued) SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +1 VS = ± 15V; RL = 1 kΩ SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +1 VS = ± 15V; RL = 100Ω DS011328-70 DS011328-71 DS011328-72 SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +1 VS = ± 5V; RL = 1 kΩ SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +1 VS = ± 5V; RL = 100Ω SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = −1 VS = ± 15V; RL = 1 kΩ DS011328-73 DS011328-74 DS011328-75 SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = −1 VS = ± 15V; RL = 100Ω SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = −1 VS = ± 5V; RL = 1 kΩ SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = −1 VS = ± 5V; RL = 100Ω DS011328-76 DS011328-77 DS011328-78 www.national.com 10 Typical Performance Characteristics SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +2 VS = ± 15V; RL = 1 kΩ TA = 25˚C unless otherwise noted (Continued) SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +2 VS = ± 15V; RL = 100Ω SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +2 VS = ± 5V; RL = 1 kΩ DS011328-79 DS011328-80 DS011328-81 SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +2 VS = ± 5V; RL = 100Ω SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = −10 VS = ± 15V; RL = 1 kΩ SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = −10 VS = ± 15V; RL = 100Ω DS011328-82 DS011328-83 DS011328-84 SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = −10 VS = ± 5V; RL = 1 kΩ SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = −10 VS = ± 5V; RL = 100Ω SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +10 VS = ± 15V; RL = 1 kΩ DS011328-85 DS011328-86 DS011328-87 11 www.national.com Typical Performance Characteristics SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +10 VS = ± 15V; RL = 100Ω TA = 25˚C unless otherwise noted (Continued) SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +10 VS = ± 5V; RL = 1 kΩ SMALL SIGNAL PULSE RESPONSE vs TEMP, AV = +10 VS = ± 5V; RL = 100Ω DS011328-88 DS011328-89 DS011328-90 OFFSET VOLTAGE vs TEMPERATURE OFFSET VOLTAGE vs TEMPERATURE TRANSIMPEDANCE vs TEMPERATURE DS011328-91 DS011328-92 DS011328-93 TRANSIMPEDANCE vs TEMPERATURE QUIESCENT CURRENT vs TEMPERATURE PSRR vs TEMPERATURE DS011328-96 DS011328-94 DS011328-95 www.national.com 12 Typical Performance Characteristics CMRR vs TEMPERATURE TA = 25˚C unless otherwise noted (Continued) INVERTING BIAS CURRENT vs TEMPERATURE NON-INVERTING BIAS CURRENT vs TEMPERATURE DS011328-97 DS011328-98 DS011328-99 PSR IB(+) vs TEMPERATURE PSR IB(−) vs TEMPERATURE CMR IB(+) vs TEMPERATURE DS011328-A1 DS011328-A0 DS011328-A2 CMR IB(−) vs TEMPERATURE ISC(+) vs TEMPERATURE ISC(−) vs TEMPERATURE DS011328-A3 DS011328-A6 DS011328-A4 13 www.national.com Typical Performance Characteristics Absolute Maximum Power Derating Curves DS011328-30 N-Package DS011328-31 *θJA = Thermal Resistance with 2 square inches of 1 ounce Copper tied to Pins 1, 8, 9 and 16. M-Package DS011328-33 M-8 Package www.national.com 14 Typical Performance Characteristics (Continued) Simplified Schematic DS011328-32 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 LM6181, 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 similar bandwidths for both configurations. DS011328-14 FIGURE 2. RS Is Adjusted to Obtain the Desired Closed Loop Gain, AVCL 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. 10 µF tantalum and 0.1 µF ceramic bypass capacitors are recommended for each supply pin. The bypass capacitors should be placed as close to the amplifier pins as possible (0.5" or less). FEEDBACK RESISTOR SELECTION: Rf Selecting the feedback resistor, Rf, is a dominant factor in compensating the LM6181. For general applications the LM6181 will maintain specified performance with an 820Ω feedback resistor. Although this 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 LM6181 (see −3 dB bandwidth vs Rftypical curves) 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 4 illustrates reducing Rf to 500Ω to establish the desired small signal response in an amplifier configured for a closed loop gain of 25. DS011328-12 1a DS011328-13 1b FIGURE 1. 1a, 1b: Variation of Closed Loop Gain from −1 to −5 Yields Similar Responses The closed-loop bandwidth of the LM6181 depends on the feedback resistance, Rf. Therefore, RS and not Rf, must be varied to adjust for the desired closed-loop gain as in Figure 2. www.national.com 16 Typical Applications (Continued) The slew rate of current feedback amplifiers, in contrast, is not constant. Transient current at the inverting input determines slew rate for both inverting and non-inverting gains. The non-inverting configuration slew rate is also determined by input stage limitations. Accordingly, variations of slew rates occur for different circuit topologies. DRIVING CAPACITIVE LOADS The LM6181 can drive significantly larger capacitive loads than many current feedback amplifiers. Although the LM6181 can directly drive as much as 100 pF without oscillating, the resulting response will be a function of the feedback resistor value. Figure 5 illustrates the small-signal pulse response of the LM6181 while driving a 50 pF load. Ringing persists for approximately 70 ns. To achieve pulse responses with less ringing either the feedback resistor can be increased (see typical curves 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. DS011328-15 3a: Rf = 820Ω Figure 6 illustrates the improvement obtained with using a 47Ω isolation resistor. DS011328-18 5a DS011328-16 3b: Rf = 1640Ω FIGURE 3. Increasing Compensation with Increasing Rf DS011328-19 5b FIGURE 5. AV = −1, LM6181 Can Directly Drive 50 pF of Load Capacitance with 70 ns of Ringing Resulting in Pulse Response DS011328-17 FIGURE 4. Reducing Rf for Large Closed Loop Gains, Rf = 500Ω 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. 17 www.national.com Typical Applications (Continued) DS011328-20 6a DS011328-22 7a DS011328-21 6b FIGURE 6. Resistive Isolation of CL Provides Higher Fidelity Pulse Response. Rf and RS Could Be Increased to Maintain AV = −1 and Improve Pulse Response Characteristics. 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 in the frequency domain which equivalently tames the transient response. To limit the bandwidth of current feedback amplifiers, do not use a capacitor across Rf. The dynamic impedance of capacitors in the feedback loop reduces the amplifier’s stability. Instead, reduced peaking in the frequency response, and bandwidth limiting can be accomplished by adding an RC circuit, as illustrated in Figure 7b. DS011328-23 7b FIGURE 7. RC Limits Amplifier Bandwidth to 50 MHz, Eliminating Peaking in the Resulting Pulse Response Typical Performance Characteristics OVERDRIVE RECOVERY When the output or input voltage range of a high speed amplifier is exceeded, the amplifier must recover from an overdrive condition. The typical recovery times for open-loop, closed-loop, and input common-mode voltage range overdrive conditions are illustrated in Figures 9, 11, 11, 12 respectively. The open-loop circuit of Figure 8 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 shown in Figure 9 are 5 ns and 25 ns, respectively. www.national.com 18 Typical Performance Characteristics (Continued) DS011328-26 DS011328-24 FIGURE 10. FIGURE 8. DS011328-27 DS011328-25 FIGURE 9. Open-Loop Overdrive Recovery Time of 5 ns, and 25 ns from Test Circuit in Figure 8 The large closed-loop gain configuration in Figure 10 forces the amplifier output into overdrive. Figure 11 displays the typical 30 ns recovery time to a linear output value. FIGURE 11. Closed-Loop Overdrive Recovery Time of 30 ns from Exceeding Output Voltage Range from Circuit in Figure 10 The common-mode input of the circuit in Figure 10 is exceeded by a 5V pulse resulting in a typical recovery time of 310 ns shown in Figure 12. The LM6181 supply voltage is ± 5V. DS011328-28 FIGURE 12. Exceptional Output Recovery from an Input that Exceeds the Common-Mode Range 19 www.national.com Connection Diagrams (For Ordering Information See Back Page) 16-Pin Small Outline Package (M) 8–Pin Dual-In-Line Package (N)/ Small Outline (M-8) DS011328-3 Order Number LM6181IN, LM6181AIN, LM6181AMN, LM6181AIM-8, LM6181IM-8 or LM6181AMJ/883 See NS Package Number J08A, M08A or N08E DS011328-4 *Heat sinking pins (Note 3) Order Number LM6181IM or LM6181AIM See NS Package Number M16A Ordering Information Package Military −55˚C to +125˚C 8-Pin Molded DIP 8-Pin Small Outline Molded Package 16-Pin Small Outline 8-Pin Ceramic DIP LM6181AMJ/883 LM6181AMN Temperature Range Industrial −40˚C to +85˚C LM6181AIN LM6181IN LM6181AIM-8 LM6181IM-8 LM6181AIM LM6181IM J08A M16A M08A N08E NSC Drawing www.national.com 20 Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead (0.150" Wide) Small Outline Molded Package (M-8) Order Number LM6181AIM-8 or LM6181IM-8 NS Package Number M08A 8-Pin Ceramic Dual-In-Line Package Order Number LM6181AMJ/883 NS Package Number J08A 21 www.national.com Physical Dimensions inches (millimeters) unless otherwise noted (Continued) Small Outline Package (M) Order Number LM6181IM or LM6181AIM NS Package Number M16A Dual-In-Line-Package (N) Order Number LM6181AIN, LM6181IN or LM6181AMN NS Package Number N08E www.national.com 22 LM6181 100 mA, 100 MHz Current Feedback Amplifier Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 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. 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