LT1217

LT1217 Low Power 10MHz Current Feedback Amplifier FEATURES s s s s s s s s s DESCRIPTIO 1mA Quiescent Current 50mA Output Current (Minimum) 10MHz Bandwidth 500V/µs Slew Rate 280ns Settling Time to 0.1% Wide Supply Range, ±5V to ±15V 1mV Input Offset Voltage 100nA Input Bias Current 100MΩ Input Resistance The LT1217 is a 10MHz current feedback amplifier with DC characteristics better than many voltage feedback amplifiers. This versatile amplifier is fast, 280ns settling to 0.1% for a 10V step thanks to its 500V/µs slew rate. The LT1217 is manufactured on Linear Technology’s proprietary complementary bipolar process resulting in a low 1mA quiescent current. To reduce power dissipation further, the LT1217 can be turned off, eliminating the load current and dropping the supply current to 350µA. The LT1217 is excellent for driving cables and other low impedance loads thanks to a minimum output drive current of 50mA. Operating on any supplies from ± 5V to ±15V allows the LT1217 to be used in almost any system. Like other current feedback amplifiers, the LT1217 has high gain bandwidth at high gains. The bandwidth is over 1MHz at a gain of 100. The LT1217 comes in the industry standard pinout and can upgrade the performance of many older products. APPLICATI s s s s s S Video Amplifiers Buffers IF and RF Amplification Cable Drivers 8, 10, 12-Bit Data Acquisition Systems TYPICAL APPLICATI Cable Driver 60 VIN Voltage Gain vs Frequency + LT1217 AMPLIFIER VOLTAGE GAIN (dB) 75Ω 50 40 30 20 10 0 –10 RG = 30Ω RG = 100Ω RG = 330Ω RG = 1.3k RG = ∞ – RF 3k 75Ω CABLE VOUT RG 3k 75Ω R AV = 1 + F RG AT AMPLIFIER OUTPUT. 6dB LESS AT VOUT. LT1217 • TA01 –20 100k U VS = ±15V RF = 3k RL = 100Ω 1M 10M 100M LT1217 • TA02 UO UO FREQUENCY (Hz) 1 LT1217 ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW NULL 1 –IN 2 +IN 3 V– 4 8 SHUTDOWN 7 V+ 6 OUT 5 NULL Supply Voltage ...................................................... ±18V Input Current ...................................................... ±10mA Input Voltage ............................ Equal to Supply Voltage Output Short Circuit Duration (Note 1) ......... Continuous Operating Temperature Range ..................... 0°C to 70°C Storage Temperature Range ................. – 65°C to 150°C Junction Temperature........................................... 150°C Lead Temperature (Soldering, 10 sec.)................. 300°C ORDER PART NUMBER LT1217CN8 LT1217CS8 S8 PART MARKING 1217 N8 PACKAGE S8 PACKAGE 8-LEAD PLASTIC DIP 8-LEAD PLASTIC SOIC LT1217 • POI01 ELECTRICAL CHARACTERISTICS SYMBOL VOS IIN+ IIN– en in RIN CIN CMRR PSRR PARAMETER Input Offset Voltage Non-Inverting Input Current Inverting Input Current Input Noise Voltage Density Input Noise Current Density Input Resistance Input Capacitance Input Voltage Range Common Mode Rejection Ratio Inverting Input Current Common Mode Rejection Power Supply Rejection Ratio VS = ± 15V, TA = 0°C to 70°C unless otherwise noted. CONDITIONS VCM = 0V VCM = 0V VCM = 0V f = 1kHz, RF = 1k, RG = 10Ω f = 1kHz, RF = 1k, RG = 10Ω VIN = ±10V q q q q MIN TYP ±1 ± 100 ± 100 6.5 0.7 MAX ±3 ± 500 ± 500 UNITS mV nA nA nV/√Hz pA/√Hz MΩ pF V dB 20 ± 10 60 68 100 1.5 ± 12 66 5 76 2 10 20 50 20 q VCM = ±10V VCM = ±10V VS = ± 4.5V to ±18V VS = ± 4.5V to ±18V VS = ±4.5V to ±18V RLOAD = 2k, VOUT = ±10V RLOAD = 400Ω, VOUT = ±10V RLOAD = 2k, VOUT = ±10V RLOAD = 400Ω, VOUT = ±10V RLOAD = 2k RLOAD = 200Ω RLOAD = 0Ω RF = 3k, RG = 3k RF = 3k, RG = 3k, VOUT = 100mV RF = 3k, RG = 3k, VOUT = 1V RF = 3k, RG = 3k, VOUT = 1V RF = 3k, RG = 3k, VOUT = 1V RF = 3k, RG = 3k, VOUT = 10V VIN = 0V Pin 8 Current = 50µA q q q q q q q q q q q q q Non-Inverting Input Current Power Supply Rejection Inverting Input Current Power Supply Rejection AV ROL VOUT IOUT SR BW tr tPD ts IS Large Signal Voltage Gain Transresistance, ∆VOUT/∆IIN– Output Swing Output Current Slew Rate (Note 2, 3) Bandwidth Rise Time, Fall Time (Note 3) Propagation Delay Overshoot Settling Time, 0.1% Supply Current Supply Current, Shutdown The q denotes specifications which apply over the operating temperature range. Note 1: A heat sink may be required. 90 70 5 1.5 ± 12 ± 10 50 100 105 45 ± 13 100 500 10 30 25 5 280 40 q q q 1 350 2 1000 Note 2: Non-Inverting operation, VOUT = ±10V, measured at ±5V. Note 3: AC parameters are 100% tested on the plastic DIP packaged parts (N suffix), and are sample tested on every lot of the SO packaged parts (S suffix). 2 U nA/V dB nA/V nA/V dB dB MΩ MΩ V V mA V/µs MHz ns ns % ns mA µA W U U WW W LT1217 TYPICAL PERFOR A CE CHARACTERISTICS Voltage Gain and Phase vs Frequency, Gain = 6dB 8 7 6 PHASE 0 45 90 –3dB BANDWIDTH (MHz) VOLTAGE GAIN (dB) 5 4 3 2 1 0 –1 –2 0.01 GAIN –3dB BANDWIDTH (MHz) VS = ±15V RL = 100Ω RF = 3k 0.1 1.0 10 LT1217 • TPC01 FREQUENCY (MHz) Voltage Gain and Phase vs Frequency, Gain = 20dB 22 21 20 PHASE 0 45 90 –3dB BANDWIDTH (MHz) –3dB BANDWIDTH (MHz) VOLTAGE GAIN (dB) 19 18 17 16 15 14 13 12 0.01 GAIN VS = ±15V RL = 100Ω RF = 3k 0.1 1.0 10 LT1217 • TPC04 FREQUENCY (MHz) Voltage Gain and Phase vs Frequency, Gain = 40dB 42 41 40 VOLTAGE GAIN (dB) PHASE –3dB BANDWIDTH (MHz) 39 38 37 36 35 34 33 32 0.01 GAIN 135 180 225 RF = 250Ω 1.5 RF = 1k RF = 5.1k –3dB BANDWIDTH (MHz) VS = ±15V RL = 100Ω RF = 3k 0.1 1.0 10 LT1217 • TPC07 FREQUENCY (MHz) UW 30 25 –3dB Bandwidth vs Supply Voltage, Gain = 2, RL = 100Ω PEAKING ≤ 0.5dB PEAKING ≤ 5dB 30 25 20 15 10 –3dB Bandwidth vs Supply Voltage, Gain = 2, RL = 1kΩ PEAKING ≤ 0.5dB PEAKING ≤ 5dB RF = 1k RF = 2k RF = 3k RF = 5.1k PHASE SHIFT (DEGREES) PHASE SHIFT (DEGREES) 135 180 225 20 RF = 1k 15 10 5 0 0 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (±V) LT1217 • TPC02 RF = 2k RF = 3k RF = 5.1k 5 0 0 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (±V) LT1217 • TPC03 20 18 16 14 12 10 8 6 4 2 0 –3dB Bandwidth vs Supply Voltage, Gain = 10, RL = 100Ω PEAKING ≤ 0.5dB PEAKING ≤ 5dB RF = 750Ω RF = 1k RF = 2k RF = 3k RF = 5.1k 20 18 16 14 12 10 8 6 4 2 0 –3dB Bandwidth vs Supply Voltage, Gain = 10, RL = 1kΩ PEAKING ≤ 0.5dB PEAKING ≤ 5dB RF = 750Ω RF = 1k 135 180 225 RF = 2k RF = 3k RF = 5.1k 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (±V) LT1217 • TPC05 SUPPLY VOLTAGE (±V) LT1217 • TPC06 0 45 90 PHASE SHIFT (DEGREES) 2.5 –3dB Bandwidth vs Supply Voltage, Gain = 100, RL = 100Ω 2.5 –3dB Bandwidth vs Supply Voltage, Gain = 100, RL = 1kΩ RF = 1k 2.0 2.0 1.5 RF = 5.1k RF = 250Ω 1.0 1.0 0.5 0.5 0 0 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (±V) LT1217 • TPC08 0 0 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (±V) LT1217 • TPC09 3 LT1217 TYPICAL PERFOR A CE CHARACTERISTICS Maximum Capacitive Load vs Feedback Resistor 10000 0.1 TOTAL HARMONIC DISTORTION (%) CAPACITIVE LOAD (pF) AV = 2 RL = 1k PEAKING ≤ 5dB 1000 VS = ±5V VS = ±15V DISTORTION (dBc) 100 10 1 2 3 4 5 6 7 8 9 10 FEEDBACK RESISTOR (kΩ) LT1217 • TPC10 V+ –1.0 Input Common Mode Limit vs Temperature OUTPUT SATURATION VOLTAGE (V) –0.5 –1.0 –1.5 –2.0 2.0 1.5 1.0 0.5 V– –50 –25 0 25 50 75 100 125 RL = ∞ ±5V ≤ VS ≤ ±18V OUTPUT SHORT CIRCUIT CURRENT (mA) COMMON MODE RANGE (V) –2.0 –3.0 3.0 2.0 1.0 V– –50 –25 V+ = +5V TO +18V V– = –5V TO –18V 0 25 50 75 PACKAGE TEMPERATURE (°C) LT1217 • TPC13 Spot Noise Voltage and Current vs Frequency 100 POWER SUPPLY REJECTION (dB) SPOT NOISE (nV/√Hz OR pA/√Hz) en POSITIVE 40 30 20 10 0 0.01 VS = ±15V RL = 100Ω RF = RG =3k 0.1 NEGATIVE RESISTANCE (Ω) 10 in– 1 in+ 0.1 0.01 0.1 1 FREQUENCY (kHz) 10 4 UW 100 LT1217 • TPC16 Total Harmonic Distortion vs Frequency –20 VS = ±15V RL = 400Ω RF = RG = 3kΩ 2nd and 3rd Harmonic Distortion vs Frequency VS = ±15V RL = 100Ω VO = 2Vpp RF = 3k AV = 10dB 3RD –40 2ND –50 –30 0.01 VO = 7VRMS VO = 2VRMS 0.001 10 100 1000 FREQUENCY (Hz) LT1217 • TPC11 –60 10000 100000 0.1 1 FREQUENCY (MHz) 10 LT1217 • TPC12 V+ Output Saturation Voltage vs Temperature 120 110 100 90 80 70 60 50 Output Short Circuit Current vs Temperature 125 40 –50 –25 0 25 50 75 100 125 PACKAGE TEMPERATURE (°C) LT1217 • TPC14 PACKAGE TEMPERATURE (°C) LT1217 • TPC15 Power Supply Rejection vs Frequency 70 60 1000 50 100 10000 Output Impedance vs Frequency SHUTDOWN (PIN 8 AT GND) 10 1 NORMAL VS = ±15V RF = RG = 3k 0.1 1 10 LT1217 • TPC18 100 1 10 LT1217 • TPC17 0.1 0.01 FREQUENCY (MHz) FREQUENCY (MHz) LT1217 TYPICAL PERFOR A CE CHARACTERISTICS Settling Time to 10mV vs Output Step 10 8 6 VS = ±15V RF = RG = 3k INVERTING OUTPUT STEP (V) SUPPLY CURRENT (mA) OUTPUT STEP (V) 4 2 0 –2 –4 –6 –8 –10 0 50 100 150 200 250 300 SETTLING TIME (ns) LT1217 • TPC19 NON-INVERTING NON-INVERTING INVERTING APPLICATI S I FOR ATIO Current Feedback Basics The small signal bandwidth of the LT1217, like all current feedback amplifiers, isn’t a straight inverse function of the closed loop gain. This is because the feedback resistors determine the amount of current driving the amplifier’s internal compensation capacitor. In fact, the amplifier’s feedback resistor (RF) from output to inverting input works with internal junction capacitances of the LT1217 to set the closed loop bandwidth. Even though the gain set resistor (RG) from inverting input to ground works with RF to set the voltage gain just like it does in a voltage feedback op amp, the closed loop bandwidth does not change. This is because the equivalent gain bandwidth product of the current feedback amplifier is set by the Thevenin equivalent resistance at the inverting input and the internal compensation capacitor. By keeping RF constant and changing the gain with RG, the Thevenin resistance changes by the same amount as the change in gain. As a result, the net closed loop bandwidth of the LT1217 remains the same for various closed loop gains. The curve on the first page shows the LT1217 voltage gain versus frequency while driving 100Ω, for five gain settings from 1 to 100. The feedback resistor is a constant 3k and the gain resistor is varied from infinity to 30Ω. Second order effects reduce the bandwidth somewhat at the higher gain settings. U W UW Settling Time to 1mV vs Output Step 10 8 6 4 2 0 –2 –4 –6 –8 –10 0 100 200 300 400 500 SETTLING TIME (ns) LT1217 • TPC20 Supply Current vs Supply Voltage 1.4 1.2 1.0 0.8 T = –55°C 0.6 0.4 0.2 T = –55°C T = 25°C, 125°C SHUTDOWN PIN 8 AT GND 0 2 4 6 8 10 12 14 16 18 T = 125°C VS = ±15V RF = RG = 3k NON-INVERTING INVERTING T = 25°C NON-INVERTING INVERTING 0.0 SUPPLY VOLTAGE (±V) LT1217 • TPC21 U UO Feedback Resistor Selection The small signal bandwidth of the LT1217 is set by the external feedback resistors and the internal junction capacitors. As a result, the bandwidth is a function of the supply voltage, the value of the feedback resistor, the closed loop gain and load resistor. The characteristic curves of bandwidth versus supply voltage are done with a heavy load (100Ω) and a light load (1kΩ) to show the effect of loading. These graphs also show the family of curves that result from various values of the feedback resistor. These curves use a solid line when the response has less than 0.5dB of peaking and a dashed line when the response has 0.5dB to 5dB of peaking. The curves stop where the response has more than 5dB of peaking. At a gain of two, on ±15V supplies with a 3kΩ feedback resistor, the bandwidth into a light load is 13.5MHz with a little peaking, but into a heavy load the bandwidth is 10MHz with no peaking. At very high closed loop gains, the bandwidth is limited by the gain bandwidth product of about 100MHz. The curves show that the bandwidth at a closed loop gain of 100 is about 1MHz. Capacitance on the Inverting Input Current feedback amplifiers want resistive feedback from the output to the inverting input for stable operation. Take 5 LT1217 APPLICATI S I FOR ATIO care to minimize the stray capacitance between the output and the inverting input. Capacitance on the inverting input to ground will cause peaking in the frequency response (and overshoot in the transient response), but it does not degrade the stability of the amplifier. The amount of capacitance that is necessary to cause peaking is a function of the closed loop gain taken. The higher the gain, the more capacitance is required to cause peaking. We can add capacitance from the inverting input to ground to increase the bandwidth in high gain applications. For example, in this gain of 100 application, the bandwidth can be increased from 1MHz to 2MHz by adding a 2200pF capacitor. VIN + LT1217 VOUT – RF 3k CG RG 30Ω LT1229 • TA03 Boosting Bandwidth of High Gain Amplifier with Capacitance on Inverting Input 45 44 43 42 GAIN (dB) 41 40 39 38 37 36 35 100k 1M FREQUENCY (Hz) LT1217 • TA04 CG = 4700pF CG = 2200pF CG = 0 10M Capacitive Loads The LT1217 can be isolated from capacitive loads with a small resistor (10Ω to 20Ω) or it can drive the capacitive load directly if the feedback resistor is increased. Both techniques lower the amplifier’s bandwidth about the 6 U same amount. The advantage of resistive isolation is that the bandwidth is only reduced when the capacitive load is present. The disadvantage of resistor isolation is that resistive loading causes gain errors. Because the DC accuracy is not degraded with resistive loading, the desired way of driving capacitive loads, such as flash converters, is to increase the feedback resistor. The Maximum Capacitive Load versus Feedback Resistor curve shows the value of feedback resistor and capacitive load that gives 5dB of peaking. For less peaking, use a larger feedback resistor. Power Supplies The LT1217 may be operated with single or split supplies as low as ±4.5V (9V total) to as high as ±18V (36V total). It is not necessary to use equal value split supplies, however, the offset voltage will degrade about 350µV per volt of mismatch. The internal compensation capacitor decreases with increasing supply voltage. The –3dB Bandwidth versus Supply Voltage curves show how this affects the bandwidth for various feedback resistors. Generally, the bandwidth at ±5V supplies is about half the value it is at ±15V supplies for a given feedback resistor. The LT1217 is very stable even with minimal supply bypassing, however, the transient response will suffer if the supply rings. It is recommended for good slew rate and settling time that 4.7µF tantalum capacitors be placed within 0.5 inches of the supply pins. Input Range The non-inverting input of the LT1217 looks like a 100MΩ resistor in parallel with a 3pF capacitor until the common mode range is exceeded. The input impedance drops somewhat and the input current rises to about 10µA when the input comes too close to the supplies. Eventually, when the input exceeds the supply by one diode drop, the base collector junction of the input transistor forward biases and the input current rises dramatically. The input current should be limited to 10mA when exceeding the supplies. The amplifier will recover quickly when the input is returned to its normal common mode range unless the input was over 500mV beyond the supplies, then it will take an extra 100ns. W U UO LT1217 APPLICATI Offset Adjust Output offset voltage is equal to the input offset voltage times the gain plus the inverting input bias current times the feedback resistor. The LT1217 output offset voltage can be nulled by pulling approximately 30µA from pin 1 or 5. The easy way to do this is to use a 100kΩ pot between pin 1 and 5 with a 430kΩ resistor from the wiper to ground for 15V supply applications. Use a 110k resistor when operating on a 5V supply. Shutdown Pin 8 activates a shutdown control function. Pulling more than 50µA from pin 8 drops the supply current to less than 350µA, and puts the output into a high impedance state. The easy way to force shutdown is to ground pin 8, using an open collector (drain) logic stage. An internal resistor limits current, allowing direct interfacing with no additional parts. When pin 8 is open, the LT1217 operates normally. Slew Rate The slew rate of a current feedback amplifier is not independent of the amplifier gain configuration the way it is in a traditional op amp. This is because the input stage and the output stage both have slew rate limitations. Inverting amplifiers do not slew the input and are therefore limited only by the output stage. High gain, non-inverting amplifiers are similar. The input stage slew rate of the LT1217 is about 50V/µs before it becomes non-linear and is enhanced by the normally reverse biased emitters on the input transistors. The output slew rate depends on the size of the feedback resistors. The output slew rate is about 850V/µs with a 3k feedback resistor and drops proportionally for larger values. The photos show the LT1217 with a 20V peak-to-peak output swing for three different gain configurations. Settling Time The characteristic curves show that the LT1217 settles to within 10mV of final value in less than 300ns for any output step up to 10V. Settling to 1mV of final value takes less than 500ns. Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. S I FOR ATIO U Large Signal Response, AV = 2, R F = RG = 3k, Slew Rate 500V/µs Large Signal Response, AV = –2, R F = 3k, RG = 1.5k, Slew Rate 850V/µs Large Signal Response, AV = 10, R F = 3k, RG = 330Ω, Slew Rate 150V/µs W U UO 7 LT1217 SI PLIFIED SCHE ATIC 7 90k 5 BIAS 1 PACKAGE DESCRIPTIO N8 Package 8-Lead Plastic DIP TJ MAX 150°C θJA 100°C/W 0.300 – 0.320 (7.620 – 8.128) 0.065 (1.651) TYP 0.009 - 0.015 (0.229 - 0.381) +0.025 0.325 –0.015 +0.635 8.255 –0.381 ( S8 Package 8-Lead Plastic SOIC TJ MAX 150° C θJA 150°C/W 0°– 8° TYP 0.010 – 0.020 × 45° (0.254 – 0.508) 0.016 – 0.050 0.406 – 1.270 8 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977 U W 8 3 W 60k 2 6 BIAS 4 LT1217 • TA08 Dimensions in inches (millimeters) unless otherwise noted. 0.045 – 0.065 (1.143 – 1.651) 0.130 ± 0.005 (3.302 ± 0.127) 0.400 (10.160) MAX 8 7 6 5 ) 0.045 ± 0.015 (1.143 ± 0.381) 0.100 ± 0.010 (2.540 ± 0.254) 0.125 (3.175) MIN 0.020 (0.508) MIN 0.250 ± 0.010 (6.350 ± 0.254) 0.018 ± 0.003 (0.457 ± 0.076) 1 2 3 4 N8 1291 0.189 – 0.197 (4.801 – 5.004) 8 0.053 – 0.069 (1.346 – 1.753) 0.004 – 0.010 (0.102 – 0.254) 0.228 – 0.244 (5.791 – 6.198) 0.014 – 0.019 (0.356 – 0.483) 0.050 (1.270) BSC 1 2 3 4 0.150 – 0.157 (3.810 – 3.988) 7 6 5 0.008 – 0.010 (0.203 – 0.254) S8 1291 BA/GP 0192 10K REV 0 © LINEAR TECHNOLOGY CORPORATION 1992