LT1217 Low Power 10MHz Current Feedback Amplifier U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ 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. UO APPLICATI ■ ■ ■ ■ Video Amplifiers Buffers IF and RF Amplification Cable Drivers 8, 10, 12-Bit Data Acquisition Systems The LT1217 comes in the industry standard pinout and can upgrade the performance of many older products. UO ■ S TYPICAL APPLICATI Cable Driver Voltage Gain vs Frequency 60 – RF 3k 75Ω CABLE VOUT RG 3k VS = ±15V RF = 3k RL = 100Ω 50 75Ω LT1217 75Ω AMPLIFIER VOLTAGE GAIN (dB) + VIN 40 30 20 10 0 RG = 30Ω RG = 100Ω RG = 330Ω RG = 1.3k RG = ∞ –10 –20 100k R AV = 1 + F RG AT AMPLIFIER OUTPUT. 6dB LESS AT VOUT. 1M 10M 100M FREQUENCY (Hz) LT1217 • TA02 LT1217 • TA01 1 LT1217 U W W W 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 ELECTRICAL CHARACTERISTICS U RATI GS W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW NULL 1 8 SHUTDOWN –IN 2 7 V+ +IN 3 6 OUT V– 4 5 NULL LT1217CN8 LT1217CS8 S8 PART MARKING N8 PACKAGE S8 PACKAGE 8-LEAD PLASTIC DIP 8-LEAD PLASTIC SOIC 1217 LT1217 • POI01 VS = ±15V, TA = 0°C to 70°C unless otherwise noted. SYMBOL PARAMETER CONDITIONS VOS Input Offset Voltage VCM = 0V ● ±1 ±3 mV IIN+ Non-Inverting Input Current VCM = 0V ● ±100 ±500 nA IIN– Inverting Input Current VCM = 0V ● ±100 ±500 nA en Input Noise Voltage Density f = 1kHz, RF = 1k, RG = 10Ω in Input Noise Current Density f = 1kHz, RF = 1k, RG = 10Ω RIN Input Resistance VIN = ±10V CIN Input Capacitance ● 20 TYP MAX UNITS 6.5 nV/√Hz 0.7 pA/√Hz 100 MΩ 1.5 pF ● ±10 ±12 V Common Mode Rejection Ratio VCM = ±10V ● 60 66 dB Inverting Input Current Common Mode Rejection VCM = ±10V ● Input Voltage Range CMRR MIN 5 20 nA/V Power Supply Rejection Ratio VS = ±4.5V to ±18V ● Non-Inverting Input Current Power Supply Rejection VS = ±4.5V to ±18V ● 2 20 nA/V Inverting Input Current Power Supply Rejection VS = ±4.5V to ±18V ● 10 50 nA/V AV Large Signal Voltage Gain RLOAD = 2k, VOUT = ±10V RLOAD = 400Ω, VOUT = ±10V ● ● 90 70 105 dB dB ROL Transresistance, ∆VOUT/∆IIN– RLOAD = 2k, VOUT = ±10V RLOAD = 400Ω, VOUT = ±10V ● ● 5 1.5 45 MΩ MΩ VOUT Output Swing RLOAD = 2k RLOAD = 200Ω ● ● ±12 ±10 ±13 V V PSRR 68 76 dB IOUT Output Current RLOAD = 0Ω ● 50 100 mA SR Slew Rate (Note 2, 3) RF = 3k, RG = 3k ● 100 500 V/µs BW Bandwidth RF = 3k, RG = 3k, VOUT = 100mV 10 MHz tr Rise Time, Fall Time (Note 3) RF = 3k, RG = 3k, VOUT = 1V tPD Propagation Delay RF = 3k, RG = 3k, VOUT = 1V 25 ns Overshoot RF = 3k, RG = 3k, VOUT = 1V 5 % ts Settling Time, 0.1% RF = 3k, RG = 3k, VOUT = 10V IS Supply Current VIN = 0V ● 1 2 mA Supply Current, Shutdown Pin 8 Current = 50µA ● 350 1000 µA The ● denotes specifications which apply over the operating temperature range. Note 1: A heat sink may be required. 2 ● 30 40 280 ns ns 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). LT1217 U W TYPICAL PERFOR A CE CHARACTERISTICS PHASE 45 4 180 3 225 2 1 VS = ±15V RL = 100Ω RF = 3k 0 –1 –2 0.01 –3dB BANDWIDTH (MHz) 135 PHASE SHIFT (DEGREES) GAIN 5 PEAKING ≤ 0.5dB PEAKING ≤ 5dB 25 90 6 RF = 1k 15 RF = 2k 10 RF = 3k 5 1.0 2 4 6 8 10 12 14 PHASE 45 180 18 225 17 16 15 VS = ±15V RL = 100Ω RF = 3k RF = 1k 8 RF = 2k 6 RF = 3k 4 RF = 1k RF = 2k 10 RF = 3k 8 6 RF = 5.1k 2 0 2 4 6 8 10 12 14 16 0 18 2 4 6 8 10 36 35 VS = ±15V RL = 100Ω RF = 3k 1.0 10 FREQUENCY (MHz) 2.5 2.0 RF = 250Ω 1.5 RF = 1k RF = 5.1k 1.0 0.5 16 18 –3dB Bandwidth vs Supply Voltage, Gain = 100, RL = 1kΩ 2.0 RF = 250Ω 1.5 RF = 5.1k 1.0 0.5 0 0 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (±V) LT1217 • TPC07 14 LT1217 • TPC06 –3dB Bandwidth vs Supply Voltage, Gain = 100, RL = 100Ω 0 0.1 12 SUPPLY VOLTAGE (±V) –3dB BANDWIDTH (MHz) 225 –3dB BANDWIDTH (MHz) VOLTAGE GAIN (dB) 180 PHASE SHIFT (DEGREES) 135 37 32 0.01 12 RF = 1k 90 38 33 RF = 750Ω 14 45 GAIN 18 PEAKING ≤ 0.5dB PEAKING ≤ 5dB LT1217 • TPC05 2.5 16 14 4 RF = 5.1k 0 0 40 12 –3dB Bandwidth vs Supply Voltage, Gain = 10, RL = 1kΩ SUPPLY VOLTAGE (±V) PHASE 10 18 RF = 750Ω 10 Voltage Gain and Phase vs Frequency, Gain = 40dB 34 20 12 10 42 8 LT1217 • TPC03 2 1.0 6 4 16 14 LT1217 • TPC04 39 2 SUPPLY VOLTAGE (±V) PEAKING ≤ 0.5dB PEAKING ≤ 5dB FREQUENCY (MHz) 41 0 0 0.1 RF = 5.1k 18 16 –3dB BANDWIDTH (MHz) 135 PHASE SHIFT (DEGREES) GAIN 12 0.01 16 –3dB Bandwidth vs Supply Voltage, Gain = 10, RL = 100Ω 18 90 20 VOLTAGE GAIN (dB) 20 0 22 13 RF = 3k 10 LT1217 • TPC02 Voltage Gain and Phase vs Frequency, Gain = 20dB 14 RF = 2k 15 SUPPLY VOLTAGE (±V) LT1217 • TPC01 19 RF = 1k 20 0 0 10 PEAKING ≤ 0.5dB PEAKING ≤ 5dB 5 RF = 5.1k 0 0.1 –3dB Bandwidth vs Supply Voltage, Gain = 2, RL = 1kΩ 25 20 FREQUENCY (MHz) 21 30 –3dB BANDWIDTH (MHz) 7 VOLTAGE GAIN (dB) 30 0 8 –3dB Bandwidth vs Supply Voltage, Gain = 2, RL = 100Ω –3dB BANDWIDTH (MHz) Voltage Gain and Phase vs Frequency, Gain = 6dB 0 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (±V) LT1217 • TPC08 LT1217 • TPC09 3 LT1217 U W TYPICAL PERFOR A CE CHARACTERISTICS Maximum Capacitive Load vs Feedback Resistor Total Harmonic Distortion vs Frequency 1000 VS = ±5V VS = ±15V 100 VS = ±15V RL = 400Ω RF = RG = 3kΩ 0.01 VO = 7VRMS 2 3 5 4 6 8 7 9 1000 10000 Input Common Mode Limit vs Temperature OUTPUT SATURATION VOLTAGE (V) V+ COMMON MODE RANGE (V) –1.0 V+ = +5V TO +18V –3.0 3.0 V– = –5V TO –18V 1.0 V– –50 –25 0 25 50 75 100 –1.0 –1.5 RL = ∞ ±5V ≤ VS ≤ ±18V –2.0 2.0 1.5 1.0 0.5 0 25 75 50 70 60 50 in+ 100 FREQUENCY (kHz) 25 75 50 100 125 LT1217 • TPC15 Output Impedance vs Frequency 10000 60 1000 SHUTDOWN (PIN 8 AT GND) 50 POSITIVE 40 30 20 10 0 0.01 VS = ±15V RL = 100Ω RF = RG =3k 0.1 NEGATIVE 100 10 1 1 10 FREQUENCY (MHz) LT1217 • TPC16 0 PACKAGE TEMPERATURE (°C) RESISTANCE (Ω) 1 10 80 Power Supply Rejection vs Frequency POWER SUPPLY REJECTION (dB) en 1 90 40 –50 –25 125 70 0.1 100 LT1217 • TPC14 100 SPOT NOISE (nV/√Hz OR pA/√Hz) 100 110 PACKAGE TEMPERATURE (°C) Spot Noise Voltage and Current vs Frequency 4 Output Short Circuit Current vs Temperature –0.5 LT1217 • TPC13 0.1 0.01 LT1217 • TPC12 120 V– –50 –25 125 in– 10 FREQUENCY (MHz) Output Saturation Voltage vs Temperature PACKAGE TEMPERATURE (°C) 10 1 LT1217 • TPC11 LT1217 • TPC10 2.0 0.1 100000 FREQUENCY (Hz) FEEDBACK RESISTOR (kΩ) –2.0 2ND –60 100 10 10 OUTPUT SHORT CIRCUIT CURRENT (mA) 1 3RD –40 –50 VO = 2VRMS 0.001 10 VS = ±15V RL = 100Ω VO = 2Vpp RF = 3k AV = 10dB –30 DISTORTION (dBc) AV = 2 RL = 1k PEAKING ≤ 5dB TOTAL HARMONIC DISTORTION (%) CAPACITIVE LOAD (pF) –20 0.1 10000 V+ 2nd and 3rd Harmonic Distortion vs Frequency 0.1 0.01 NORMAL VS = ±15V RF = RG = 3k 0.1 1 10 FREQUENCY (MHz) LT1217 • TPC17 LT1217 • TPC18 LT1217 U W TYPICAL PERFOR A CE CHARACTERISTICS Settling Time to 10mV vs Output Step Settling Time to 1mV vs Output Step 10 VS = ±15V RF = RG = 3k 6 1.4 VS = ±15V RF = RG = 3k 8 6 INVERTING OUTPUT STEP (V) 4 2 NON-INVERTING 0 NON-INVERTING –2 T = 125°C 1.2 –4 –6 4 NON-INVERTING INVERTING 2 0 –2 NON-INVERTING –4 SUPPLY CURRENT (mA) 8 OUTPUT STEP (V) Supply Current vs Supply Voltage 10 1.0 T = 25°C 0.8 T = –55°C 0.6 T = –55°C T = 25°C, 125°C 0.4 –6 INVERTING –8 –10 INVERTING –10 0 50 100 200 150 250 0.0 100 0 300 SETTLING TIME (ns) 200 300 400 500 0 SETTLING TIME (ns) LT1217 • TPC19 2 6 4 8 10 12 14 16 18 SUPPLY VOLTAGE (±V) LT1217 • TPC20 LT1217 • TPC21 U W U UO APPLICATI SHUTDOWN PIN 8 AT GND 0.2 –8 S I FOR ATIO Current Feedback Basics Feedback Resistor Selection 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. 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. 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. 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 W U U UO 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 CG = 4700pF GAIN (dB) 42 41 40 37 CG = 0 1M 10M FREQUENCY (Hz) LT1217 • TA04 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 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 36 35 100k Power Supplies CG = 2200pF 39 38 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. 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. LT1217 U W U UO APPLICATI S I FOR ATIO Large Signal Response, AV = 2, R F = RG = 3k, Slew Rate 500V/µs 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. Large Signal Response, AV = –2, R F = 3k, RG = 1.5k, Slew Rate 850V/µs 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. Large Signal Response, AV = 10, R F = 3k, RG = 330Ω, Slew Rate 150V/µs 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. 7 LT1217 W W SI PLIFIED SCHE ATIC 7 90k 1 5 BIAS 60k 8 3 6 2 BIAS 4 LT1217 • TA08 U PACKAGE DESCRIPTIO 0.300 – 0.320 (7.620 – 8.128) N8 Package 8-Lead Plastic DIP TJ MAX θJA 150°C 100°C/W Dimensions in inches (millimeters) unless otherwise noted. 0.065 (1.651) TYP 0.045 – 0.065 (1.143 – 1.651) 0.130 ± 0.005 (3.302 ± 0.127) 8 0.009 - 0.015 (0.229 - 0.381) +0.025 0.325 –0.015 +0.635 8.255 –0.381 ( 0.125 (3.175) MIN 0.045 ± 0.015 (1.143 ± 0.381) ) 0.400 (10.160) MAX 0.100 ± 0.010 (2.540 ± 0.254) 7 6 5 0.250 ± 0.010 (6.350 ± 0.254) 0.020 (0.508) MIN 0.018 ± 0.003 (0.457 ± 0.076) 1 2 3 4 N8 1291 0.189 – 0.197 (4.801 – 5.004) S8 Package 8-Lead Plastic SOIC TJ MAX 150°C 0.010 – 0.020 × 45° (0.254 – 0.508) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 8 6 5 0.228 – 0.244 (5.791 – 6.198) 0.014 – 0.019 (0.356 – 0.483) 0.150 – 0.157 (3.810 – 3.988) 0.050 (1.270) BSC 1 Linear Technology Corporation 7 0.004 – 0.010 (0.102 – 0.254) 0.008 – 0.010 (0.203 – 0.254) θJA 150°C/W 8 0.053 – 0.069 (1.346 – 1.753) 2 3 4 S8 1291 BA/GP 0192 10K REV 0 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1992