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LT1217 Low Power 10MHz Current Feedback Amplifier
FEATURES
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DESCRIPTIO
1mA Quiescent Current 50mA Output Current (Minimum) 10MHz Bandwidth 500V/s Slew Rate 280ns Settling Time to 0.1% Wide Supply Range, 5V to 15V 1mV Input Offset Voltage 100nA Input Bias Current 100M 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/s 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 350A. 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
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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)
75
50 40 30 20 10 0 -10 RG = 30 RG = 100 RG = 330 RG = 1.3k RG =
-
RF 3k 75 CABLE
VOUT RG 3k 75
R AV = 1 + F RG AT AMPLIFIER OUTPUT. 6dB LESS AT VOUT.
LT1217 * TA01
-20 100k
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VS = 15V RF = 3k RL = 100 1M 10M 100M
LT1217 * TA02
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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 ..................... 0C to 70C Storage Temperature Range ................. - 65C to 150C Junction Temperature........................................... 150C Lead Temperature (Soldering, 10 sec.)................. 300C
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 = 0C to 70C unless otherwise noted.
CONDITIONS VCM = 0V VCM = 0V VCM = 0V f = 1kHz, RF = 1k, RG = 10 f = 1kHz, RF = 1k, RG = 10 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 M 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 = 400, VOUT = 10V RLOAD = 2k, VOUT = 10V RLOAD = 400, VOUT = 10V RLOAD = 2k RLOAD = 200 RLOAD = 0 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 = 50A
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).
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nA/V dB nA/V nA/V dB dB M M V V mA V/s MHz ns ns % ns mA A
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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 = 100 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)
VOLTAGE GAIN (dB)
19 18 17 16 15 14 13 12 0.01
GAIN
-3dB BANDWIDTH (MHz)
VS = 15V RL = 100 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 = 250 1.5 RF = 1k RF = 5.1k
-3dB BANDWIDTH (MHz)
VS = 15V RL = 100 RF = 3k 0.1 1.0 10
LT1217 * TPC07
FREQUENCY (MHz)
UW
30 25
-3dB Bandwidth vs Supply Voltage, Gain = 2, RL = 100
PEAKING 0.5dB PEAKING 5dB
30 25 20 15 10
-3dB Bandwidth vs Supply Voltage, Gain = 2, RL = 1k
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 = 100
PEAKING 0.5dB PEAKING 5dB RF = 750 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 = 1k
PEAKING 0.5dB PEAKING 5dB RF = 750 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 = 100
2.5
-3dB Bandwidth vs Supply Voltage, Gain = 100, RL = 1k
RF = 1k
2.0
2.0
1.5 RF = 5.1k
RF = 250
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
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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 (k)
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 = 100 RF = RG =3k 0.1 NEGATIVE
RESISTANCE ()
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 = 400 RF = RG = 3k
2nd and 3rd Harmonic Distortion vs Frequency
VS = 15V RL = 100 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 100, for five gain settings from 1 to 100. The feedback resistor is a constant 3k and the gain resistor is varied from infinity to 30. Second order effects reduce the bandwidth somewhat at the higher gain settings.
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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 = -55C 0.6 0.4 0.2 T = -55C T = 25C, 125C SHUTDOWN PIN 8 AT GND 0 2 4 6 8 10 12 14 16 18 T = 125C
VS = 15V RF = RG = 3k NON-INVERTING INVERTING
T = 25C
NON-INVERTING
INVERTING 0.0
SUPPLY VOLTAGE (V)
LT1217 * TPC21
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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 (100) and a light load (1k) 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 3k 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
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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 30
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 (10 to 20) or it can drive the capacitive load directly if the feedback resistor is increased. Both techniques lower the amplifier's bandwidth about the
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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 350V 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 4.7F tantalum capacitors be placed within 0.5 inches of the supply pins. Input Range The non-inverting input of the LT1217 looks like a 100M 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 10A 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.
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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 30A from pin 1 or 5. The easy way to do this is to use a 100k pot between pin 1 and 5 with a 430k 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 50A from pin 8 drops the supply current to less than 350A, 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/s 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/s 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
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Large Signal Response, AV = 2, R F = RG = 3k, Slew Rate 500V/s Large Signal Response, AV = -2, R F = 3k, RG = 1.5k, Slew Rate 850V/s Large Signal Response, AV = 10, R F = 3k, RG = 330, Slew Rate 150V/s
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LT1217
SI PLIFIED SCHE ATIC
7 90k 5 BIAS 1
PACKAGE DESCRIPTIO
N8 Package 8-Lead Plastic DIP
TJ MAX 150C JA 100C/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 150C JA 150C/W
0- 8 TYP
0.010 - 0.020 x 45 (0.254 - 0.508)
0.016 - 0.050 0.406 - 1.270
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
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8 3
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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
(c) LINEAR TECHNOLOGY CORPORATION 1992

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