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 ampli-
fiers. 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 cur-
rent 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
V
IN
Voltage Gain vs Frequency
+
LT1217
AMPLIFIER VOLTAGE GAIN (dB)
75Ω
50
40
30
20
10
0
–10
R
G
= 30Ω
R
G
= 100Ω
R
G
= 330Ω
R
G
= 1.3k
R
G
=
∞
–
R
F
3k
75Ω
CABLE
V
OUT
R
G
3k
75Ω
R
A
V
= 1 +
F
R
G
AT AMPLIFIER OUTPUT.
6dB LESS AT V
OUT
.
LT1217 • TA01
–20
100k
U
V
S
=
±15V
R
F
= 3k
R
L
= 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
V
OS
I
IN+
I
IN–
e
n
i
n
R
IN
C
IN
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
V
S
=
±15V,
T
A
= 0°C to 70°C unless otherwise noted.
CONDITIONS
V
CM
= 0V
V
CM
= 0V
V
CM
= 0V
f = 1kHz, R
F
= 1k, R
G
= 10Ω
f = 1kHz, R
F
= 1k, R
G
= 10Ω
V
IN
=
±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
V
CM
=
±10V
V
CM
=
±10V
V
S
=
±4.5V
to
±18V
V
S
=
±4.5V
to
±18V
V
S
=
±4.5V
to
±18V
R
LOAD
= 2k, V
OUT
=
±10V
R
LOAD
= 400Ω, V
OUT
=
±10V
R
LOAD
= 2k, V
OUT
=
±10V
R
LOAD
= 400Ω, V
OUT
=
±10V
R
LOAD
= 2k
R
LOAD
= 200Ω
R
LOAD
= 0Ω
R
F
= 3k, R
G
= 3k
R
F
= 3k, R
G
= 3k, V
OUT
= 100mV
R
F
= 3k, R
G
= 3k, V
OUT
= 1V
R
F
= 3k, R
G
= 3k, V
OUT
= 1V
R
F
= 3k, R
G
= 3k, V
OUT
= 1V
R
F
= 3k, R
G
= 3k, V
OUT
= 10V
V
IN
= 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
A
V
R
OL
V
OUT
I
OUT
SR
BW
t
r
t
PD
t
s
I
S
Large Signal Voltage Gain
Transresistance,
∆V
OUT
/∆I
IN–
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, V
OUT
=
±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
W W
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)
V
S
=
±15V
R
L
= 100Ω
R
F
= 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)
V
S
=
±15V
R
L
= 100Ω
R
F
= 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
R
F
= 250Ω
1.5
R
F
= 1k
R
F
= 5.1k
–3dB BANDWIDTH (MHz)
V
S
=
±15V
R
L
= 100Ω
R
F
= 3k
0.1
1.0
10
LT1217 • TPC07
FREQUENCY (MHz)
U W
30
25
–3dB Bandwidth vs Supply
Voltage, Gain = 2, R
L
= 100Ω
PEAKING
≤
0.5dB
PEAKING
≤
5dB
30
25
20
15
10
–3dB Bandwidth vs Supply
Voltage, Gain = 2, R
L
= 1kΩ
PEAKING
≤
0.5dB
PEAKING
≤
5dB
R
F
= 1k
R
F
= 2k
R
F
= 3k
R
F
= 5.1k
PHASE SHIFT (DEGREES)
PHASE SHIFT (DEGREES)
135
180
225
20
R
F
= 1k
15
10
5
0
0
2
4
6
8
10
12
14
16
18
SUPPLY VOLTAGE (±V)
LT1217 • TPC02
R
F
= 2k
R
F
= 3k
R
F
= 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, R
L
= 100Ω
PEAKING
≤
0.5dB
PEAKING
≤
5dB
R
F
= 750Ω
R
F
= 1k
R
F
= 2k
R
F
= 3k
R
F
= 5.1k
20
18
16
14
12
10
8
6
4
2
0
–3dB Bandwidth vs Supply
Voltage, Gain = 10, R
L
= 1kΩ
PEAKING
≤
0.5dB
PEAKING
≤
5dB
R
F
= 750Ω
R
F
= 1k
135
180
225
R
F
= 2k
R
F
= 3k
R
F
= 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, R
L
= 100Ω
2.5
–3dB Bandwidth vs Supply
Voltage, Gain = 100, R
L
= 1kΩ
R
F
= 1k
2.0
2.0
1.5
R
F
= 5.1k
R
F
= 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)
A
V
= 2
R
L
= 1k
PEAKING
≤
5dB
1000
V
S
=
±5V
V
S
=
±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
R
L
=
∞
±5V ≤
V
S
≤ ±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)
e
n
POSITIVE
40
30
20
10
0
0.01
V
S
=
±15V
R
L
= 100Ω
R
F
= R
G
=3k
0.1
NEGATIVE
RESISTANCE (Ω)
10
i
n–
1
i
n+
0.1
0.01
0.1
1
FREQUENCY (kHz)
10
4
U W
100
LT1217 • TPC16
Total Harmonic Distortion vs
Frequency
–20
V
S
=
±15V
R
L
= 400Ω
R
F
= R
G
= 3kΩ
2nd and 3rd Harmonic
Distortion vs Frequency
V
S
=
±15V
R
L
= 100Ω
V
O
= 2Vpp
R
F
= 3k
A
V
= 10dB
3RD
–40
2ND
–50
–30
0.01
V
O
= 7V
RMS
V
O
= 2V
RMS
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
V
S
=
±15V
R
F
= R
G
= 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
V
S
=
±15V
R
F
= R
G
= 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 (R
F
) 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 (R
G
) from inverting input
to ground works with R
F
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
R
F
constant and changing the gain with R
G
, 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
U W
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
V
S
=
±15V
R
F
= R
G
= 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 ca-
pacitors. 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
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