Page 1
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 A
V
=
−1, 60 MHz at A
V
=
−10.
With a slew rate of2000V/µs,2ndharmonic 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 Coax cable driver
n Video amplifier
n Flash ADC buffer
n High frequency filter
n Scanner and Imaging systems
Typical Application
VIP™is a registered trademark of National Semiconductor Corporation.
DS011328-1
Cable Driver
DS011328-2
May 1998
LM6181 100 mA, 100 MHz Current Feedback Amplifier
© 1999 National Semiconductor Corporation DS011328 www.national.com
Page 2
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
±
18V
Differential Input Voltage
±
6V
Input Voltage
±
Supply Voltage
Inverting Input Current 15 mA
Soldering Information
Dual-In-Line Package (N)
Soldering (10 sec) 260˚C
Small Outline Package (M)
Vapor Phase (60 seconds) 215˚C
Infrared (15 seconds) 220˚C
Output Short Circuit (Note 7)
Storage Temperature Range −65˚C ≤ T
J
≤ +150˚C
Maximum Junction Temperature 150˚C
ESD Rating (Note 2)
±
3000V
Operating Ratings
Supply Voltage Range 7V to 32V
Junction Temperature Range (Note 3)
LM6181AM −55˚C ≤ T
J
≤ +125˚C
LM6181AI, LM6181I −40˚C ≤ T
J
≤ +85˚C
Thermal Resistance (θ
JA
, 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
±
15V DC Electrical Characteristics
The following specifications apply for Supply Voltage
=
±
15V, R
F
=
820Ω, and R
L
=
1kΩunless otherwise noted. Boldface
limits apply at the temperature extremes; all other limits T
J
=
25˚C.
Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units
Typical Limit Typical Limit Typical Limit
(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)
V
OS
Input Offset Voltage 2.0 3.0 2.0 3.0 3.5 5.0 mV
4.0 3.5 5.5 max
TC
V
OS
Input Offset Voltage Drift 5.0 5.0 5.0 µV/˚C
I
B
Inverting Input Bias Current 2.0 5.0 2.0 5.0 5.0 10 µA
max
12.0 12.0 17.0
Non-Inverting Input Bias Current 0.5 1.5 0.5 1.5 2.0 3.0
3.0 3.0 5.0
TC I
B
Inverting Input Bias Current Drift 30 30 30 nA/˚C
Non-Inverting Input Bias 10 10 10
Current Drift
I
B
Inverting Input Bias Current V
S
=
±
4.5V,±16V 0.3 0.5 0.3 0.5 0.3 0.75 µA/V
max
PSR Power Supply Rejection 3.0 3.0 4.5
Non-Inverting Input Bias Current V
S
=
±
4.5V,±16V 0.05 0.5 0.05 0.5 0.05 0.5
Power Supply Rejection 1.5 1.5 3.0
I
B
Inverting Input Bias Current −10V ≤ VCM≤ +10V 0.3 0.5 0.3 0.5 0.3 0.75
CMR Common Mode Rejection 0.75 0.75 1.0
Non-Inverting Input Bias Current −10V ≤ V
CM
≤ +10V 0.1 0.5 0.1 0.5 0.1 0.5
Common Mode Rejection 0.5 0.5 0.5
CMRR Common Mode Rejection Ratio −10V ≤ V
CM
≤ +10V 60 50 60 50 60 50 dB
50 50 50 min
PSRR Power Supply Rejection Ratio V
S
=
±
4.5V,±16V 80 70 80 70 80 70 dB
70 70 65 min
R
O
Output Resistance A
V
=
−1, f=300 kHz 0.2 0.2 0.2 Ω
R
IN
Non-Inverting Input Resistance 10 10 10 MΩ
min
V
O
Output Voltage Swing R
L
=
1kΩ 12 11 12 11 12 11 V
min
11 11 11
R
L
=
100Ω 11 10 11 10 11 10
7.5 8.0 8.0
I
SC
Output Short Circuit Current 130 100 130 100 130 100 mA
75 85 85 min
www.national.com 2
Page 3
±
15V DC Electrical Characteristics (Continued)
The following specifications apply for Supply Voltage
=
±
15V, R
F
=
820Ω, and R
L
=
1kΩunless otherwise noted. Boldface
limits apply at the temperature extremes; all other limits T
J
=
25˚C.
Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units
Typical Limit Typical Limit Typical Limit
(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)
Z
T
Transimpedance R
L
=
1kΩ 1.8 1.0 1.8 1.0 1.8 0.8
0.5 0.5 0.4 MΩ
R
L
=
100Ω 1.4 0.8 1.4 0.8 1.4 0.7 min
0.4 0.4 0.35
I
S
Supply Current No Load, V
O
=
0V 7.5 10 7.5 10 7.5 10 mA
10 10 10 max
V
CM
Input Common Mode V+− 1.7V V+− 1.7V V+− 1.7V V
Voltage Range V
−
+ 1.7V V−+ 1.7V V−+ 1.7V
±
15V AC Electrical Characteristics
The following specifications apply for Supply Voltage
=
±
15V, R
F
=
820Ω,R
L
=
1kΩunless otherwise noted. Boldface limits
apply at the temperature extremes; all other limits T
J
=
25˚C.
Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units
Typical Limit Typical Limit Typical Limit
(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)
BW Closed Loop Bandwidth A
V
=
+2 100 100 100 MHz
min
−3 dB A
V
=
+10 80 80 80
A
V
=
−1 100 80 100 80 100 80
A
V
=
−10 60 60 60
PBW Power Bandwidth A
V
=
−1, V
O
=
5V
PP
60 60 60
SR Slew Rate Overdriven 2000 2000 2000 V/µs
min
A
V
=
−1, V
O
=
±
10V, 1400 1000 1400 1000 1400 1000
R
L
=
150Ω (Note 6)
t
s
Settling Time (0.1%)A
V
=
−1, V
O
=
±
5V 50 50 50 ns
R
L
=
150Ω
t
r,tf
Rise and Fall Time V
O
=
1V
PP
555
t
p
Propagation Delay Time V
O
=
1V
PP
666
i
n(+)
Non-Inverting Input Noise f=1 kHz 3 3 3
Current Density
i
n(−)
Inverting Input Noise f=1 kHz 16 16 16
Current Density
e
n
Input Noise Voltage
Density
f=1 kHz 4 4 4
Second Harmonic Distortion 2 VPP, 10 MHz −50 −50 −50 dBc
Third Harmonic Distortion 2 V
PP
, 10 MHz −55 −55 −50
Differential Gain R
L
=
150Ω
A
V
=
+2 0.05 0.05 0.05
%
NTSC
Differential Phase R
L
=
150Ω
A
V
=
+2 0.04 0.04 0.04 Deg
NTSC
www.national.com3
Page 4
±
5V DC Electrical Characteristics
The following specifications apply for Supply Voltage
=
±
5V, R
F
=
820Ω, and R
L
=
1kΩunless otherwise noted. Boldface
limits apply at the temperature extremes; all other limits T
J
=
25˚C.
Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units
Typical Limit Typical Limit Typical Limit
(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)
V
OS
Input Offset Voltage 1.0 2.0 1.0 2.0 1.0 3.0 mV
3.0 2.5 3.5 max
TC
V
OS
Input Offset Voltage Drift 2.5 2.5 2.5 µV/˚C
I
B
Inverting Input 5.0 10 5.0 10 5.0 17.5 µA
max
Bias Current 22 22 27.0
Non-Inverting Input 0.25 1.5 0.25 1.5 0.25 3.0
Bias Current 1.5 1.5 5.0
TC I
B
Inverting Input Bias 50 50 50 nA/˚C
Current Drift
Non-Inverting Input 3.0 3.0 3.0
Bias Current Drift
I
B
Inverting Input Bias Current V
S
=
±
4.0V,±6.0V 0.3 0.5 0.3 0.5 0.3 1.0 µA/V
max
PSR Power Supply Rejection 0.5 0.5 1.0
Non-Inverting Input V
S
=
±
4.0V,±6.0V 0.05 0.5 0.05 0.5 0.05 0.5
Bias Current
Power Supply Rejection 0.5 0.5 0.5
I
B
Inverting Input Bias Current −2.5V ≤ VCM≤ +2.5V 0.3 0.5 0.3 0.5 0.3 1.0
CMR Common Mode Rejection 1.0 1.0 1.5
Non-Inverting Input −2.5V ≤ V
CM
≤ +2.5V 0.12 0.5 0.12 0.5 0.12 0.5
Bias Current
Common Mode Rejection 1.0 0.5 0.5
CMRR Common Mode −2.5V ≤ V
CM
≤ +2.5V 57 50 57 50 57 50 dB
min
Rejection Ratio 47 47 47
PSRR Power Supply V
S
=
±
4.0V,±6.0V 80 70 80 70 80 64
Rejection Ratio 70 70 64
R
O
Output Resistance A
V
=
−1, f=300 kHz 0.25 0.25 0.25 Ω
R
IN
Non-Inverting 8 8 8 MΩ
Input Resistance min
V
O
Output Voltage Swing R
L
=
1kΩ 2.6 2.25 2.6 2.25 2.6 2.25 V
min
2.2 2.25 2.25
R
L
=
100Ω 2.2 2.0 2.2 2.0 2.2 2.0
2.0 2.0 2.0
I
SC
Output Short 100 75 100 75 100 75 mA
Circuit Current 70 70 70 min
Z
T
Transimpedance R
L
=
1kΩ 1.4 0.75 1.4 0.75 1.0 0.6
0.35 0.4 0.3 MΩ
R
L
=
100Ω 1.0 0.5 1.0 0.5 1.0 0.4 min
0.25 0.25 0.2
I
S
Supply Current No Load, V
O
=
0V 6.5 8.5 6.5 8.5 6.5 8.5 mA
8.5 8.5 8.5 max
V
CM
Input Common Mode V+− 1.7V V+− 1.7V V+− 1.7V V
Voltage Range V
−
+ 1.7V V−+ 1.7V V−+ 1.7V
www.national.com 4
Page 5
±
5V AC Electrical Characteristics
The following specifications apply for Supply Voltage
=
±
5V, R
F
=
820Ω, and R
L
=
1kΩunless otherwise noted. Boldface
limits apply at the temperature extremes; all other limits T
J
=
25˚C.
Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units
Typical Limit Typical Limit Typical Limit
(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)
BW Closed Loop Bandwidth −3 dB A
V
=
+2 50 50 50 MHz
min
A
V
=
+10 40 40 40
A
V
=
−1 55 35 55 35 55 35
A
V
=
−10 35 35 35
PBW Power Bandwidth A
V
=
−1, V
O
=
4V
PP
40 40 40
SR Slew Rate A
V
=
−1, V
O
=
±
2V, 500 375 500 375 500 375 V/µs
R
L
=
150Ω (Note 6) min
t
s
Settling Time (0.1%)A
V
=
−1, V
O
=
±
2V 50 50 50 ns
R
L
=
150Ω
t
r,tf
Rise and Fall Time V
O
=
1V
PP
8.5 8.5 8.5
t
p
Propagation Delay Time V
O
=
1V
PP
888
i
n(+)
Non-Inverting Input Noise f=1 kHz 3 3 3
Current Density
i
n(−)
Inverting Input Noise f=1 kHz 16 16 16
Current Density
e
n
Input Noise Voltage
Density
f=1 kHz 4 4 4
Second Harmonic Distortion 2 VPP, 10 MHz −45 −45 −45 dBc
Third Harmonic Distortion 2 V
PP
, 10 MHz −55 −55 −55
Differential Gain R
L
=
150Ω
A
V
=
+2 0.063 0.063 0.063
%
NTSC
Differential Phase R
L
=
150Ω
A
V
=
+2 0.16 0.16 0.16 Deg
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 in
2
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: Continuousshort circuit operation at elevated ambient temperature can result in exceeding the maximum allowed junction temperature of 150˚C. Output cur-
rents in excess of
±
130 mA over a long term basis may adversely affect reliability.
Note 8: For guaranteed Military Temperature Range parameters see RETS6181X.
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Page 6
Typical Performance Characteristics T
A
=
25˚C unless otherwise noted
CLOSED-LOOP
FREQUENCY RESPONSE
V
S
=
±
15V; R
f
=
820Ω;
R
L
=
1kΩ
DS011328-34
CLOSED-LOOP
FREQUENCY RESPONSE
V
S
=
±
15V; R
f
=
820Ω;
R
L
=
150Ω
DS011328-35
UNITY GAIN
FREQUENCY RESPONSE
V
S
=
±
15V; A
V
=
+1;
R
f
=
820Ω
DS011328-36
UNIT GAIN
FREQUENCY RESPONSE
V
S
=
±
5V; A
V
=
+1;
R
f
=
820Ω
DS011328-37
FREQUENCY RESPONSE
vs SUPPLY VOLTAGE
A
V
=
−1; R
f
=
820Ω;
R
L
=
1kΩ
DS011328-38
FREQUENCY RESPONSE
vs SUPPLY VOLTAGE
A
V
=
−1; R
f
=
820Ω;
R
L
=
150Ω
DS011328-39
INVERTING GAIN
FREQUENCY RESPONSE
V
S
=
±
15V; A
V
=
−1;
R
f
=
820Ω
DS011328-40
INVERTING GAIN
FREQUENCY RESPONSE
V
S
=
±
5V; A
V
=
−1;
R
f
=
820Ω
DS011328-41
NON-INVERTING GAIN
FREQUENCY RESPONSE
V
S
=
±
15V; A
V
=
+2;
R
f
=
820Ω
DS011328-42
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Page 7
Typical Performance Characteristics T
A
=
25˚C unless otherwise noted (Continued)
NON-INVERTING GAIN
FREQUENCY RESPONSE
V
S
=
±
5V; A
V
=
+2;
R
f
=
820Ω
DS011328-43
INVERTING GAIN
FREQUENCY RESPONSE
V
S
=
±
15V; A
V
=
−10;
R
f
=
820Ω
DS011328-44
INVERTING GAIN
FREQUENCY RESPONSE
V
S
=
±
5V; A
V
=
−10;
R
f
=
820Ω
DS011328-45
NON-INVERTING GAIN
FREQUENCY RESPONSE
V
S
=
±
15V; A
V
=
+10;
R
f
=
820Ω
DS011328-46
NON-INVERTING GAIN
FREQUENCY RESPONSE
V
S
=
±
5V; A
V
=
+10;
R
f
=
820Ω
DS011328-47
NON-INVERTING GAIN
FREQUENCY COMPENSATION
V
S
=
±
15V; A
V
=
+2;
R
L
=
150Ω
DS011328-48
BANDWIDTH vs Rf&R
S
A
V
=
−1, R
L
=
1kΩ
DS011328-49
OUTPUT SWING vs
R
LOAD
PULSED, V
S
=
±
15V,
I
IN
=
±
200 µA, V
IN+
=
0V
DS011328-50
TRANSIMPEDANCE
vs FREQUENCY
V
S
=
±
15V
R
L
=
1kΩ
DS011328-51
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Page 8
Typical Performance Characteristics T
A
=
25˚C unless otherwise noted (Continued)
TRANSIMPEDANCE
vs FREQUENCY
V
S
=
±
15V
R
L
=
100Ω
DS011328-52
TRANSIMPEDANCE
vs FREQUENCY
V
S
=
±
5V
R
L
=
1kΩ
DS011328-53
TRANSIMPEDANCE
vs FREQUENCY
V
S
=
±
5V
R
L
=
100Ω
DS011328-54
SETTLING RESPONSE
V
S
=
±
15V; R
L
=
150Ω;
V
O
=
±
5V; A
V
=
−1
DS011328-55
SETTLING RESPONSE
V
S
=
±
5V; R
L
=
150Ω;
V
O
=
±
2V; A
V
=
−1
DS011328-56
SUGGESTED Rfand RSfor C
L
A
V
=
−1;R
L
=
150Ω
DS011328-57
SUGGESTED R
f
and RSFOR C
L
A
V
=
−1
DS011328-58
SUGGESTED R
f
and RSFOR C
L
A
V
=
+2; R
L
=
150Ω
DS011328-59
SUGGESTED R
f
and RSFOR C
L
A
V
=
+2
DS011328-60
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Page 9
Typical Performance Characteristics T
A
=
25˚C unless otherwise noted (Continued)
OUTPUT IMPEDANCE
vs FREQ
V
S
=
±
15V; A
V
=
−1
R
f
=
820Ω
DS011328-61
OUTPUT IMPEDANCE
vs FREQ
V
S
=
±
5V; A
V
=
−1
R
f
=
820Ω
DS011328-62
PSRR (V
S
+
) vs FREQUENCY
DS011328-63
PSRR (V
S
−
) vs FREQUENCY
DS011328-64
CMRR vs FREQUENCY
DS011328-65
INPUT VOLTAGE NOISE
vs FREQUENCY
DS011328-66
INPUT CURRENT
NOISE vs FREQUENCY
DS011328-67
SLEW RATE vs
TEMPERATURE A
V
=
−1;
R
L
=
150Ω,V
S
=
±
15V
DS011328-68
SLEW RATE vs
TEMPERATURE A
V
=
−1;
R
L
=
150Ω,V
S
=
±
5V
DS011328-69
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Page 10
Typical Performance Characteristics T
A
=
25˚C unless otherwise noted (Continued)
−3 dB BANDWIDTH
vs TEMPERATURE
A
V
=
−1
DS011328-70
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+1
V
S
=
±
15V; R
L
=
1kΩ
DS011328-71
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+1
V
S
=
±
15V; R
L
=
100Ω
DS011328-72
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+1
V
S
=
±
5V; R
L
=
1kΩ
DS011328-73
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+1
V
S
=
±
5V; R
L
=
100Ω
DS011328-74
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
−1
V
S
=
±
15V; R
L
=
1kΩ
DS011328-75
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
−1
V
S
=
±
15V; R
L
=
100Ω
DS011328-76
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
−1
V
S
=
±
5V; R
L
=
1kΩ
DS011328-77
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
−1
V
S
=
±
5V; R
L
=
100Ω
DS011328-78
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Page 11
Typical Performance Characteristics T
A
=
25˚C unless otherwise noted (Continued)
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+2
V
S
=
±
15V; R
L
=
1kΩ
DS011328-79
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+2
V
S
=
±
15V; R
L
=
100Ω
DS011328-80
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+2
V
S
=
±
5V; R
L
=
1kΩ
DS011328-81
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+2
V
S
=
±
5V; R
L
=
100Ω
DS011328-82
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
−10
V
S
=
±
15V; R
L
=
1kΩ
DS011328-83
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
−10
V
S
=
±
15V; R
L
=
100Ω
DS011328-84
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
−10
V
S
=
±
5V; R
L
=
1kΩ
DS011328-85
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
−10
V
S
=
±
5V; R
L
=
100Ω
DS011328-86
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+10
V
S
=
±
15V; R
L
=
1kΩ
DS011328-87
www.national.com11
Page 12
Typical Performance Characteristics T
A
=
25˚C unless otherwise noted (Continued)
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+10
V
S
=
±
15V; R
L
=
100Ω
DS011328-88
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+10
V
S
=
±
5V; R
L
=
1kΩ
DS011328-89
SMALL SIGNAL PULSE
RESPONSE vs TEMP,
A
V
=
+10
V
S
=
±
5V; R
L
=
100Ω
DS011328-90
OFFSET VOLTAGE
vs TEMPERATURE
DS011328-91
OFFSET VOLTAGE
vs TEMPERATURE
DS011328-92
TRANSIMPEDANCE
vs TEMPERATURE
DS011328-93
TRANSIMPEDANCE vs
TEMPERATURE
DS011328-94
QUIESCENT CURRENT
vs TEMPERATURE
DS011328-95
PSRR vs TEMPERATURE
DS011328-96
www.national.com 12
Page 13
Typical Performance Characteristics T
A
=
25˚C unless otherwise noted (Continued)
CMRR vs TEMPERATURE
DS011328-97
NON-INVERTING BIAS
CURRENT vs TEMPERATURE
DS011328-98
INVERTING BIAS
CURRENT vs TEMPERATURE
DS011328-99
PSR I
B(+)
vs TEMPERATURE
DS011328-A0
PSR I
B(−)
vs TEMPERATURE
DS011328-A1
CMR I
B(+)
vs TEMPERATURE
DS011328-A2
CMR I
B(−)
vs TEMPERATURE
DS011328-A3
I
SC(+)
vs TEMPERATURE
DS011328-A6
I
SC(−)
vs TEMPERATURE
DS011328-A4
www.national.com13
Page 14
Typical Performance Characteristics
Absolute Maximum Power Derating Curves
DS011328-30
N-Package
DS011328-31
*
θ
JA
=
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
Page 15
Typical Performance Characteristics (Continued)
Simplified Schematic
DS011328-32
www.national.com15
Page 16
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.
The closed-loop bandwidth of the LM6181 depends on the
feedback resistance, R
f
. Therefore, RSand not Rf, must be
varied to adjust for the desired closed-loop gain as in
Figure
2
.
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: R
f
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 R
f
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 R
f
typical 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 Rfto 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
DS011328-14
FIGURE 2. RSIs Adjusted to Obtain
the Desired Closed Loop Gain, A
VCL
www.national.com 16
Page 17
Typical Applications (Continued)
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.
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 R
f
and Rsfor
C
L
), or resistive isolation can be used (10Ω–51Ω typically
works well). Either technique, however, results in lowering
the system bandwidth.
Figure 6
illustrates the improvement obtained with using a
47Ω isolation resistor.
DS011328-15
3a: R
f
=
820Ω
DS011328-16
3b: R
f
=
1640Ω
FIGURE 3. Increasing Compensation
with Increasing R
f
DS011328-17
FIGURE 4. Reducing Rffor Large
Closed Loop Gains, R
f
=
500Ω
DS011328-18
5a
DS011328-19
5b
FIGURE 5. A
V
=
−1, LM6181 Can Directly
Drive 50 pF of Load Capacitance with 70 ns
of Ringing Resulting in Pulse Response
www.national.com17
Page 18
Typical Applications (Continued)
CAPACITIVE FEEDBACK
For voltage feedback amplifiers it is quite common to place a
small lead compensation capacitor in parallel with feedback
resistance, R
f
. 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 R
f
.
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
.
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
re-
spectively.
The open-loop circuit of
Figure 8
generates an overdrive re-
sponse by allowing the
±
0.5V input to exceed the linear input range of the amplifier.Typicalpositive and negative overdrive recovery times shown in
Figure 9
are 5 ns and 25 ns,
respectively.
DS011328-20
6a
DS011328-21
6b
FIGURE 6. Resistive Isolation of C
L
Provides Higher Fidelity Pulse Response. R
f
and RSCould Be Increased to Maintain A
V
=
−1
and Improve Pulse Response Characteristics.
DS011328-22
7a
DS011328-23
7b
FIGURE 7. RC Limits Amplifier
Bandwidth to 50 MHz, Eliminating
Peaking in the Resulting Pulse Response
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Page 19
Typical Performance
Characteristics
(Continued)
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.
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.
DS011328-24
FIGURE 8.
DS011328-25
FIGURE 9. Open-Loop Overdrive Recovery Time of
5 ns, and 25 ns from Test Circuit in
Figure 8
DS011328-26
FIGURE 10.
DS011328-27
FIGURE 11. Closed-Loop Overdrive Recovery
Time of 30 ns from Exceeding Output
Voltage Range from Circuit in
Figure 10
DS011328-28
FIGURE 12. Exceptional Output
Recovery from an Input that
Exceeds the Common-Mode Range
www.national.com19
Page 20
Connection Diagrams (For Ordering Information See Back Page)
Ordering Information
Package Temperature Range NSC
Drawing
Military Industrial
−55˚C to +125˚C −40˚C to +85˚C
8-Pin LM6181AMN LM6181AIN N08E
Molded DIP LM6181IN
8-Pin Small Outline LM6181AIM-8 M08A
Molded Package LM6181IM-8
16-Pin LM6181AIM M16A
Small Outline LM6181IM
8-Pin LM6181AMJ/883 J08A
Ceramic DIP
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
16-Pin Small Outline Package (M)
DS011328-4
*Heat sinking pins (Note 3)
Order Number LM6181IM or LM6181AIM
See NS Package Number M16A
www.national.com 20
Page 21
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
www.national.com21
Page 22
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
Page 23
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.
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.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
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Email: europe.support@nsc.com
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Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
www.national.com
LM6181 100 mA, 100 MHz Current Feedback Amplifier
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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