MICROCIRCUIT DATA SHEET
MNLM7171AM-X-RH REV 0B0
Original Creation Date: 03/16/00
Last Update Date: 08/31/00
Last Major Revision Date: 03/16/00
VERY HIGH SPEED, HIGH OUTPUT CURRENT, VOLTAGE FEEDBACK
AMPLIFIER: ALSO AVAILABLE GUARANTEED TO 300K RAD(Si)
TESTED TO MIL-STD-883, METHOD 1019.5
General Description
The LM7171 is a high speed voltage feedback amplifier that has the slewing characteristic
of a current feedback amplifier; yet it can be used in all traditional voltage feedback
amplifier configurations. The LM7171 is stable for gains as low as + 2 or -1. It provides
a very high slew rate at 2000V/uS (Minimum) and a wide gain-bandwidth product of 170MHz
(Minimum) while consuming only 6.5mA of supply current. It is ideal for video and high
speed signal processing applications such as HDSL and pulse amplifiers. With 100mA output
current, the LM7171 can be used for video distribution, as a transformer driver, or as a
laser diode driver.
Operation on +15V power supplies allows for large signal swings and provides greater
dynamic range and signal-to-noise ratio. The LM7171 is ideal for ADC/DAC systems. In
addition, the LM7171 is specified for +5V operation for portable applications.
The LM7171 is built on National's advanced VIP(TM)III(Vertically integrated PNP)
complementary bipolar process.
Industry Part Number
LM7171AM
NS Part Numbers
LM7171AMJ-QML
LM7171AMJ-QMLV
LM7171AMJFQML
LM7171AMJFQMLV
LM7171AMW-QML
LM7171AMW-QMLV
LM7171AMWG-QML
LM7171AMWG-QMLV
LM7171AMWGFQML
LM7171AMWGFQMLV
Prime Die
LM7171
Controlling Document
See Features Section
Processing
MIL-STD-883, Method 5004
Subgrp Description
1
2
3
4
5
6
7
8A
8B
9
10
11
Static tests at
Static tests at
Static tests at
Dynamic tests at
Dynamic tests at
Dynamic tests at
Functional tests at
Functional tests at
Functional tests at
Switching tests at
Switching tests at
Switching tests at
Temp (
o
C)
+25
+125
-55
+25
+125
-55
+25
+125
-55
+25
+125
-55
Quality Conformance Inspection
MIL-STD-883, Method 5005
1
MNLM7171AM-X-RH REV 0B0
MICROCIRCUIT DATA SHEET
Features
(Typical)
- Easy to use Voltage Feedback Topology
- Very High Slew Rate
- Wide Unity-Gain Bandwidth
- -3dB Frequency @ Av = +2
- Low Supply Current
- High Open Loop Gain
- High Output Current
- Specified for +15V and +5V operation
CONTROLLING DOCUMENTS:
LM7171AMJ-QML
5962-9553601QPA
LM7171AMJ-QMLV
5962-9553601VPA
LM7171AMJFQML
5962F9553601QPA
LM7171AMJFQMLV
5962F9553601VPA
LM7171AMW-QML
5962-9553601QHA
LM7171AMW-QMLV
5962-9553601VHA
LM7171AMWG-QML
5962-9553601QXA
LM7171AMWG-QMLV
5962-9553601VXA
LM7171AMWGFQML
5962F9553601QXA
LM7171AMWGFQMLV
5962F9553601VXA
2400V/us
200Mhz
220 Mhz
6.5 mA
85 dB
100 mA
Applications
- HDSL and ADSL Drivers
- Multimedia Broadcast Systems
- Professional Video Cameras
- Video Amplifiers
- Copiers/Scanners/Fax
- HDTV Amplifiers
- Pulse Amplifiers and Peak Detectors
- CATV/Fiber Optics Signal Processing
APPLICATION NOTES:
PERFORMANCE DISCUSSION: The LM7171 is a very high speed, voltage feedback amplifier. It
consumes only 6.5mA supply current while providing a gain-bandwidth product of 170MHz
(Minimum) and a slew rate of 2000V/uS (Minumum). It also has other great features such as
low differential gain and phase and high output current.
The LM7171 is a true voltage feedback amplifier. Unlike current feedback amplifiers (CFAs)
with a low inverting input impedance and a high non-inverting input impedance, both inputs
of voltage feedback amplifiers (VFA's) have high impedance nodes. The low impedance
inverting input in CFA's and a feedback capacitor create an additional pole that will lead
to instability. As a result, CFA's cannot be used in traditional op amp circuits such as
photodiode amplifiers, I-to-V converters and integrators, where a feedback capacitor is
required.
CIRCUIT OPERATION: The class AB input stage in the LM7171 is fully symmetrical and has a
similar slewing characteristic to the current feedback amplifiers. In the LM7171
Simplified Schematic, (see AN00006) Q1 through Q4 form the equivalent of the current
feedback input buffer, RE the equivalent of the feedback resistor, and stage A buffers the
inverting input. The triple-buffered output stage isolates the gain stage from the load to
provide low output impedance.
2
MNLM7171AM-X-RH REV 0B0
MICROCIRCUIT DATA SHEET
Applications
(Continued)
SLEW RATE CHARACTERISTIC: The slew rate of LM7171 is determined by the current available
to charge and discharge an internal high impedance node capacitor. This current is the
differential input voltage divided by the total degeneration resistor RE. Therefore, the
slew rate is proportional to the input voltage level, and the higher slew rates are
achievable in the lower gain configurations. See the LM7171 Commercial Data Book for slew
rate Vs input voltage level curve.
When a very fast, large signal, pulse is applied to the input of an amplifier, some
overshoot or undershoot occurs. By placing an external resistor such as 1K Ohm in series
with the input of the LM7171, the bandwidth is reduced to help lower the overshoot.
SLEW RATE LIMITATION: If the amplifier's input signal has too large of an amplitude at too
high of a frequency, the amplifier is said to be slew rate limited; this can cause ringing
in time domain, and peaking in frequency domain, at the output of the amplifier.
In the Commercial Data Book "Typical Performance Characteristics" section, there are
several curves of Av = +2 and Av = +4 versus input power levels. For the Av = +4 curves,
no peaking is present and the LM7171 responds identically to the different input power
levels of 30 mV, 100 mV and 300mV.
For the Av = +2 curves, slight peaking occurs. This peaking at high frequency (>100MHz) is
caused by a large input signal at high enough frequency, that it exceeds the amplifier's
slew rate. The peaking in frequency response does not limit the pulse response in time
domain. The LM7171 is stable with noise gain of > +2.
LAYOUT CONSIDERATION: PRINTED CIRCUIT BOARDS AND HIGH SPEED OP AMPS: There are many things
to consider when designing PC boards for high speed op amps. Without proper caution, it is
very easy to have excessive ringing, oscillation, and other degraded AC performance in
high speed circuits. As a rule, the signal traces should be short and wide to provide low
inductance and low impedance paths. Any unused board space must be grounded to reduce
stray signal pickup. Critical components should also be grounded at a common point to
eliminate voltage drop. Sockets add capacitance to the board and can affect high frequency
performance. It is better to solder the amplifier directly into the PC board without using
any socket.
USING PROBES: Active (FET) probes are ideal for taking high frequency measurements because
they have wide bandwidth, high input impedance, and low input capacitance. However, the
probe ground leads provide a long ground loop that will produce errors in measurement.
Instead, the probes can be grounded directly by removing the ground leads and probe
jackets and using scope probe jacks.
COMPONENT SELECTION & FEEDBACK RESISTOR: It is important in high speed applications to
keep all component leads short. For discrete components, choose carbon composition-type
resistors and mica-type capacitors. Surface mount components are preferred over discrete
components for minimum inductive effect.
Large values of feedback resistors can couple with parasitic capacitance and cause
undesirable effects such as ringing or oscillation in high speed amplifiers. For LM7171, a
feedback resistor of 510 Ohms gives optimal performance.
COMPENSATION FOR INPUT CAPACITANCE: The combinations of an amplfier's input capacitance
with the gain setting resistors adds a pole that can cause peaking or oscillation. To
solve this problem, a feedback capacitor with a value Cf>(Rg X Cin)/Rf can be used to
cancel that pole. For LM7171, a feedback capacitor of 2pF is recommended. AN00003
illustrates the compensation circuit.
POWER SUPPLY BYPASSING: Bypassing the power supply is necessary to maintain low power
supply impedance across the frequency spectrum. Both positive and negative power supplies
should be bypassed individually by placing 0.01uF ceramic capacitors directly to the power
supply pins and 2.2uF tantalum capacitors close to the power supply pins. See AN00004.
TERMINATION: In high frequency applications, reflection occur if signals are not properly
terminated. Figure 3, in the Commercial Data Book, shows a properly terminated signal,
while Figure 4, in the Commercial Data Book, shows an improperly terminated signal.
To minimize reflection, coaxial cable with matching characteristic impedance to the signal
source should be used. The other end of the cable should be terminated with the same value
terminator or resistor. For the commonly used cables, RG59 has 75 Ohm characteristic
impedance, and RG58 has 50 Ohm characteristic impedance.
3
MNLM7171AM-X-RH REV 0B0
MICROCIRCUIT DATA SHEET
Applications
(Continued)
DRIVING CAPACITIVE LOADS: Amplifiers driving capactive loads can oscillate or have ringing
at the output. To eliminate oscillation or reduce ringing, an isolation resistor can be
placed as shown on AN00005. The combination of the isolation resistor and the load
capacitor forms a pole to increase stability by adding more phase margin to the overall
system. The desired performance depends upon the value of the isolation resistor; the
bigger the isolation resistor, the more damped the pulse response becomes. For LM7171, a
50 Ohm isolation resistor is recommended for initial evaluation. Figure 6, in the
Commercial Data Book, shows the LM7171 driving a 150pF load with the 50 Ohm isolation
resistor.
POWER DISSIPATION: The maximum power allowed to dissipate in a device is defined as: Pd =
[Tj(max) - TA]/ThetaJA, where Pd (is the power dissipation in a device), Tj(max) (is the
maximum junction temperature), TA (is the ambient temperature), ThetaJA (is the thermal
resistance of a particular package).
For example, for the LM7171 in a J-8 package, the maximum power dissipation at 25 C
ambient temperature is 730mW.
The total power dissipation in a device can be calculated as: Pd = Pq + Pl
Pq is the quiescent power dissipated in a device with no load connected at the output. Pl
is the power dissipated in the device with a load connected at the output; it is not the
power dissipated by the load.
Furthermore, Pq = supply current x total supply voltage with no load, Pl = output current
x (voltage difference between supply voltage and output voltage of the same side of supply
voltage).
For example, the total power dissipated by the LM7171 with Vs = <15V and output voltage of
10V into 1K Ohm is:
Pd
=
=
=
=
Pq + Pl
(6.5mA)x(30V)+(10mA)x(15V - 10V)
195mW + 50mW
245mW
4
MNLM7171AM-X-RH REV 0B0
MICROCIRCUIT DATA SHEET
(Absolute Maximum Ratings)
(Note 1)
Supply Voltage (V+ - V-)
36V
Differential Input Voltage
(Note 6)
+10V
Maximum Junction Temperature
150 C
Maximum Power Dissipation
(Note 2, 3)
730mW
Output Short Circuit to Ground
(Note 4)
Continuous
Operating Temperature Range
-55 C < Ta < +125 C
Thermal Resistance
(Note 7)
ThetaJA
8-Pin CERAMIC DIP
(Still Air)
(500LF/Min Air flow)
10-Pin CERPAK
(Still Air)
(500LF/Min Air flow)
10-Pin CERAMIC SOIC (Still Air)
(500LF/Min Air flow)
106
53
182
105
182
105
C/W
C/W
C/W
C/W
C/W
C/W
ThetaJC
(Note 3)
8-Pin CERAMIC DIP
10-Pin CERPAK
10-Pin CERAMIC SOIC
Package Weight
(Typical)
8-Pin CERAMIC DIP
10-Pin CERPAK
10-Pin CERAMIC SOIC
Storage Temperature Range
ESD Tolerance
(Note 5)
3 C/W
5 C/W
5 C/W
965mg
235mg
230mg
-65 C < Ta < +150 C
3000V
Note 1:
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.
Operating Ratings indicate conditions for which the device is functional, but do not
guarantee specific performance limits. For guaranteed specifications and test
conditions, see the Electrical Characteristics. The guaranteed specifications apply
only for the test conditions listed. Some performance characteristics may degrade
when the device is not operated under the listed test conditions.
The maximum power dissipation must be derated at elevated temperatures and is
dictated by Tjmax (maximum junction temperature), ThetaJA (package junction to
ambient thermal resistance), and TA (ambient temperature). The maximum allowable
power dissipation at any temperature is Pdmax = (Tjmax - TA)/ThetaJA or the number
given in the Absolute Maximum Ratings, whichever is lower.
Note 2:
5
