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PDF LM6172AMWG-QML Data sheet ( Hoja de datos )
| Número de pieza | LM6172AMWG-QML | |
| Descripción | Dual High Speed/ Low Power/ Low Distortion/ Voltage Feedback Amplifiers | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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May 1999
LM6172
Dual High Speed, Low Power, Low Distortion, Voltage
Feedback Amplifiers
General Description
The LM6172 is a dual high speed voltage feedback amplifier.
It is unity-gain stable and provides excellent DC and AC per-
formance. With 100 MHz unity-gain bandwidth, 3000V/µs
slew rate and 50 mA of output current per channel, the
LM6172 offers high performance in dual amplifiers; yet it
only consumes 2.3 mA of supply current each channel.
The LM6172 operates on ±15V power supply for systems
requiring large voltage swings, such as ADSL, scanners and
ultrasound equipment. It is also specified at ±5V power sup-
ply for low voltage applications such as portable video sys-
tems.
The LM6172 is built with National’s advanced VIP™ III (Ver-
tically Integrated PNP) complementary bipolar process. See
the LM6171 datasheet for a single amplifier with these same
features.
Features
(Typical Unless Otherwise Noted)
n Easy to Use Voltage Feedback Topology
n High Slew Rate 3000V/µs
n Wide Unity-Gain Bandwidth 100 MHz
n Low Supply Current 2.3 mA/Channel
n High Output Current 50 mA/channel
n Specified for ±15V and ±5V Operation
Applications
n Scanner I-to-V Converters
n ADSL/HDSL Drivers
n Multimedia Broadcast Systems
n Video Amplifiers
n NTSC, PAL® and SECAM Systems
n ADC/DAC Buffers
n Pulse Amplifiers and Peak Detectors
LM6172 Driving Capacitive Load
Connection Diagram
DS012581-50
8-Pin DIP/SO
DS012581-44
Top View
DS012581-1
VIP™ is a trademark of National Semiconductor Corporation.
PAL® is a registered trademark of and used under license from Advanced Micro Devices, Inc.
© 1999 National Semiconductor Corporation DS012581
www.national.com
1 page  
±5V DC Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for TJ = 25˚C, V+ = +5V, V− = −5V, VCM = 0V, and RL = 1 kΩ. Boldface
limits apply at the temperature extremes
Symbol
Parameter
Conditions
Typ
(Note 5)
LM6172I
Limit
Units
(Note 5)
PSRR
Power Supply Rejection Ratio
VS = ±15V to ±5V
65 min
95 75 dB
70 min
AV Large Signal Voltage
Gain (Note 6)
RL = 1 kΩ
82 70 dB
65 min
RL = 100Ω
78 65 dB
60 min
VO Output Swing
RL = 1 kΩ
3.4 3.1
V
3 min
−3.3
−3.1
V
−3 max
RL = 100Ω
2.9 2.5
V
2.4 min
−2.7
−2.4
V
−2.3
max
Continuous Output Current
Sourcing, RL = 100Ω
29
25
mA
(Open Loop) (Note 7)
24 min
Sinking, RL = 100Ω
−27 −24
mA
−23 max
ISC Output Short Circuit
Current
Sourcing
Sinking
93
−72
mA
mA
IS Supply Current
Both Amplifiers
4.4 6 mA
7 max
±5V AC Electrical Characteristics
Unless otherwise specified, TJ = 25˚C, V+ = +5V, V− = −5V, VCM = 0V, and RL = 1 kΩ.
Symbol
Parameter
Conditions
SR Slew Rate
Unity-Gain Bandwidth
−3 dB Frequency
φm Phase Margin
ts Settling Time (0.1%)
AD Differential Gain (Note 8)
φD Differential Phase (Note 8)
en Input-Referred
Voltage Noise
in Input-Referred
Current Noise
Second Harmonic
Distortion (Note 10)
Third Harmonic
AV = +2, VIN = 3.5 VPP
AV = +1
AV = +2
AV = −1, VOUT = ±1V,
RL = 500Ω
f = 1 kHz
f = 1 kHz
f = 10 kHz
f = 5 MHz
f = 10 kHz
LM61722
Typ
(Note 5)
750
70
130
45
57
72
0.4
0.7
11
1
−110
−48
−105
Units
V/µs
MHz
MHz
MHz
Deg
ns
%
Deg
dB
dB
dB
5 www.national.com
5 Page 
1⁄2 LM6172 Simplified Schematic
Application Notes
LM6172 Performance Discussion
The LM6172 is a dual high-speed, low power, voltage feed-
back amplifier. It is unity-gain stable and offers outstanding
performance with only 2.3 mA of supply current per channel.
The combination of 100 MHz unity-gain bandwidth,
3000V/µs slew rate, 50 mA per channel output current and
other attractive features makes it easy to implement the
LM6172 in various applications. Quiescent power of the
LM6172 is 138 mW operating at ±15V supply and 46 mW at
±5V supply.
LM6172 Circuit Operation
The class AB input stage in LM6172 is fully symmetrical and
has a similar slewing characteristic to the current feedback
amplifiers. In the LM6172 Simplified Schematic, Q1 through
Q4 form the equivalent of the current feedback input buffer,
RE the equivalent of the feedback resistor, and stage A buff-
ers the inverting input. The triple-buffered output stage iso-
lates the gain stage from the load to provide low output im-
pedance.
LM6172 Slew Rate Characteristic
The slew rate of LM6172 is determined by the current avail-
able 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 configura-
tions.
When a very fast large signal pulse is applied to the input of
an amplifier, some overshoot or undershoot occurs. By plac-
ing an external series resistor such as 1 kΩ to the input of
LM6172, the slew rate is reduced to help lower the over-
shoot, which reduces settling time.
DS012581-55
Reducing Settling Time
The LM6172 has a very fast slew rate that causes overshoot
and undershoot. To reduce settling time on LM6172, a 1 kΩ
resistor can be placed in series with the input signal to de-
crease slew rate. A feedback capacitor can also be used to
reduce overshoot and undershoot. This feedback capacitor
serves as a zero to increase the stability of the amplifier cir-
cuit. A 2 pF feedback capacitor is recommended for initial
evaluation. When the LM6172 is configured as a buffer, a
feedback resistor of 1 kΩ must be added in parallel to the
feedback capacitor.
Another possible source of overshoot and undershoot
comes from capacitive load at the output. Please see the
section “Driving Capacitive Loads” for more detail.
Driving Capacitive Loads
Amplifiers driving capacitive loads can oscillate or have ring-
ing at the output. To eliminate oscillation or reduce ringing,
an isolation resistor can be placed as shown in Figure 1. The
combination of the isolation resistor and the load capacitor
forms a pole to increase stability by adding more phase mar-
gin to the overall system. The desired performance depends
on the value of the isolation resistor; the bigger the isolation
resistor, the more damped (slow) the pulse response be-
comes. For LM6172, a 50Ω isolation resistor is recom-
mended for initial evaluation.
11 www.national.com
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