lm6311 National Semiconductor Corporation, lm6311 Datasheet - Page 11

• Manufacturer Part Number: lm6311
• Description: Low Noise High Speed Voltage Feedback Operational Amplifier
• Manufacturer: National Semiconductor Corporation

Application Information
GENERAL INFORMATION
The LM6311 is a high speed complementary bipolar amplifi-
er with good video performance The LM6311 can operate
on
The LM6311 is available in two package types DIPs for
through hole designs and SO-8 surface mount packages
Benefits of the LM6311
LOW NOISE
The low noise performance of the LM6311 (typically 2 3 nV
per root-hertz) makes the LM6311 a good choice for signal
recovery high gain amplifiers other low noise designs
BALANCED DIFFERENTIAL INPUTS
The relatively low offset currents and low offset voltage of
the LM6311 make it easy to design differential signal recov-
ery circuits The low offset currents and voltage feedback
design make it easy to use the LM6311 in conventional ac-
tive filter designs
Single supply operation can avoid the cost of split power
supplies and make it easier to use the LM6311 in single
supply digital systems The LM6311 provides high band-
width for
Using the LM6311
LIMITS AND PRECAUTIONS
Supply Voltage
The absolute maximum supply voltage which may be ap-
plied to the LM6311 is 12V Designers should not design for
more than 10V nominal and carefully check supply toler-
ances under all conditions so that the voltages do not ex-
ceed the maximum
Differential Input Voltage
Differential input voltage is the difference in voltage be-
tween the non-inverting (
(
voltage is
when there is no power supplied to the op amp
Very fast input pulses into high gain circuits may cause the
output to saturate leading to an overload recovery time in
the millisecond range This requires inputs which are faster
than those usually used in video systems and gain levels
which will push the output of the amplifier toward the limit of
its output swing
Layout and Power Supply Bypassing
Since the LM6311 is a high speed (over 50 MHz) device
good high speed circuit layout practices should be followed
This should include the use of ground planes adequate
power supply bypassing removing metal from around the
input pins to reduce capacitance and careful routing of the
output signal lines to keep them away from the input pins
The power supply pins should be bypassed on both the neg-
ative and positive supply inputs with capacitors placed close
to the pins Surface mount capacitors should be used for
best performance and should be placed as close to the
a
b
5V SINGLE SUPPLY OPERATION
) of the op amp The absolute maximum differential input
g
2 5V supplies or from a
a
g
5V single supply operation See Figure 1
10V across the inputs This limit also applies
a
) input and the inverting input
a
5V single supply
11
pins as possible It is generally advisable to use two capaci-
tors at each supply voltage pin A small surface mount ca-
pacitor with a value of around 0 01
ceramic type with good RF performance should be placed
closest to the pin A larger capacitor usually in the range of
1 0
larger capacitor should be a device with good RF character-
istics and low ESR (equivalent series resistance) for best
results Ceramic and tantalum capacitors generally work
well as the larger capacitor
It is very important to reduce capacitance at the input and
output pins The ground plane and any other planes (power
etc ) should be ‘‘opened up’’ or removed near the pins The
opening should extend to the middle of the nearest pins as
a minimum
The LM6311 is built on a high performance bipolar process
The transistors used in this process have bandwidths much
higher than the LM6311 itself These transistors have a po-
tential to oscillate or ring at 400 MHz to 1 GHz when used in
layouts where the components are more than
away from the op amp pins These oscillations may produce
apparent shifts in voltage offset or excess current consump-
tion
To avoid this keep the input and output resistors as close
as possible to their respective pins Spacing within
(3 mm) or less is recommended for best results
For best performance low inductance resistors such as
chip resistors are recommended The use of wirewound re-
sistors is strongly not recommended
DIP devices should use socket pins which are flush with the
board Conventional sockets have additional capacitance
and are not recommended Obviously the use of wire-
wrapped sockets or the ‘‘white plastic’’ push in prototype
boards is strongly not recommended
Notes for
Operation
The LM6311 provides good high speed performance at
plying the LM6311
INPUT VOLTAGE RANGE
Input voltage should be near the center of the V
supplies For 5V and ground the inputs should be between
1 75V and 3 25V Inputs beyond this range will limit the out-
put swing reduce the common mode rejection and power
supply rejection lower the bandwidth and tend to greatly
increase distortion
For
recommended See Figure 2
OUTPUT VOLTAGE SWING
Output voltage swing will depend on the load and on what
voltage (ground or 2 5V) is on the other side of the load At
room temperature (25 C) and
tied to 2 5V the LM6311 will swing from 1 0V to 4 0V
For a ground referenced load this output range will shift
about 400 mV– 500 mV towards ground See Figure 3 for
schematics of loads referenced to the center and to ground
a
5V however certain limitations should be observed in ap-
a
F to 4 7
5V designs using a reference voltage near
F should also be placed near the pin The
a
5V Single Supply
a
5V supply with a 1 k
F (10 nF) usually a
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inch 6 mm)
a
a
and V
2 5V is
load
b