ncs2502 ON Semiconductor, ncs2502 Datasheet - Page 12

• Manufacturer Part Number: ncs2502
• Description: 650 Ua 110 Mhz Current Feedback Op Amp With Enable Feature
• Manufacturer: ON Semiconductor

General Design Considerations
performance video and data acquisition systems. For current
feedback architecture, its closed−loop bandwidth depends on
the value of the feedback resistor. The closed−loop bandwidth
is not a strong function of gain, as is for a voltage feedback
amplifier, as shown in Figure 27.
power supply voltages. By using lower power supplies, the
bandwidth is reduced, because the internal capacitance
increases. Smaller values of feedback resistor can be used at
lower supply voltages, to compensate for this affect.
Feedback and Gain Resistor Selection for Optimum
Frequency Response
is the ability to maintain optimum frequency response
independent of gain by using appropriate values for the
feedback resistor. To obtain a very flat gain response, the
feedback resistor tolerance should be considered as well.
Resistor tolerance of 1% should be used for optimum flatness.
Normally, lowering RF resistor from its recommended value
will peak the frequency response and extend the bandwidth
while increasing the value of RF resistor will cause the
frequency response to roll off faster. Reducing the value of RF
−10
−15
−20
10
−5
The current feedback amplifier is optimized for use in high
The −3.0 dB bandwidth is, to some extent, dependent on the
A current feedback operational amplifier’s key advantage
5
0
0.01
A
V
V
V
CC
EE
Figure 27. Frequency Response vs. R
= +2
= −5 V
= +5 V
0.1
1.0
FREQUENCY (MHz)
R
R
R
F
F
F
10
= 1 kW
= 1.2 kW
= 1.8 kW
100
1000
F
http://onsemi.com
10000
NCS2502
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resistor too far below its recommended value will cause
overshoot, ringing, and eventually oscillation.
experimentation to find the optimal RF for a given circuit. A
value of the feedback resistor that produces X0.1 dB of
peaking is the best compromise between stability and
maximal bandwidth. It is not recommended to use a current
feedback amplifier with the output shorted directly to the
inverting input.
Printed Circuit Board Layout Techniques
wideband amplifiers as the PCB parasitics can affect the
overall performance. Most important are stray capacitances at
the output and inverting input nodes as it can effect peaking
and bandwidth. A space (3/16″ is plenty) should be left around
the signal lines to minimize coupling. Also, signal lines
connecting the feedback and gain resistors should be short
enough so that their associated inductance does not cause high
frequency gain errors. Line lengths less than 1/4″ are
recommended.
Video Performance
NTSC, PAL, and HDTV video signals. Best performance is
obtained with back terminated loads as performance is
degraded as the load is increased. The back termination
reduces reflections from the transmission line and effectively
masks transmission line and other parasitic capacitances from
the amplifier output stage.
ESD Protection
(ESD) on all pins as specified in the attributes table. Note:
Human Body Model for +IN and −IN pins are rated at 0.8 kV
while all other pins are rated at 2.0 kV. Under closed−loop
operation, the ESD diodes have no effect on circuit
performance. However, under certain conditions the ESD
diodes will be evident. If the device is driven into a slewing
condition, the ESD diodes will clamp large differential
voltages until the feedback loop restores closed−loop
operation. Also, if the device is powered down and a large
input signal is applied, the ESD diodes will conduct.
Since each application is slightly different, it is worth some
Proper high speed PCB design rules should be used for all
This device designed to provide good performance with
This device is protected against electrostatic discharge