Datasheet

LMH6715
SNOSA10C –MAY 2002–REVISED APRIL 2013 www.ti.com
Frequency Response vs. R
F
Figure 29.
Figure 29 shows the LMH6715's frequency response as R
F
is varied (R
L
= 100Ω, A
V
= +2). This plot shows that
an R
F
of 200Ω results in peaking and marginal stability. An R
F
of 300Ω gives near maximal bandwidth and gain
flatness with good stability, but with very light loads (R
L
> 300Ω) the device may show some peaking. An R
F
of
500Ω gives excellent stability with good bandwidth and is the recommended value for most applications. Since all
applications are slightly different it is worth some experimentation to find the optimal R
F
for a given circuit. For
more information see Application Note OA-13 (Literature Number SNOA366) which describes the relationship
between R
F
and closed-loop frequency response for current feedback operational amplifiers.
When configuring the LMH6715 for gains other than +2V/V, it is usually necessary to adjust the value of the
feedback resistor. The two plots labeled shown in Figure 30 and Figure 31 provide recommended feedback
resistor values for a number of gain selections.
R
F
vs. Non-Inverting Gain
Figure 30.
Both plots show the value of R
F
approaching a minimum value (dashed line) at high gains. Reducing the
feedback resistor below this value will result in instability and possibly oscillation. The recommended value of R
F
is depicted by the solid line, which begins to increase at higher gains. The reason that a higher R
F
is required at
higher gains is the need to keep R
G
from decreasing too far below the output impedance of the input buffer. For
the LMH6715 the output resistance of the input buffer is approximately 160Ω and 50Ω is a practical lower limit for
R
G
. Due to the limitations on R
G
the LMH6715 begins to operate in a gain bandwidth limited fashion for gains of
±5V/V or greater.
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