Datasheet

1 +
R
F
R
c
¨
¨
©
§
¨
¨
©
§
= 18 dB = 7.9
LMP7717
R
P
R
C
C
R
F
-
+
LMP7717, LMP7718
SNOSAY7H –MARCH 2007–REVISED MARCH 2013 www.ti.com
Figure 58. LMP7717 with Lead-Lag Compensation for Non-Inverting Configuration
Figure 58 is the result of using Equation 5 and additional experimentation in the lab. R
P
is not part of Equation 5,
but it is necessary to introduce another pole at the input stage for good performance at gain = +1. Equation 5 is
shown below with R
IN
= ∞.
(11)
Using 2 kΩ for R
F
and solving for R
C
gives R
C
= 2000/6.9 = 290Ω. The closest standard value for R
C
is 300Ω.
After some fine tuning in the lab R
C
= 330Ω and R
P
= 1.5 kΩ were chosen as the optimum values. R
P
together
with the input capacitance at the non-inverting pin inserts another pole into the compensation for the LMP7717.
Adding this pole and slightly reducing the compensation for 1/F (using a slightly higher resistor value for R
C
)
gives the optimum response for a gain of +1. Figure 59 is the response of the circuit shown in Figure 58.
Figure 60 shows the response of the LMP7715 in the buffer configuration with no compensation and R
P
= R
F
= 0.
Figure 59. R
C
= 330Ω and C = 10 nF, Gain = +1
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