1 +

RF

Rc

¨

¨

©

§

= 18 dB = 7.9

LMP7717

RP

RC

C

RF

-

+

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. RP 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 RIN = ∞.

(11)

Using 2 k

Ω for RF and solving for RC gives RC = 2000/6.9 = 290Ω. The closest standard value for RC is 300Ω.

After some fine tuning in the lab RC = 330Ω and RP = 1.5 kΩ were chosen as the optimum values. RP 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 RC)

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 RP = RF = 0.

Figure 59. RC = 330Ω and C = 10 nF, Gain = +1

22

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