Datasheet

LMP7717, LMP7718
SNOSAY7H –MARCH 2007–REVISED MARCH 2013 www.ti.com
Figure 53. R
C
= 240Ω and C = 390 pF, Gain = −1
Figure 54. R
C
= 240Ω and C = 2.2 nF, Gain = −1
To summarize, the following steps were taken to compensate the LMP7717 for a gain of −1:
1. Values for R
c
and C were calculated from the Bode plot to give an expected phase margin of 45°. The values
were based on R
IN
= R
F
= 2 kΩ. These calculations gave R
c
= 330Ω and C = 390 pF.
2. To reduce the ringing C was increased to 2.2 nF which moved the pole of F, the feedback factor, farther
away from the A
VOL
curve.
3. There was still too much ringing so 2 dB of over-compensation was added to F. This was done by
decreasing R
C
to 240Ω.
The LMP7715 is the fully compensated part which is comparable to the LMP7717. Using the LMP7715 in the
same setup, but removing the compensation network, provided the response shown in Figure 55 .
Figure 55. LMP7715 Response
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