Datasheet

= (1 + )(1 + )
f = ñ
F
R
F
R
P
+ R
1
//R
F
R
1
R
C
1
F
R
F
1
R
1
= 1 +
f = 0
f
Z
=
1
2í(R
C
+ R
1
//R
F
+ R
P
) C
f
P
=
1
2íR
C
C
= (1 + )( )
F
1 + s(R
C
+ R
1
//R
F
+ R
P
)C
R
1
1 + sR
C
C
R
F
1
-
R
1
R
C
C
R
F
+
R
P
LMP7707, LMP7708, LMP7709
www.ti.com SNOSAW5B –JUNE 2007–REVISED MARCH 2013
Figure 58. LMP7707 with Lead-Lag Compensation for Inverting Configuration
The inverse feedback factor of the circuit in Figure 58 is:
(13)
The pole of the inverse feedback function is located at:
(14)
The zero of the inverse feedback function is located at:
(15)
The low frequency inverse feedback factor is given by:
(16)
The high frequency inverse feedback factor is given by:
(17)
From these formulas, we can tell that
1. The 1/F's zero is located at a lower frequency compared to 1/F's pole.
2. The intersection point of 1/F and the open loop gain G is determined by the choice of resistor values for R
P
and R
C
if the values of R
1
and R
F
are set before compensation.
3. This procedure results in the creation of a pole-zero pair, the positions of which are interdependent.
4. This pole-zero pair is used to:
– Raise the 1/F value to a greater value in the region immediately to the left of its intercept with the A
function in order to meet the G
min
requirement.
– Achieve the preceding with no additional loop phase delay.
5. The location of the 1/F zero is determined by the following conditions:
– The value of 1/F at low frequency.
– The value of 1/F at the intersection point.
– The location of 1/F pole.
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