Datasheet

C =
1
2SfR
C
f
P
= = 240 kHz
1
2SR
C
C
R
P
+ R
1
//R
F
= 2 R
C
= (1 + )(1 + )
f = ñ
F
R
F
R
P
+ R
1
//R
F
R
1
R
C
1
= 6 V/V
LMP7707, LMP7708, LMP7709
www.ti.com SNOSAW5B –JUNE 2007–REVISED MARCH 2013
This method uses bode plot approximation. Some fine-tuning may be needed to get the best results.
Calculations:
As described in Step 1, use Equation 17:
(18)
Now substitute R
F
/R
1
= 1 into the equation above since this is a unity gain, inverting amplifier, then
(19)
According to Step 2 use Equation 14:
(20)
which leads to:
(21)
Choose a value of R
F
that is below 2 kΩ, in order to minimize the possibility of shunt capacitance across high
value resistors producing a negative effect on high frequency operation. If R
F
= R
1
= 1 kΩ, then R
F
// R
1
= 500 Ω.
For simplicity, choose R
P
= 0 Ω . The value of R
C
is derived from Equation 19 and has a value of R
C
= 250 Ω.
This is not a standard value. A value of R
C
= 330 Ω is a first choice (using 10% tolerance components).
The value of capacitor C is 2.2 nF. This value is significantly higher than the parasitic capacitances associated
with passive components and board layout, and is therefore a good solution.
Bench results:
For bench evaluation the LMP7707 in an inverting configuration has been verified under three different
conditions:
• Uncompensated
• Lead-lag compensation resulting in a phase margin of 45°
• Lead lag overcompensation resulting in a phase margin larger than 45°
The calculated components for these three conditions are
Condition R
C
C
Uncompensated NA NA
Compensated 330 Ω 2.2 nF
Overcompensated 240 Ω 3.3 nF
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