Datasheet

20 dB/decade
g
m,in
/C
m
g
m,out
/C
I
40 dB/decade
FREQUENCY (Hz)
GAIN
V
IN
R
1
R
2
C
1
V
OUT
+
-
I
SEL
+V
R
3
R
4
C
2
I/O PIN
MICROCONTROLLER
R
EXT
LPV531
www.ti.com SNOSAK5B –MARCH 2006–REVISED MARCH 2013
Figure 39. Inverting AC Coupled Application
PROGRAMMABLE POWER LEVELS AND THE EFFECTS OF STABILITY COMPENSATION METHODS
USING EXTERNAL COMPONENTS
In some op amp application circuits, external capacitors are used to improve the stability of the feedback loop
around the amplifier. When using the programmable power level feature of the LPV531 such stability
improvement methods may not work. This is related to the internal frequency compensation method applied
inside the LPV531.
Figure 40 shows the bode plot of the frequency response of the LPV531. The gain-bandwidth product is
determined by the transconductance of the input stage (g
m,in
) and the internal Miller compensation capacitor
(C
m
). The non-dominant pole is formed by the transconductance of the output stage (g
m,out
) and the load
capacitance connected to the output of the LPV531 (C
l
). The frequency response crosses the frequency axis with
a single-pole slope (20 dB/decade). This ensures the stability of feedback loops formed around the LPV531.
Figure 40. Bode Plot of the Frequency Response
When the load capacitance is increased, the pole at the output will shift to lower frequencies. Eventually, the
output pole will shift below the unity gain frequency. This will cause the frequency characteristic to move through
the 0 dB axis with a slope of 40 dB/decade and a feedback loop formed around the LPV531 may oscillate. The
LPV531 is internally compensated in such a manner that it will be stable for load capacitances up to 100 pF.
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