Datasheet
1
R
C2
=
2SxC
C3
x
f
P1
= 2.55 k:
1
R
C1
=
2SxC
C2
x
f
Z1
= 39.8 k:
1
C
C3
=
2S x 10,000
x
= 2.73 nF
1
f
Z2
-
1
f
P1
1
C
C2
=
A
EA
x 10,000
- C
C1
= 882 pF
f
Z1
C
C1
=
A
EA
x 10,000 x f
P2
= 27 pF
100
1k 10k 100k 1M
FREQUENCY (Hz)
-100
-70
-40
-10
20
50
PHASE (
o
)
100
1k 10k 100k 1M
FREQUENCY (Hz)
0
12
24
36
48
60
GAIN (dB)
LM2745, LM2748
www.ti.com
SNOSAL2E –APRIL 2005–REVISED APRIL 2013
Figure 31. Error Amp. Gain and Phase
In VM regulators, the top feedback resistor R
FB2
forms a part of the compensation. Setting R
FB2
to 10 kΩ±1%,
usually gives values for the other compensation resistors and capacitors that fall within a reasonable range.
(Capacitances > 1 pF, resistances <1 MΩ) C
C1
, C
C2
, C
C3
, R
C1
, and R
C2
are selected to provide the poles and
zeroes at the desired frequencies, using the following equations:
In practice, a good trade off between phase margin and bandwidth can be obtained by selecting the closest
±10% capacitor values above what are suggested for C
C1
and C
C2
, the closest ±10% capacitor value below the
suggestion for C
C3
, and the closest ±1% resistor values below the suggestions for R
C1
, R
C2
. Note that if the
suggested value for R
C2
is less than 100Ω, it should be replaced by a short circuit. Following this guideline, the
compensation components will be:
C
C1
= 27 pF±10%, C
C2
= 820 pF±10%
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