Datasheet

-180
-156
-132
-108
-84
-60
PHASE (
o
)
100
1k 10k 100k 1M
FREQUENCY (Hz)
-40
-20
0
20
40
60
GAIN (dB)
100
1k 10k 100k 1M
FREQUENCY (Hz)
G
EA-ACTUAL
x OPG
H
EA
=
1 + G
EA-ACTUAL
+ OPG
Z
1
=
R
C2
+
1
sC
C3
R
C1
+ R
C2
1
sC
C3
+
R
C1
1
Z
F
=
sC
C1
x
10,000 +
1
sC
C2
10,000 +
1
sC
C1
1
sC
C2
+
F
EA ACTUAL
I
Z
G
Z
-
=
LM2745, LM2748
SNOSAL2E –APRIL 2005–REVISED APRIL 2013 www.ti.com
C
C3
= 2.7 nF±10%, R
C1
= 39.2 kΩ±1%
R
C2
= 2.55 kΩ±1%
The transfer function of the compensation block can be derived by considering the compensation components as
impedance blocks Z
F
and Z
I
around an inverting op-amp:
As with the generic equation, G
EA-ACTUAL
must be modified to take into account the limited bandwidth of the error
amplifier. The result is:
The total control loop transfer function H is equal to the power stage transfer function multiplied by the error
amplifier transfer function.
H = G
PS
x H
EA
The bandwidth and phase margin can be read graphically from Bode plots of H
EA
as shown in Figure 32.
Figure 32. Overall Loop Gain and Phase
24 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated
Product Folder Links: LM2745 LM2748