Datasheet
1
2
ZERO
VCOMP VCOMP
f
R Cp
=
(108)
1
2
POLE
VCOMP VCOMP VCOMP _ P
VCOMP VCOMP _ P
f
R C C
C C
p
=
+
(109)
( )
1
1
VCOMP VCOMP
EA
VCOMP VCOMP VCOMP _ P
VCOMP VCOMP _ P
VCOMP VCOMP _ P
s( f )R C
G ( f ) gmv
R C C
C C s( f ) s( f )
C C
é ù
ê ú
ê ú
+
=
ê ú
é ù
æ ö
ê ú
+ +
ê ú
ç ÷
ê ú
ç ÷
+
ê ú
è ø
ë û
ë û
(110)
10
V
f Hz=
(111)
20
10 2
G ( f )
VLdB
V
PWM _ PS
VCOMP
V
f
gmv
f
C
fp
=
´
(112)
0 667
20
10
42
1 581
3 92
10 2 10
m
m
p
´
= =
´ ´ ´
. dB
VCOMP
Hz
S
. Hz
C . F
Hz
(113)
1
2
VCOMP
ZERO VCOMP
R
f Cp
=
(114)
1
30 51
2 1 581 3 3p m
= = W
´ ´ ´
VCOMP
R . k
. Hz . F
(115)
2 1
VCOMP
VCOMP _ P
POLE VCOMP VCOMP
C
C
f R Cp
=
-
(116)
3 3
0 258
2 20 33 2 3 3 1
m
m
p m
= =
´ ´ ´ W ´ -
VCOMP _ P
. F
C . F
Hz . k . F
(117)
UCC28019A
www.ti.com
.................................................................................................................................................. SLUS828B – DECEMBER 2008 – REVISED APRIL 2009
The voltage error amplifier is compensated with a zero, f
ZERO
, at the f
PWM_PS
pole and a pole, f
POLE
, placed at 20
Hz to reject high frequency noise and roll off the gain amplitude. The overall voltage loop crossover, f
V
, is desired
to be at 10 Hz. The compensation components of the voltage error amplifier are selected accordingly.
From Figure 31 , and the Design Calculator spreadsheet, the open loop gain of the voltage transfer function at 10
Hz is approximately 0.667 dB. Estimating that the parallel capacitor, C
VCOMP_P
, is much smaller than the series
capacitor, C
VCOMP
, the unity gain will be at f
V
, and the zero will be at f
PWM_PS
, the series compensation capacitor
is determined:
A 3.3- µ F capacitor is used for C
VCOMP
.
A 33.2-k Ω resistor is used for R
VCOMP
.
A 0.22- µ F capacitor is used for C
VCOMP_P
.
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