Datasheet
( )
( )
2
LC
MOD
MOD f
C
MOD f
f
1
A A and G
f A
æ ö
= ´ =
ç ÷
è ø
f
C
+
1
2p R1 C2 G
(Hertz)
( )
P2
1
f Hz
2 R3 C3
=
p ´ ´
( )
P1
1
f Hz
2 R2 C2
=
p ´ ´
( )
Z2
1
f Hz
2 R1 C3
=
p ´ ´
( )
Z1
1
f Hz
2 R2 C1
=
p ´ ´
+
R1
R
BIAS
R3
C3
C2
(optional)
C1
R2
7
8
VREF
V
O
COMP
VFB
UDG-08103
GAIN
180
°
-90
°
-270
°
PHASE
+1
-1
-1
0dB
TPS40054
TPS40055
TPS40057
www.ti.com
SLUS593H –DECEMBER 2003–REVISED JULY 2012
A Type III topology, shown in Figure 12, has two zero-pole pairs in addition to a pole at the origin. The gain and
phase boost of a Type III topology is shown in Figure 13. The two zeros are used to compensate the L-C
O
double pole and provide phase boost. The double pole is used to compensate for the ESR zero and provide
controlled gain roll-off. In many cases the second pole can be eliminated and the amplifier's gain roll-off used to
roll-off the overall gain at higher frequencies.
Figure 12. Type III Compensation Configuration Figure 13. Type III Compensation Gain and Phase
The poles and zeros for a Type III network are described in Equation 24 through Equation 27.
(24)
(25)
(26)
(27)
The value of R1 is somewhat arbitrary, but influences other component values. A value between 50 kΩ and
100 kΩ usually yields reasonable values.
The unity gain frequency is described in Equation 28.
where
• G is the reciprocal of the modulator gain at f
C
(28)
The modulator gain as a function of frequency at f
C
, is described in Equation 29.
(29)
Copyright © 2003–2012, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Link(s): TPS40054 TPS40055 TPS40057