Datasheet


SLVS612 − APRIL 2006
14
www.ti.com
APPLICATION INFORMATION
Figure 5
V
C
PWM MODULATOR RELATIONSHIPS
V
S
D = V
C
/ V
S
MODULATOR GAIN
vs
SWITCHING FREQUENCY
Modulator Gain − dB
Figure 6
f
SW
− Switching Frequency − Hz
100 1 k 10 k 100 k
ESR Zero, + 1
LC Filter, − 2
A
MOD
= V
IN
/ V
S
Resultant, − 1
A Type III topology, shown in Figure 7, 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 8. 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.
R
BIAS
Figure 7. Type III Compensation Configuration
UDG−03099
+
R1
R3
C3
C1
R2
7
8
EA_REF
VOUT
COMP
VFB
C2
(optional)
Figure 8. Type III Compensation Gain and Phase
GAIN
180°
−90°
−270°
PHASE
+ 1
− 1
− 1
0 dB