TPS40056_16 Datasheet, PDF (14/33 Pages) Texas Instruments – WIDE-INPUT SYNCHRONOUS, TRACKING BUCK CONTROLLER

TPS40056
SLVS612 − APRIL 2006
APPLICATION INFORMATION
PWM MODULATOR RELATIONSHIPS
MODULATOR GAIN
vs
SWITCHING FREQUENCY
ESR Zero, + 1
AMOD = VIN / VS
VS
VC
Resultant, − 1
D = VC / VS
LC Filter, − 2
Figure 5
100
1k
10 k
100 k
fSW − Switching Frequency − Hz
Figure 6
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.
C2
(optional)
R3
C1
R2
−1
C3
R1
VFB
7
VOUT
RBIAS
+
8 COMP
EA_REF
UDG−03099
Figure 7. Type III Compensation Configuration
0 dB
+1
−1
−90°
GAIN
180°
−270°
PHASE
Figure 8. Type III Compensation Gain and Phase
14
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