鈩?/div>
Slope =
鈭?0
dB / decade
ESR Zero
Figure 15. PWM and LC Filter Gain
The next step is to establish the required compensation gain to achieve the desired overall system response.
The target response is to have the crossover frequency between 1/10 to 1/4 times the switching frequency. To
have a phase margin greater than 45擄 and a gain margin greater than 6 dB.
A Type III compensation network, as shown in
Figure 16,
was used for this design. This network gives the best
overall flexibility for compensating the converter.
R
P1
C
PZ1
TPS40074
R
Z1
C
Z2
5
R
PZ2
6
COMP
FB
2
SAO
C
P2
R
SET2
R
SET1
UDG鈭?4126
Figure 16. Type III Conpensation with TPS40074
A typical bode plot to this type of compensation network is shown in
Figure 17.
28