TPS40200-Q1
SLUS739D –SEPTEMBER 2006–REVISED JULY 2011
www.ti.com
VOUT
AVOL
R10 R10
(S) =
Where:
V
IN
1+
+
R8 ZFS
´(1+ AVOL )
ZFS is the parallel combination of C7 in parallel with
the sum of R8 and the impedance of C8
AVOL is the open-loop gain of the error amplifier at
35 kHz, which is 44.6 or 33 dB
Figure 44 shows the result of the compensation. The crossover frequency is 35 kHz, and the phase margin is
45°. The response of the system is dominated by the ESR of the output capacitor and is exploited to produce an
essentially single-pole system with simple compensation.
50
180
160
140
120
100
80
40
30
20
Gain
10
0
Phase
-10
-20
-30
-40
-50
60
40
20
0
0.1
1
10
100
1000
Crossover Frequency - kHz
Figure 44. Overall System Gain and Phase Response
Figure 44 also shows the phase boost that gives the system a crossover phase margin of 47°.
The bill of materials for this application is shown in Table 3. Gerber PCB layout files and additional application
information are available from the factory.
30
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