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VREF
VIN
VOUT
Compensation
Network
+
_
Modulator
Filter
Current
Feedback
Network
+
_
V
C
Inductor-Capacitor (L-C) Selection
100 1 M1 k 100 k10 k
-90
0
45
135
180
-45
90
270
225
Duty Cycle %
Gain Phase
10
30
50
70
90
Phase - °
-20
20
40
80
100
0
60
Gain - dB
1 M1 k 100 k10 k
-90
0
45
135
180
-45
90
270
225
f - Frequency -Hz
Phase - °
100
-20
20
40
80
100
0
60
Gain - dB
Duty Cycle %
Gain Phase
10
30
50
70
90
TPS54283 , , TPS54286
SLUS749C – JULY 2007 – REVISED OCTOBER 2007
Figure 22. Small Signal Equivalent Block Diagram
The following figures plot the TPS5428x Output-to-Vc gain and phase versus frequency for various duty cycles
(10%, 30%, 50%, 70%, 90%) at three (200 mA, 400 mA, 600 mA) peak-to-peak ripple current levels. The loop
response curve selected to compensate the loop is based on the duty cycle of the application and the ripple
current in the inductor. Once the curve has been selected and the inductor value has been calculated, the output
capacitor is found by calculating the L-C resonant frequency required to compensate the feedback loop. A brief
example follows the curves.
Note that the internal error amplifier compensation is optimized for output capacitors with an ESR zero frequency
between 20kHz and 60kHz. See the following sections for further details.
GAIN AND PHASE GAIN AND PHASE
vs vs
FREQUENCY FREQUENCY
Figure 23. TPS54283 at 200-mAp-p Ripple Current Figure 24. TPS54283 at 400-mAp-p Ripple Current
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Product Folder Link(s): TPS54283 TPS54286