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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
TPS54383 , , TPS54386
SLUS774B – AUGUST 2007 – REVISED OCTOBER 2007
Figure 23. Small Signal Equivalent Block Diagram
The following figures plot the TPS5438x 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 20 kHz and 60 kHz. See the following sections for further details.
GAIN AND PHASE GAIN AND PHASE
vs vs
FREQUENCY FREQUENCY
Figure 24. TPS54383 at 200-mApp Ripple Current Figure 25. TPS54383 at 400-mApp Ripple Current
18 Submit Documentation Feedback Copyright © 2007, Texas Instruments Incorporated
Product Folder Link(s): TPS54383 TPS54386