Datasheet

K
PWM
v
g
v
o
v
c
+
-
d
X
LC
V
ref
K
FB
Tv(s)
K
EA
TPS40200-Q1
SLUS739E SEPTEMBER 2006REVISED JULY 2013
www.ti.com
Frequency Compensation
The four elements that determine the system overall response are discussed in this section. The gain of the error
amplifier (K
EA
) is the first of these elements. Its output develops a control voltage that is the input to the PWM.
The TPS40200 has a unique modulator that scales the peak-to-peak amplitude of the PWM ramp to be 0.1 times
the value of the input voltage. Because modulator gain is given by V
IN
divided by V
RAMP
, the modulator gain is 10
and is constant at 10 (20 dB) over the entire specified input-voltage range.
The last two elements that affect system gain are the transfer characteristic of the output LC filter and the
feedback network from the output to the input to the error amplifier.
These four elements may be expressed by the following equation that represents the system transfer function as
shown in Figure 40.
T
V(S)
= K
FB
× K
EA
(S) × K
PWM
× X
LC
(S)
Where:
K
FB
= output voltage setting divider
K
EA
= error amplifier feedback
K
PWM
= modulator gain
X
LC
= filter transfer function
Figure 40. Control Loop
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