Datasheet

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OUT
R2
V 0.696 1
R1
L
C
OUT
R
LOAD
V
OUT
R2
R1
+
V
REF
K
PWM
V
g
V
C
d
UDG-10220
TPS40200
SLUS659F –FEBRUARY 2006–REVISED MARCH 2012 www.ti.com
Voltage Setting and Modulator Gain
Since the input current to the error amplifier is negligible, the feedback impedance can be selected over a wide
range. Knowing that the reference voltage is 696 mV, choose a convenient value for R1 and then calculate the
value of R2 from Equation 2.
(7)
Figure 30. System Gain Elements
The error amplifier has a DC open loop gain of at least 60 dB with a minimum of a 1.5-MHz gain bandwidth
product which gives the user flexibility with respect to the type of feedback compensation he uses for his
particular application. The gain selected by the user at the crossover frequency is set to provide an over all unity
gain for the system. The crossover frequency should be selected so that the error amplifier open-loop gain is
high with respect to the required closed-loop gain, ensuring that the amplifier response is determined by the
passive feedback elements.
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