Datasheet

REF LEVEL
0.000 dB
0.0 deg
100 1k
START 100.000 Hz
10k
STOP 100 000.000 Hz
/DIV
10.000 dB
45.000 deg
0
100k
GAIN
PHASE
REF LEVEL
0.000 dB
0.0 deg
100 1k
START 100.000 Hz
10k
STOP 100 000.000 Hz
/DIV
10.000 dB
45.000 deg
100k
GAIN
PHASE
0
LM25574, LM25574-Q1
www.ti.com SNVS483G –JANUARY 2007–REVISED APRIL 2013
Figure 17. Error Amplifier Gain and Phase
The overall loop can be predicted as the sum (in dB) of the modulator gain and the error amp gain.
Figure 18. Overall Loop Gain and Phase
If a network analyzer is available, the modulator gain can be measured and the error amplifier gain can be
configured for the desired loop transfer function. If a network analyzer is not available, the error amplifier
compensation components can be designed with the guidelines given. Step load transient tests can be
performed to verify acceptable performance. The step load goal is minimum overshoot with a damped response.
C6 can be added to the compensation network to decrease noise susceptibility of the error amplifier. The value
of C6 must be sufficiently small since the addition of this capacitor adds a pole in the error amplifier transfer
function. This pole must be well beyond the loop crossover frequency. A good approximation of the location of
the pole added by C6 is: f
p2
= fz x C5 / C6.
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