AN1330 Datasheet, PDF (15/31 Pages) STMicroelectronics – Designing with the L5970D 1A high efficiency DC-DC converter

AN1330
Closing the loop
This means that even if the input voltage changes, the error amplifier does not change its
value to keep the loop in regulation, thus ensuring a better line regulation and line transient
response.
To sum up the Open Loop Gain can be written as:
Equation 15
G(s)
=
G_PWM(s)
•
-------^R-----²--------
R₁ + R₂
•
A_O(s)
•
A_LC(s)
Example:
Considering R_C = 2.7 kΩ, C_C = 22 nF and C_P = 220 pF, the poles and zeroes of A₀ are:
F_P1 = 9 Hz
F_P2 = 256 kHz
F_Z1 = 2.68 kHz
If L = 22 µH, C_OUT = 100 µF and ESR = 80 mΩ, the poles and zeroes of A_LC become:
F_PLC = 3.39 kHz
F₀ = 19.89 kHz
Finally R₁ = 5.6 kΩ and R₂ = 3.3 kΩ.
The gain and phase bode diagrams are plotted respectively in Figure 11 and Figure 12.
Figure 11. Module plot
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