Datasheet

AN4164 Feedback loop calculation guidelines
Doc ID 023660 Rev 1 23/38
7 Feedback loop calculation guidelines
7.1 Transfer function
The set PWM modulator + power stage is indicated with G1(f), while C(f) is the “controller”,
i.e. the network which is in charge to ensure the stability of the system.
The mathematical expression of the power plant G1(f) is the following:
Equation 2
where V
OUT
is the output voltage, Ipkp is the primary peak current, fp is the frequency of the
pole due to the output load and fz the frequency of the zero due to the ESR of the output
capacitor:
Equation 3
Equation 4
Figure 38. Control loop block diagram
AM11582v1
)
fp
j
(1),(
)
fz
(1V
)
p
2j
(1),(
)
z
2
(1V
=
I
V
(f)G
OUTOUT
pk
OUT
1
f
VdcfswIpkp
fj
f
VdcfswIpkp
fj
⋅
+⋅
⋅
+⋅
=
⋅⋅⋅
+⋅
⋅⋅⋅
+⋅
Δ
Δ
=
π
π
2ESR)+·(RC
1
fp
OUTOUT
⋅
=
π
·ESRC2
1
fz
OUT
⋅⋅
=
π