Datasheet

Feedback loop calculation guidelines AN4260
18/29 DocID024275 Rev 2
Equation 5
Equation 6
Equation 7
In the above formulas, C
OUT
and ESR are the capacitance and the equivalent series
resistance of the output capacitor respectively, Vy is the forward drop of the free-wheeling
diode, R
OUT
= V
OUT
/I
OUT
is the output load, Ipk is the drain peak current at full load and ∂ =
Ton*fsw is the duty cycle.
If just an RC series between COMP and GND is chosen as a compensation network, as
shown in Figure 2 (in fact Cc and CFB are not mounted), the mathematical expression of
the compensator C(f) is:
Equation 8
where:
Equation 9
and:
Equation 10
they are chosen in order to ensure the stability of the overall system.
The values of H
COMP
= δV
COMP
/δI
COMP
and of Gm (error amplifier transconductance) are
specified in the VIPER06 datasheet.
α
V
IN
Vγ+
V
OUT
Vγ+()
-----------------------------
Ipk
2
--------⋅=
β
V
IN
Vγ+
V
OUT
Vγ+()
2
-------------------------------
Ipk
2
-------- ∂⋅⋅=
G10
α R
OUT
⋅
1 β R
OUT
⋅+
-----------------------------
V
OUT
Vγ+()V
IN
Vγ+()
Ipk
2
-------- R
OUT
⋅⋅⋅
V
OUT
Vγ+()
2
V
IN
Vγ+()
Ipk
2
-------- ∂ R
OUT
⋅⋅⋅
-----------------------------------------------------------------------------------------------==
Gs()
C
0
H
COMP
---------------
1
jf⋅
fzc
--------+


j2π f⋅⋅⋅
-----------------------⋅=
C
0
Lfsw⋅
V
IN
V
OUT
–
-------------------------
Gm–
C7
--------------- -


R4
R4 R5+
----------------------⋅⋅=
fzc
1
2 π R3 C7⋅⋅ ⋅
------------------------------------=