l6706 STMicroelectronics, l6706 Datasheet - Page 41

• Manufacturer Part Number: l6706
• Description: Vr11.1 Single Phase Controller With Integrated Driver
• Manufacturer: STMicroelectronics

L6706
desired crossover frequency ω
zero and two poles; both the poles are fixed once the output filter is designed (LC filter
resonance ω
Figure 24. Equivalent control loop block diagram (left) and bode diagram (right)
To obtain the desired shape an R
implementation. A zero at ω
integrator minimizes the static error while placing the zero ω
C resonance assures a simple -20 dB/dec shape of the gain.
In fact, considering the usual value for the output filter, the LC resonance results to be at
frequency lower than the above reported zero.
Compensation network can be simply designed placing ω
over frequency ω
1/10th of the switching frequency F
Moreover, it is suggested to filter the high frequency ripple on the COMP pin adding also a
capacitor between COMP pin and FB pin (it does not change the system bandwidth):
Z
F
(s)
FB
Z
FB
(s)
VREF
R
LC
F
C
P
) and the zero (ω
R
FB
T
COMP
C
as desired obtaining (always considering that ω
R
F
F
=
VSEN
R
--------------------------------- -
FB
PWM
F
⋅
V
= 1/R
ΔV
IN
Doc ID 15698 Rev 1
T
. Neglecting the effect of Z
FBG
d V
ESR
OSC
F
OUT
- C
F
SW
) is fixed by ESR and the droop resistance.
C
C
⋅
L
F
5
-- - ω
3
P
F
):
is then introduced together with an integrator. This
⋅
series network is considered for the Z
=
T
-------------------------------------- -
2 π R
C
ESR
O
⋅
⋅
---------------------------------------------- -
(
R
⋅
DROOP
V
OUT
1
F
⋅
F
L
R
SW
O
+
System control loop compensation
ESR
R
F
F
[dB]
F
K
(s), the transfer function has one
= ω
)
F
C
dB
in correspondence with the L-
F
LC
=
ω
and imposing the cross-
T
LC
------------------- -
might be not higher than
=
C
G
ω
R
LOOP
F
O
ω
F
ESR
⋅
(s)
L
F
(s)
Z
F
(s)
ω
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T
ω