l6706 STMicroelectronics, l6706 Datasheet - Page 40

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

System control loop compensation
18
40/47
R
PWM
System control loop compensation
The control loop is an average current mode control loop (see
is equal to the reference programmed by VID minus the droop function terms.
The system control loop is reported in
the FB pin flows into R
current.
Figure 23. Main control loop
The control loop gain results (obtained opening the loop after the COMP pin):
Where:
DCR is the Inductor parasitic resistance;
Z
applied load R
Z
Z
A (s) is the error amplifier gain;
and has a typical value of 1.5 V.
Removing the dependence from the error amplifier gain, so assuming this gain high enough,
and with further simplifications, the control loop gain results:
The system control loop gain (see
to minimize static error and to cross the 0dB axes with a constant -20 dB/dec slope with the
DROOP
P
F
L
(s) is the impedance resulting by the parallel of the output capacitor (and its ESR) and the
(s) is the inductor impedance;
(s) is the compensation network impedance;
=
3
-- -
5
=
G LOOP s ( )
⋅
DCR
------------ - R
------------------ -
ΔV
Rg
V
OSC
IN
O
⋅
;
is the PWM transfer function where ΔV
G
FB
=
LOOP
–
is the equivalent output resistance determined by the droop function;
3
--- -
5
PWM
FB
⋅
--------------------- -
ΔV
s ( )
V
implementing the dependence of the output voltage from the read
OSC
IN
ERROR AMPLIFIER
COMP
=
⋅
–
Z
---------------
Doc ID 15698 Rev 1
R
-------------------------------------------------------------------------------------------------------------------
[
F
FB
Z
s ( )
P
Figure
s ( )
⋅
PWM Z
R
------------------------------------------- -
O
Figure
+
Z
L
R
+
F
Z
(s)
O
R
L
DROOP
+
⋅
23) is designed in order to obtain a high DC gain
s ( )
R
L
F
]
FB
24. The current information I
s ( )
⋅
V
REF
Z
--------------
⋅
⋅
A s ( )
------------------------------------------------------------------------------------------------------------------------------- -
s
F
(
2
R
s ( )
⋅
DROOP
C O L
1
+
+
C
⋅
⎛
⎝
s C
OUT
OSC
1
I
⋅
DROOP
+
+
Z
s
+
FB
O
⋅
----------- -
A s ( )
is the oscillator ramp amplitude
(s)
Z
⋅
-------- -
R O
1
(
R
P
L
R
Figure
OUT
s ( )
DROOP
+
⎞ R
⎠
C O ESR
⋅
)
FB
⋅
5): the output voltage
//R
O
+
DROOP
+
C O R L
ESR
⋅
)
sourced by
+
1
L6706