l6706 STMicroelectronics, l6706 Datasheet - Page 21

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

L6706
8.2
where:
Offset resistor can be designed by considering the following relationship (RFB is fixed by the
Droop effect):
Offset automatically given by the DAC selection differs from the offset implemented through
the OFFSET pin: the built-in feature is trimmed in production and assures ±0.5% error over
load and line variations
Figure 7.
Droop function
This method “recovers” part of the drop due to the output capacitor ESR in the load
transient, introducing a dependence of the output voltage on the load current: a static error
proportional to the output current causes the output voltage to vary according to the sensed
current.
As shown in
total deviation of the output voltage is minimized. Moreover, more and more high-
performance CPUs require precise load-line regulation to perform in the proper way.
DROOP function is not then required only to optimize the output filter, but also becomes a
requirement of the load.
The device forces a current I
resistor implementing the load regulation dependence. Since I
current information, the output characteristic vs. load current is then given by (neglecting the
OFFSET voltage term):
Where DCR is the inductor parasitic resistance (or sense resistor when used) and I
the output current of the system. The whole power supply can be then represented by a
V
OUT
1.240V
=
Figure
Voltage positioning with positive offset
V
PROG
V
OFFSET
OUT
6, the ESR drop is present in any case, but using the droop function the
–
R
(
FB
I
OUT
R
⋅
OFFSET
I
DROOP
)
DROOP
=
To GND_core
Doc ID 15698 Rev 1
(Remote Sense)
V
V
PROG
PROG
R
, proportional to the read current, into the feedback R
=
FBG
FBG
OFFSET
V
V
OS
REF
–
GND DROP
RECOVERY
R
=
FB
To VCC_core
(Remote Sense)
–
R
=
R
FB
⋅
FB
R
I
⋅
DROOP
FB
------------------------
R
⋅
1.240V
DCR
------------ - I
OFFSET
⋅
Rg
1.240V
------------------ -
V
I
OFFSET
VSEN
(
OS
I
⋅
OUT
OUT
)
–
=
R
----------------------- -
R
FB
DROOP
1.240V
V
OFFSET
PROG
I
DROOP
FB
R
ERROR AMPLIFIER
V
F
depends on the
–
REF
Voltage positioning
R
DROOP
C
P
COMP
C
F
⋅
I
OUT
OUT
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is
FB