L6714 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
L6714
STMicroelectronics
'L6714' PDF : 70 Pages View PDF
L6714
12.1
Voltage positioning
Droop function (Optional)
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 Figure 11, the ESR drop is present in any case, but using the droop function
the 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 beacomes a
requirement of the load.
Connecting DROOP pin and FB pin together, the device forces a current IDROOP,
proportional to the read current, into the feedback resistor RFB implementing the load
regulation dependence. Since IDROOP depends on the current information about the three
phases, the output characteristic vs. load current is then given by:
VOUT = VREF – RFB ⋅
IDROOP = VREF – RFB ⋅
-R----S---E----N----S---E--
Rg
⋅
IOUT = VREF – RDROOP ⋅
IOUT
Where RSENSE is the chosen sensing element resistance (Inductor DCR or LS RdsON) and
IOUT is the output current of the system.
The whole power supply can be then represented by a "real" voltage generator with an
equivalent output resistance RDROOP and a voltage value of VREF. RFB resistor can be also
designed according to the RDROOP specifications as follow:
RFB = RDROOP ⋅
-------R-----g---------
RSENSE
Droop function is optional, in case it is not desired, the DROOP pin can be disconnected
from the FB and an information about the total delivered current becomes available for
debugging, and/or current monitoring. When not used, the pin can be shorted to SGND.
Figure 11. Voltage positioning (left) and droop function (right)
VREF
DROOP
FB
COMP VSEN
RF
CF
RFB
64k
64k
FBR FBG
To Vcore
(Remote Sense)
ESR Drop
VMAX
VNOM
VMIN
RESPONSE WITHOUT DROOP
RESPONSE WITH DROOP
37/70
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