L6714 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
L6714
STMicroelectronics
'L6714' PDF : 70 Pages View PDF
L6714
10.1
Current reading and current sharing loop
Low side current reading
When reading current across LS, the current flowing trough each phase is read using the
voltage drop across the low side MOSFET RdsON or across a sense resistor in its series and
it is internally converted into a current. The trans-conductance ratio is issued by the external
resistor Rg placed outside the chip between CSx- and CSx+ pins toward the reading points.
The current sense circuit tracks the current information for a time TTRACK centered in the
middle of the LS conduction time and holds the tracked information during the rest of the
period.
L6714 sources a constant 25µA bias current from the CSx+ pin: the current reading circuitry
uses this pin as a reference and the reaction keeps the CSx- pin to this voltage during the
reading time (an internal clamp keeps CSx+ and CSx- at the same voltage sinking from the
CSx- pin the necessary current during the hold time; this is needed to avoid absolute
maximum rating overcome on CSx- pin). The current that flows from the CSx- pin is then
given by (See Figure 9):
ICSx-
=
25
µA
+
-R----d---s---O----N-
Rg
⋅
IPHASEx = 25µA + IINFOx
where RdsON is the ON resistance of the low side MOSFET and Rg is the trans-conductance
resistor used between CSx- and CSx+ pins toward the reading points; IPHASEx is the current
carried by the relative phase and IINFOx is the current information signal reproduced
internally.
25µA offset allows negative current reading, enabling the device to check for dangerous
returning current between the phases assuring the complete current equalization.
10.2
Inductor current reading
When reading current across the inductor DCR, the current flowing trough each phase is
read using the voltage drop across the output inductor or across a sense resistor in its
series and internally converted into a current. The trans-conductance ratio is issued by the
external resistor Rg placed outside the chip between CSx- pin toward the reading points.
The current sense circuit always tracks the current information, no bias current is sourced
from the CSx+ pin: this pin is used as a reference keeping the CSx- pin to this voltage. To
correctly reproduce the inductor current an R-C filtering network must be introduced in
parallel to the sensing element.
The current that flows from the CSx- pin is then given by the following equation (See
Figure 9):
ICSx-
=
-R----L--
Rg
⋅
-1----+-----s-----⋅-----L-----⁄------R-----L-
1+s⋅ R⋅ C
⋅
I
PHASEx
Where IPHASEx is the current carried by the relative phase.
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