L6713ATR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
L6713ATR
STMicroelectronics
'L6713ATR' PDF : 64 Pages View PDF
Current reading and current sharing loop
10 Current reading and current sharing loop
L6713A
L6713A embeds a flexible, fully-differential current sense circuitry that is able to read across
inductor parasitic resistance or across a sense resistor placed in series to the inductor
element. The fully-differential current reading rejects noise and allows placing sensing
element in different locations without affecting the measurement's accuracy.
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 8):
ICSx-
=
D-----C-----R---
Rg
⋅
1-----+-----s-----⋅---L-----⁄--(--D-----C-----R-----)
1+s⋅R⋅C
⋅
I
PHASE
x
Where IPHASEx is the current carried by the relative phase.
Figure 8. Current reading connections
PHASEx
IPHASEx
Lx DCRx
NO Bias
ICSx-=IINFOx
CSx+
CSx-
R
C
Rg
Inductor DCR Current Sense
Considering now to match the time constant between the inductor and the R-C filter applied
(Time constant mismatches cause the introduction of poles into the current reading network
causing instability. In addition, it is also important for the load transient response and to let
the system show resistive equivalent output impedance), it results:
------L------- = R ⋅ C
DCR
⇒
ICSx- =
D-----C-----R---
Rg
⋅
IPHASEx
=
IINFOx ⇒
IINFOX
=
D-----C-----R---
Rg
⋅
IPHASEx
Where IINFOx is the current information reproduced internally.
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