L6713ATR datasheet(32/64 Pages) STMICROELECTRONICS

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Current reading and current sharing loop

L6713A

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Current reading and current sharing loop

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):

Where IPHASEx is the current carried by the relative phase.

Figure 8.

Current reading connections

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:

Where IINFOx is the current information reproduced internally.

CSx-

DCR

-------------

s L

DCR

()

⁄

⋅

1s R C

⋅⋅

------------------------------------------- I

⋅

PHASEx

⋅

CSx+

CSx-

PHASEx

DCRx

PHASEx

Inductor DCR Current Sense

ICSx-=IINFOx

NO Bias

DCR

-------------

CSx-

DCR

------------- I

PHASEx

⋅

⇒

⋅

INFOx

INFOX

DCR

------------- I

PHASEx

⋅

⇒

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