L6713A datasheet(56/64 Pages) STMICROELECTRONICS

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Tolerance band (TOB) definition

L6713A

56/64

23.2

Ext. current sense circuit tolerance (TOBCurrSense)

It can be further sliced as follow:

●

Inductor DCR Tolerance (kDCR). Variations in the inductor DCR impacts on the output

voltage since the device reads a current that is different from the real current flowing

into the sense element. As a results, the controller will source a IDROOP current different

from the nominal. The results will be an AVP different from the nominal in the same

percentage as the DCR is different from the nominal. Since all the sense elements

results to be in parallel, the error related to the inductor DCR has to be divided by the

number of phases (N).

●

Trans-conductance resistors tolerance (kRg). Variations in the Rg resistors impacts in

the current reading circuit gain and so impacts on the output voltage. The results will be

an AVP different from the nominal in the same percentage as the Rg is different from

the nominal. Since all the sense elements results to be in parallel, and so the three

current reading circuits, the error related to the Rg resistors has to be divided by the

number of phases (N).

●

NTC initial accuracy (kNTC_0). Variations in the NTC nominal value at room temperature

used for the thermal compensation impacts on the AVP in the same percentage as

before. In addition, the benefit of the division by the number of phases N cannot be

applied in this case.

●

NTC temperature accuracy (kNTC). NTC variations from room to hot also impacts on

the output voltage positioning. The impact is bigger as big is the temperature variation

from room to hot (

ΔT).

All these parameters impacts the AVP, so they must be weighted on the maximum voltage

swing from zero load up to the maximum electrical current (VAVP). Total error from external

current sense circuit results:

23.3

Time constant matching error tolerance (TOBTCMatching)

●

Inductance and capacitance tolerance (kL, kC). Variations in the inductance value and

in the value of the capacitor used for the time constant matching causes over/under

shoots after a load transient appliance. This impacts the output voltage and then the

TOB. Since all the sense elements results to be in parallel, the error related to the time

constant mismatch has to be divided by the number of phases (N).

●

Capacitance temperature variations (kCt). The capacitor used for time constant

matching also vary with temperature (

ΔT

C) impacting on the output voltage transients

ad before. Since all the sense elements results to be in parallel, the error related to the

time constant mismatch has to be divided by the number of phases (N).

All these parameters impact the dynamic AVP, so they must be weighted on the maximum

dynamic voltage swing (Idyn). Total error due to time constant mismatch results:

TOB

CurrSense

AVP

DCR

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

---------

NTC0

αΔTk

NTC

⋅⋅

DCR

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

⎝⎠

⎛⎞

⋅

TOB

TCMatching

AVPDyn

ΔTC

⋅

()

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

⋅

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