L6714D datasheet(61/70 Pages) STMICROELECTRONICS

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L6714

Tolerance band (TOB) definition

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Tolerance band (TOB) definition

Output voltage load-line varies considering component process variation, system

temperature extremes, and age degradation limits. Moreover, individual tolerance of the

components also varies among designs: it is then possible to define a Manufacturing

Tolerance Band (TOBManuf) that defines the possible output voltage spread across the

nominal load line characteristic.

TOBManuf can be sliced into different three main categories: Controller Tolerance, External

Current Sense Circuit Tolerance and Time Constant Matching Error Tolerance. All these

parameters can be composed thanks to the RSS analysis so that the manufacturing

variation on TOB results to be:

Output voltage ripple (VP = VPP/2) and temperature measurement error (VTC) must be

added to the Manufacturing TOB in order to get the system Tolerance Band as follow:

All the component spreads and variations are usually considered at 3

σ. Here follows an

explanation on how to calculate these parameters for a reference L6714 application.

23.1

Controller tolerance (TOB controller)

It can be further sliced as follow:

●

Reference tolerance. L6714 is trimmed during the production stage to ensure the

output voltage to be within kVID = ±0.5% (±0.6% for AMD DAC) over temperature and

line variations. In addition, the device automatically adds a -19mV offset (Only for Intel

Mode) avoiding the use of any external component. This offset is already included

during the trimming process in order to avoid the use of any external circuit to generate

this offsets and, moreover, avoiding the introduction of any further error to be

considered in the TOB calculation.

●

Current Reading Circuit. The device reads the current flowing across the MOSFET

RdsON or the inductor DCR by using its dedicated differential inputs. The current

sourced by the VRD is then reproduced and sourced from the DROOP pin scaled down

by a proper designed gain as follow:

This current multiplied by the RFB resistor connected from FB pin vs. the load allows

programming the droop function according to the selected RL/Rg gain and RFB resistor.

Deviations in the current sourced due to errors in the current reading, impacts on the output

voltage depending on the size of RFB resistor. The device is trimmed during the production

stage in order to guarantee a maximum deviation of kIFB = ±1µA from the nominal value.

Controller tolerance results then to be:

TOB

Manuf

TOB

Controller

TOB

CurrSense

TOB

TCMatching

TOB

Manuf

DROOP

SENSE

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

OUT

⋅

TOB

Controller

VID

19mV

–

() k

VID

⋅

[]

IDROOP

⋅

()

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