L6714 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
L6714
STMicroelectronics
'L6714' PDF : 70 Pages View PDF
L6714
23
Tolerance band (TOB) definition
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:
TOBManuf = TOBC2 ontroller + TOBC2 urrSense + TOBT2 CMatching
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:
TOB = TOBManuf + VP + VTC
All the component spreads and variations are usually considered at 3σ. 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:
IDROOP
=
-R----S----E---N----S---E--
Rg
⋅
IOUT
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:
TOBController = [(VID – 19mV) ⋅ kVID]2 + (kIDROOP ⋅ RFB)2
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