L6567 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6567' PDF : 15 Pages View PDF
L6567
Other easy formulas fit rather well:
TDT ≅ 46.75 · 10^-12 · RREF
TPRE ≅ 224 · CP · RREF
As far as df/dt is concerned, there are no easy formulas that fit the relation between CF, RF, and CI. CI is charged
and discharged by three different currents that are derived from different mirroring ratios by the current flowing
on RREF. The voltage variations on CI are proportional to the current that charges CF, that is to say they are
proportional to df/dt.
The values obtained in the testing conditions (CI = 100nF) are:
during preheating and working conditions the typical frequency increase is ~ 20KHz/ms, the typical decrease is
~-10Khz/ms;
During ignition the frequency variation is ~ -200Hz/ms.
If slower variations are needed, CI has to be increased.
Due to these tight relationships, it is recommended to follow a precise procedure: first RHV has to be chosen
looking at startup current needs and dissipation problems. Then the feed forward frequency range has to be
determined, and so CF is set.
Given a certain CF, RREF is set in order to fix FMIN. Now CP can be chosed to set the desired TPRE and TIGN.
The other external parameters (RSHUNT and CI) can be chosen at the end because they are just related to a
single circuit parameters.
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