Maximum duty cycle of PWM controller when synchronized?

[treez]

Hello,
The TLE8386 is a PWM controller than can be synchronized...on page 12 of the datasheet it says the sync signal can have a duty cycle anywhere between 20% and 80%. However, does that mean that the maximum duty cycle available is then limited to whatever duty cycle is used for the sync signal?

TLE8386 DATASHEET:
**broken link removed**

 

[FvM]

No, the datasheet says that the guaranteed maximum duty cycle is 90% in free running and 88% in sync mode in the specified +/- 20% pull range, independant of sync signal duty cycle.

 

[treez]

Right, I see what you mean, I missed that, as you say the sync'd duty cycle max is 88% so obviously the sync duty cycle can be anything from 20-80% as they only state 20-80%, and both of these are outside 88%.

They say that a frequency setting resistor must also be still used when sync'ing....they say that the frequency should be set to pretty much the same as what your sync frequency is......
This is presumably because of the slope compensation ramp(?), which presumably is set by the frequency resistor , and not the sync signal.

Given that this is because of the slope compensation, it seems obvious that if anything, the frequency setting resistor must set the frequency to slightly less than the sync signal......as such then the slope compensatory ramp will not transition too high during a period.
Would you say that this is the case? (that the frequency setting resistor should set the frequency to just less than the frequency sync'ing signal)?