Switching frequency of L4978 Buck?

[cupoftea]

Hi,
Do you know how to calc the switching frequency of an L4987 based Buck?

Pg 5 of datasheet gives the ramp peak....but there is no indication of what capacitor discharge current is then used to doscharge down to the trough. I took it that the ramp peak is a linear function and will find it by using "y=mx+c" and the two pais of values given.

L4978 datasheet

https://www.farnell.com/datasheets/1690386.pdf

 

[KlausST]

Figure 11

 

[cupoftea]

Thanks, yes i see Fig 11....the thing is, which Vin does that graph correspond to?.....page 5 tells that the oscillator upper threshold voltage varies widely with Vin...as such, the switching frequency will vary with the Vin.

 

[FvM]

the switching frequency will vary with the Vin.

It nearly doesn't. You want to read also Fig 12.