L6599 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6599' PDF : 36 Pages View PDF
L6599
Application information
After fixing CF in the hundred pF or in the nF (consistently with the maximum source
capability of the RFmin pin and trading this off against the total consumption of the device),
the value of RFmin and RFmax will be selected so that the oscillator frequency is able to
cover the entire range needed for regulation, from the minimum value fmin (at minimum input
voltage and maximum load) to the maximum value fmax (at maximum input voltage and
minimum load):
RFmin=
-----------------1------------------
3 ⋅ CF ⋅ fmin
RFmax=
---R----F----m----i--n---
f--m-----a---x – 1
fmin
A different selection criterion will be given for RFmax in case burst-mode operation at no-load
will be used (see "Operation at no load or very light load" section).
Figure 22. Oscillator waveforms and their relationship with gate-driving signals
CF
HVG
TD
TD
t
LVG
t
HB
t
t
In Figure 22 the timing relationship between the oscillator waveform and the gate-drive
signals, as well as the swinging node of the half-bridge leg (HB) is shown. Note that the low-
side gate-drive is turned on while the oscillator's triangle is ramping up and the high-side
gate-drive is turned on while the triangle is ramping down. In this way, at start-up, or as the
IC resumes switching during burst-mode operation, the low-side MOSFET will be switched
on first to charge the bootstrap capacitor. As a result, the bootstrap capacitor will always be
charged and ready to supply the high-side floating driver.
17/36
Share Link: 
