Datasheet

L6599 Application information
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After fixing CF in the hundred pF or in the nF (consistently with the maximum source
capability of the RF
min
pin and trading this off against the total consumption of the device),
the value of RF
min
and RF
max
will be selected so that the oscillator frequency is able to
cover the entire range needed for regulation, from the minimum value f
min
(at minimum input
voltage and maximum load) to the maximum value f
max
(at maximum input voltage and
minimum load):
A different selection criterion will be given for RF
max
in case burst-mode operation at no-load
will be used (see "Operation at no load or very light load" section).
Figure 23. Oscillator waveforms and their relationship with gate-driving signals
In Figure 23 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.
RF
min
1
3CFf
min
⋅⋅
------------------------------=
RF
max
RF
min
f
max
f
min
----------- 1–
-------------------- -=
CF
HVG
t
t
LVG
t
HB
t
T
D
T
D