Datasheet

Table Of Contents
VIPER37 Operation description
Doc ID 022218 Rev 1 23/35
Figure 27. Timing diagram: behavior after short-circuit
8.6 Oscillator
The switching frequency is internally fixed to 60 kHz or 115 kHz. In both cases the switching
frequency is modulated by approximately ±4 kHz (60 kHz version) or ±8 kHz
(115 kHz version) at a 250 Hz (typ.) rate, so that the resulting spread-spectrum action
distributes the energy of each harmonic of the switching frequency over a number of side-
band harmonics having the same energy on the whole but smaller amplitudes.
8.7 Current mode conversion with adjustable current limit set
point
This device is a current mode converter: the drain current is sensed and converted into
voltage that is applied to the non-inverting pin of the PWM comparator. This voltage is
compared with the one on the feedback pin through a voltage divider on a cycle-by-cycle
basis.
The device has a default current limit value, I
Dlim
, that the user can adjust according to the
electrical specifications, through the R
LIM
resistor connected to the CONT pin (see
Figure 16
).
The CONT pin has a minimum current sunk, needed to activate the I
Dlim
adjustment: without
R
LIM
or with high R
LIM
(i.e. 100 k), the current limit is fixed to the default value (see I
Dlim
,
Tabl e 8
).
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