Operation descriptions
VIPER27
7.9
About CONT pin
Referring to the
through the CONT pin, the below features can be implemented:
1.
2.
Current limit set point
Over voltage protection on the converter output voltage
The
referring to the
lists the external components needed to
activate one or plus of the CONT pin functions.
Figure 27. CONT pin configuration
Auxiliary
winding
R LIM
OVP
LOGIC
From RSENSE
OVP
Table 9.
CONT pin configurations
Function / component
I
Dlim
reduction
OVP
I
Dlim
reduction + OVP
R
LIM (1)
See
≥
80 k
Ω
See
R
OVP
No
See
Equation 4
See
Equation 4
D
AUX
No
Yes
Yes
1. R
LIM
has to be fixed before of R
OVP
7.10
Feed-back and overload protection (OLP)
The
VIPER27
is a current mode converter: the feedback pin controls the PWM operation,
controls the burst mode and actives the overload protection.
and
show the internal current mode structure.
With the feedback pin voltage between
V
FBbm
and
V
FBlin
, (see
the drain
current is sensed and converted in voltage that is applied to the non inverting pin of the
PWM comparator. See
This voltage is compared with the one on the feedback pin through a voltage divider on
cycle by cycle basis. When these two voltages are equal, the PWM logic orders the switch
off of the power MOSFET. The drain current is always limited to I
Dlim
value.
In case of overload the feedback pin increases in reaction to this event and when it goes
higher than
V
FBlin
, the PWM comparator is disabled and the drain current is limited to I
Dlim
by
the OCP comparator, seeFigure
20/31
Doc ID 15133 Rev 5
+
-
Daux
R OV P
CONT
SOFT
START
OCP
BLOCK
OCP
to GATE driver
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