Datasheet

DocID14419 Rev 9 25/32
VIPER17 Operation descriptions
32
Fixed the V
INon
and the V
INoff
levels, with reference to Figure 31, the following relationships
can be established for the calculation of the resistors R
H
and R
L
:
Equation 9
Equation 10
For a proper operation of this function, V
IN on
must be less than the peak voltage at
minimum mains and V
IN off
less than the minimum voltage on the input bulk capacitor at
minimum mains and maximum load.
The BR pin is a high impedance input connected to high value resistors, thus it is prone to
pick up noise, which might alter the OFF threshold when the converter operates or gives
origin to undesired switch-off of the device during ESD tests.
It is possible to bypass the pin to ground with a small film capacitor (e.g. 1-10 nF) to prevent
any malfunctioning of this kind.
If the brown-out function is not used the BR pin has to be connected to GND, ensuring that
the voltage is lower than the minimum of V
DIS
threshold (50 mV, see Table 8). In order to
enable the brown-out function the BR pin voltage has to be higher than the maximum of
V
DIS
threshold (150 mV, see Table 8).
Figure 31. Brown-out protection: BR external setting and timing diagram
Rh
Rl
AC_OK Disable
-
+
BR
V
DIS
V
in_OK
Vcc
+
-
V
BRth
I
BRhyst
V
IN
V
IN
V
DRAIN
V
OUT
V
BR
V
BRth
V
in_OK
I
BR
t
t
t
t
t
t
t
V
INon
V
INoff
I
BRhyst
t
t
t
t
t
t
t
V
DD
V
DD
V
DDon
V
DDo
BRhyst
BRth
BRthINoff
BRhystINoffINon
BRhyst
BRhyst
L
I
V
VV
VVV
I
V
R ×
−
−−
+−=
BRhyst
BRhyst
L
L
BRhyst
BRhystINoffINon
H
I
V
R
R
I
VVV
R
+
×
−−
=