Datasheet
Application information L6566B
38/51
Figure 25. Brownout protection: internal block diagram and timing diagram
The brownout comparator is provided with current hysteresis in addition to voltage
hysteresis: an internal 15 µA current sink is ON as long as the voltage applied on the
AC_OK pin is such that the AC_FAIL signal is high. This approach provides an additional
degree of freedom: it is possible to set the ON threshold and the OFF threshold separately
by properly choosing the resistors of the external divider (see below). With just voltage
hysteresis, instead, fixing one threshold automatically fixes the other one depending on the
built-in hysteresis of the comparator.
With reference to
Figure 25, the following relationships can be established for the ON
(Vsen
ON
) and OFF (Vsen
OFF
) thresholds of the sensed voltage:
Equation 16
which, solved for R
H
and R
L
, yield:
Equation 17
Sensed voltage
Vcc
(pin 5)
Vsen
ON
Vsen
OFF
GD
(pin 4)
Vout
VAC_OK
(pin 16)
I
HYS
15 µA
t
t
t
t
t
t
t
AC _ FAI L
0.45V
0.485V
-
+
L6566B
AC _ FAI L
AC_OK
Vcc
16
5
0.485V
0.45V
15 µA
R
H
RL
Sensed
voltage
LH
OFF
L
6
H
ON
R
45.0
R
45.0Vsen
R
485.0
1015
R
485.0Vsen
=
−
+⋅=
−
−
45.0Vsen
45.0
RR;
1015
Vsen078.1Vsen
R
OFF
HL
6
OFFON
H
−
=
⋅
⋅−
=
−