L6566B View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566B' PDF : 51 Pages View PDF
Application information
L6566B
Figure 25. Brownout protection: internal block diagram and timing diagram
Sensed
voltage
Vcc
L6566B
5
RH
AC_OK
-
16
0.485V +
15 µA 0.45V
RL
AC_FAIL
Sensed voltage
VsenON
VsenOFF
VAC_OK
(pin 16) 0.485V
AC_FAIL
IHYS
15 µA
Vcc
(pin 5)
GD
(pin 4)
Vout
t
0.45V
t
t
t
t
t
t
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
(VsenON) and OFF (VsenOFF) thresholds of the sensed voltage:
Equation 16
VsenON − 0.485 = 15 ⋅ 10 −6 + 0.485
RH
RL
VsenOFF − 0.45 = 0.45
RH
RL
which, solved for RH and RL, yield:
Equation 17
RH
=
Vsen ON
− 1.078 ⋅ VsenOFF
15 ⋅ 10 −6
;
RL
= RH
0.45
VsenOFF − 0.45
38/51
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