A6250X16W EMMICRO [EM Microelectronic - MARIN SA], A6250X16W Datasheet - Page 11

• Manufacturer Part Number: A6250X16W
• Description: High Efficiency Linear Power Supply with Accurate Power Surveillance and Software Monitoring
• Manufacturer: EMMICRO [EM Microelectronic - MARIN SA]

Typical Application
Timer Clearing and RES Action
The watch dog cir cuit mon i tors the ac tiv ity of the pro ces -
sor. If the user’s soft ware does not send a pulse to the TCL
in put within the pro grammed open win dow time out pe riod
a short watch dog RES pulse is gen er ated which is equal
to T
win dow con straint new se cu rity is added to con ven tional
watch dogs by mon i tor ing both soft ware cy cle time and
ex e cu tion. Should soft ware clear the watch dog too
quickly (in cor rect cy cle time) or too slowly (in cor rect ex e -
cu tion) it will cause the sys tem to be re set. If soft ware is
stuck in a loop which in cludes the rou tine to clear the
watch dog then a con ven tional watch dog would not make
a sys tem re set even though soft ware is mal func tion ing;
the A6250 would make a sys tem re set be cause the watch -
dog would be cleared too quickly. If no TCL sig nal is ap -
plied be fore the closed and open win dows ex pire, RES
will start to gen er ate square waves of pe riod (T
T
TCL fall ing edge ap pears dur ing an open win dow, or un til
a fresh power-up se quence. The sys tem en able out put,
EN, can be used to pre vent crit i cal con trol func tions be ing
ac ti vated in the event of the sys tem go ing into this fail ure
mode (see sec tion “En able - EN Out put"). The RES out put
must be pulled up to V
by the sys tem (see Fig. 8).
Com bined Voltage and Timer Action
The com bi na tion of volt age and timer ac tions is il lus trated
by the se quence of events shown in Fig. 6. On power-up,
when the volt age at V
POR, de lay is in i tial ized and holds RES ac tive for the time
WDR
WD
). The watch dog will re main in this state un til the next
/ 40 = 2.5 ms typ i cally (see Fig. 5). With the open
IN
OUTPUT
reaches V
even if the out put is not used
A6250
REF
, the power-on-reset,
CW
+ T
OW
+
of the POR de lay. A TCL pulse will have no ef fect un til this
power-on-reset de lay is com pleted. Af ter the POR de lay
has elapsed, RES goes in ac tive and the watch dog timer
starts act ing. If no TCL pulse oc curs, RES goes ac tive low
for a short time T
pe riod. A TCL pulse com ing dur ing the open win dow
clears the watch dog timer. When the TCL pulse oc curs
too early (dur ing the closed win dow), RES goes ac tive
and a new time out se quence starts. A volt age drop be low
the V
timer and im me di ately forces RES ac tive and EN in ac tive.
Any fur ther TCL pulse has no ef fect un til the next
power-up se quence has com pleted.
Enable - EN Output
The sys tem en able out put, EN, is in ac tive al ways when
RES is ac tive and re mains in ac tive af ter a RES pulse un til
the watch dog is ser viced cor rectly 3 con sec u tive times
(ie. the TCL pulse must come in the open win dow). Af ter
three con sec u tive ser vices of the watch dog with TCL dur -
ing the open win dow, the EN goes ac tive low. A mal func -
tion ing sys tem would be re peat edly re set by the
watch dog. In a con ven tional sys tem crit i cal mo tor con -
trols could be en er gized each time re set goes in ac tive
(time al lowed for the sys tem to re start) and in this way the
elec tri cal mo tors driven by the sys tem could func tion out
of con trol. The A6250 pre vents the above fail ure mode by
us ing the EN out put to dis able the mo tor con trols un til
soft ware has suc cess fully cleared the watch dog three
times (ie. the sys tem has cor rectly re started af ter a re set
con di tion).
REF
level for lon ger than typ i cally 5 µs over rides the
WDR
af ter each closed and open win dow
A6250
Fig. 18
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