Datasheet

The timing associated with both the wake-up and kick-
starting sequences is illustrated in the Wake-
Up/Kickstart Timing Diagram (Figure 6). The timing
associated with these functions is divided into five inter-
vals, labeled 1 to 5 on the diagram.
The occurrence of either a kickstart or wake-up condition
causes the PWR pin to be driven low, as described
above. During interval 1, if the supply voltage on the
DS17x85/DS17x87 V
CC
pin rises above the greater of
V
BAT
or V
PF
before the power-on timeout period (t
POTO
)
expires, then PWR remains at the active-low level. If V
CC
does not rise above the greater of V
BAT
or V
PF
in this
time, then the PWR output pin is turned off and returns to
its high-impedance level. In this event, the IRQ pin also
remains tri-stated. The interrupt flag bit (either WF or KF)
associated with the attempted power-on sequence
remains set until cleared by software during a subse-
quent system power-on.
If V
CC
is applied within the timeout period, then the sys-
tem power-on sequence continue as shown in intervals
2 to 5 in the timing diagram. During interval 2, PWR
remains active and IRQ is driven to its active-low level,
indicating that either WF or KF was set in initiating the
power-on. In the diagram KS is assumed to be pulled
up to the V
BAUX
supply. Also at this time, the PAB bit is
automatically cleared to 0 in response to a successful
power-on. The PWR line remains active as long as the
PAB remains cleared to 0.
DS17285/DS17287/DS17485/DS17487/DS17885/DS17887
Real-Time Clocks
____________________________________________________________________ 23
Figure 6. Wake-Up/Kickstart Timing Diagram
Note: Wake-up/kickstart timeout is generated only when the oscillator is enabled and the countdown chain is not reset.
V
BAT
V
BAT
V
IH
t
KSPW
t
POTP
V
IH
V
IH
1
2
3
45
V
IL
V
IL
HIGH-IMPEDANCE
HIGH-IMPEDANCE
V
IL
V
PF
V
PF
0V
0V
*CONDITION
VPF
< VBAT
*THIS CONDITION CAN OCCUR WITH THE 3V DEVICE.
NOTE: THE TIME INTERVALS SHOWN ABOVE ARE REFERENCED IN THE WAKE-UP/KICKSTART SECTION.
*CONDITION
VBAT
> VPF
WF/KF
(INTERNAL)
KS
PWR
IRQ
Table 6. Wake-Up/Kickstart Timing
(T
A
=+25°C)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Kickstart-Input Pulse Width t
KSPW
2µs
Wake-Up/Kickstart Power-On
Timeout
t
POTO
2s