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DS17285_1 Datasheet, PDF (23/31 Pages) Maxim Integrated Products – Real-Time Clocks
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Real-Time Clocks
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 VCC pin rises above the greater of
VBAT or VPF before the power-on timeout period (tPOTO)
expires, then PWR remains at the active-low level. If VCC
does not rise above the greater of VBAT or VPF 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
VBAT
VPF
*CONDITION
VPF < VBAT 0V
VPF
VBAT
*CONDITION
VBAT > VPF 0V
tPOTP
WF/KF
(INTERNAL)
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 VCC 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 VBAUX 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.
VIH
tKSPW
KS
VIL
VIH
PWR HIGH-IMPEDANCE
VIL
VIH
IRQ HIGH-IMPEDANCE
VIL
1
2
3
*THIS CONDITION CAN OCCUR WITH THE 3V DEVICE.
NOTE: THE TIME INTERVALS SHOWN ABOVE ARE REFERENCED IN THE WAKE-UP/KICKSTART SECTION.
4
5
Figure 6. Wake-Up/Kickstart Timing Diagram
Table 6. Wake-Up/Kickstart Timing
(TA =+25°C)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
Kickstart-Input Pulse Width
tKSPW
2
Wake-Up/Kickstart Power-On
Timeout
tPOTO
2
Note: Wake-up/kickstart timeout is generated only when the oscillator is enabled and the countdown chain is not reset.
UNITS
µs
s
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