DS17485S-5 查看數據表（PDF） - Maxim Integrated

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DS17485S-5

Real-Time Clocks

Maxim Integrated 

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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