PC87307 datasheet(51/218 Pages) NSC

51 / 218 page

Real-Time Clock (RTC) and Advanced Power Control (APC) (Logical Device 2)

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Alarms

The timekeeping function may generate an alarm when the

current time reaches a stored alarm time. After each RTC

time update, the seconds, minutes, and hours storage loca-

tions are compared with the seconds, minutes and hours in

the alarm storage locations. If equal, the alarm flag is set in

Control Register C (CRC). If the Alarm Interrupt Enable

(AIE) bit is set in Control Register B (CRB), then setting the

Alarm Flag (AF) in CRC generates the IRQ internal interrupt

request (IRQ = 0).

Any alarm location, i.e., seconds, minutes or hours, may be

set to a “Don’t Care” state by setting bits 7,6 to 11. (This val-

ue is unused for either BCD or binary time codes.) This re-

sults in periodic alarm activation at an increased rate whose

period is that of the Don’t Care location, e.g., if the hours lo-

cation is set to 11, the alarm will be activated every hour.

The seconds, minutes and hours alarm registers are shared

with the wake-up function.

4.1.3

Power Supply

The host PC and part power is supplied by the system pow-

er supply voltage, VDD.

Figure 4-2 shows the power supplies of the part.

A stand-by voltage (VCCH) from the external AC power sup-

ply powers the RTC and APC under normal conditions. The

VDD voltage reaches the RTC/APC as a sense signal, to de-

termine the presence or absence of a valid VDD supply.

A battery backup voltage VBAT maintains RTC/APC time-

keeping and backup memory storage when the VCCH volt-

age is absent, due to power failure or disconnection of the

external AC input power supply.

The APC function produces the ONCTL signal, which con-

trols the VDD power supply voltage. (See Section 4.4.1 on

page 58.)

To ensure proper operation, a 500 mV differential is needed

between VCCH and VBAT.

Figure 4-3 represents a typical battery configuration. No ex-

ternal diode is required to meet the UL standard, due to the

internal serial resistor.

FIGURE 4-2. PC87307/PC97307 Power Supplies

FIGURE 4-3. Typical Battery Conﬁguration

Host PC

Power Supply Module

Backup

External AC Power

VDD

VCCH

VDD Power

VDD Sense

VCCH Power

VBAT Power

ONCTL

RTC

and

APC

Modules

PC87307/

Battery

PC97307

PC87307/

VBAT

0.1

VCCH

PC97307

PC87307 Datasheet(PDF) 51 Page - National Semiconductor (TI)

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