ADP315PC87570 National Semiconductor, ADP315PC87570 Datasheet - Page 67

• Manufacturer Part Number: ADP315PC87570
• Description: Keyboard and Power Management Controller
• Manufacturer: National Semiconductor

www.national.com
6.2.11 Alarms
The timekeeping function can be set to generate an alarm
when the current time reaches a stored alarm time. After
each RTC time update (every 1 second), the seconds, min-
utes, hours, day of the week, date of month, month and year
counters are compared with their corresponding registers in
the alarm settings. If equal, bit 5 (AF) of the CRC Register
is set. If the Alarm Interrupt Enable bit was previously set
(bit 5 of the CRB Register), IRQ8 interrupt request pin will
also go low (IRQ8 = 0). (Note: This pin is an open-drain out-
put and needs an external pull-up.)
Any alarm register may be set to “Don’t Care” by setting bits
7 and 6 to 11. This combination, not used by any BCD or bi-
nary time codes, results in a periodic alarm. The rate of this
periodic alarm is determined by the registers that were set
to “Don’t Care”.
For example, if only the seconds and minutes alarm regis-
ters are set to “Care”, an interrupt will be generated every
hour at the specified minute and second. If only the sec-
onds, minutes and hours alarm registers are set to “Care”,
an interrupt will be generated every day at the specified
hour, minute and second.
6.2.12 Power Supply
The PC87570 is supplied from two supply voltages, as
shown in Figure 6-4:
A standby (help) voltage (V
power supply powers the RTC and APC under normal con-
ditions.
Figure 6-5 represents a typical battery configuration. No ex-
ternal diode is required to meet the UL standard, due to the
internal switch and internal serial resistor R
System standby power supply voltage, V
Backup voltage, from low capacity Lithium battery.
PC87570
RTC
APC
and
Figure 6-4. Power Supply Connections
Host PC
V
PC0
V
BAT
CC
V
V
V
BAT
DD
SB
SB
Real-Time Clock (RTC) and Advanced Power Control (APC)
) from the external AC/DC
ONCTL
V
V
V
BAT
DD
SB
UL
AC Power
SB
ONCTL
V
.
External
V
Supply
Backup
Battery
Power
DD
SB
67
The RTC/APC module is supplied from one of two power
supplies, V
voltage comparator delivers the control signals to a pair of
switches. Battery backup voltage V
rect time and saves the CMOS memory when the V
age is absent, due to power failure or disconnection of the
external AC/DC input power supply or V
To assure that the module uses power from V
from V
minimum, as detailed in Table 19-8. "Voltage Thresholds"
on page 136.
The actual voltage point where the module switches from
V
voltage, but high enough to guarantee the correct function-
ality of the oscillator and the CMOS RAM.
Figure 6-6 shows typical battery current consumption dur-
ing battery-backed operation, and Figure 6-7 during normal
operation.
2. Place a 10-47 F capacitor on the common power
1. Place a 0.1 F capacitor on each V
BAT
Figure 6-6. Typical Battery Current During Battery
Figure 6-7. Typical Battery Current During Normal
RTC
APC
0.20
0.15
0.10
0.05
and
pin as close as possible to the pin, and also on V
supply net, as close as possible to the device.
I
Note: Battery voltage in this test is 3.0V.
BAT
to V
BAT
Figure 6-5. Typical Battery Configuration
V
( A)
PP
, the V
CC
CC
3.0 3.3 3.6
I
BAT
1.0
0.9
0.8
0.7
is lower than the minimum workable battery
or V
PC87570
CC
( A)
BAT
Backed Power Mode
voltage should be maintained above its
Operation Mode
, according to their levels. An internal
2.4 3.0 3.6
V
REF
R
4.5
UL
V
V
BAT
CC
BAT
V
BAT
CC
5.0
CC
maintains the cor-
0.1 F
0.1 F
power supply
(V)
main battery.
C
C
5.5
F
F
CC
and not
CC
V
(V)
BAT.
CC
BT
V
volt-
SB
1