bq3285LF
Y2K-Enhanced
Real-Time Clock (RTC)
Features
®
ACPI-compliant day-of-month
alarm
®
Y2K century bit
®
Direct clock/calendar replace-
ment for IBM
®
AT-compatible
computers and other applications
®
2 index shadow registers
®
2.7–5.5V operation
®
240 bytes of general nonvolatile
storage
®
Dedicated 32.768kHz output pin
®
System wake-up capability—
alarm interrupt output active in
battery-backup mode
®
Less than 0.55µA load under bat-
tery operation
®
Selectable Intel or Motorola bus
timing
®
24-pin plastic SSOP
General Description
The CMOS bq3285LF is a low-power
microprocessor peripheral providing
a time-of-day clock and 100-year cal-
endar with alarm features and bat-
tery operation. The architecture is
based on the bq3285 RTC with added
features: century bit, low-voltage op-
eration, 32.768kHz output, 126 addi-
tional bytes of CMOS, two shadow
registers of last address used, and a
day-of-month alarm to be compliant
with the ACPI RTC specification.
A 32.768kHz output is available for
sustaining power-management ac-
tivities. The bq3285LF 32kHz out-
put is always on whenever V
CC
is
valid. In V
CC
standby mode, the
32kHz is active, and the bq3285LF
typically draws 100µA. Wake-up ca-
pability is provided by an alarm in-
terrupt, which is active in battery-
backup mode. In battery-backup
mode, current drain is less than
550nA.
The bq3285LF write-protects the
clock, calendar, and storage registers
during power failure. A backup
battery then maintains data and oper-
ates the clock and calendar.
The bq3285LF is a fully compatible
real-time clock for IBM AT-
compatible computers and other ap-
plications. The only external compo-
nents are a 32.768kHz crystal and a
backup battery.
The bq3285LF is intended for use in
3V systems; however, it may also op-
erate at 5V and then go into a 3V
power-down state, write-protecting
as if in a 3V system.
Pin Connections
Pin Names
AD
0
–AD
7
Multiplexed address/
data input/output
Bus type select input
RCL
CS
AS
DS
R/W
INT
RST
Chip select input
BC
Address strobe input
X1–X2
Data strobe input
V
CC
Read/write input
V
SS
Interrupt request output
Reset input
Ground
Supply voltage input
Crystal inputs
3V backup cell input
RAM clear input
32K
32.768kHz output
EXTRAM Extended RAM enable
MOT
X1
X2
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
VSS
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
VCC
32k
EXTRAM
RCL
BC
INT
RST
DS
VSS
R/W
AS
CS
MOT
24-Pin SSOP
PN3285ED/LD.eps
6/99 B
1
TI [ TEXAS INSTRUMENTS ]
