System wake-up capability鈥?/div>
alarm interrupt output active in
battery-backup mode
廬
Less than 0.5碌A(chǔ) load under bat-
tery operation
廬
Selectable Intel or Motorola bus
timing
廬
24-pin plastic SOIC or SSOP
General Description
The CMOS bq3285EC/LC is a low-
power microprocessor peripheral pro-
viding a time-of-day clock and 100-
year calendar with alarm features
and battery operation. The architec-
ture is based on the bq3285/7 RTC
with added features: low-voltage op-
eration, 32.768kHz output, and an
extra 128 bytes of CMOS.
A 32.768kHz output is available for
sustaining power-management ac-
tivities. The bq3285EC 32kHz out-
put is always on whenever V
CC
is
valid. For the bq3285LC, the output
is on when the oscillator is turned
on. In V
C C
standby mode, the
32kHz is active, and the bq3285LC
typically draws 100碌A(chǔ) while the
bq3285EC typically draws 300碌A(chǔ).
Wake-up capability is provided by
an alarm interrupt, which is active
in battery-backup mode. In battery
backup mode, current drain is less
than 500nA.
The bq3285EC/LC 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 bq3285EC/LC is a fully com-
patible 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 bq3285EC is intended for use in
5V systems. The bq3285LC is in-
tended for use in 3V systems; the
bq3285LC, however, may also oper-
ate 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
鈥揂D
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鈥揦2
Data strobe input
V
CC
Read/write input
V
SS
Interrupt request output
Reset input
Ground
Power supply
Crystal inputs
3V backup cell input
RAM clear input
32K
32.768kHz output
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
EXTRAM Extended RAM enable
MOT
24-Pin SSOP
PN3285EC.eps
July 1996
1