Features
a174 Direct clock/calendar replace-
ment for IBM
®
AT-compatible
computers and other applications
a174 2.7–5.5V operation (bq3285LC);
4.5–5.5V operation (bq3285EC)
a174 242 bytes of general nonvolatile
storage
a174 Dedicated 32.768kHz output pin
a174 System wake-up capability—
alarm interrupt output active in
battery-backup mode
a174 Less than 0.5µA load under bat-
tery operation
a174 Selectable Intel or Motorola bus
timing
a174 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 VCC is
valid. For the bq3285LC, the output
is on when the oscillator is turned
on. In VCC standby mode, the
32kHz is active, and the bq3285LC
typically draws 100µA while the
bq3285EC typically draws 300µA.
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.
1
1
PN3285EC.eps
24-Pin SSOP
2
3
4
5
6
7
8
24
23
22
21
20
19
18
17
9
10
16
15
11
12
14
13
V
CC
32k
EXTRAM
BC
INT
RST
DS
V
SS
R/W
AS
CS
MOT
X1
X2
AD
0
AD
1
AD
2
AD
3
AD
4
AD
5
AD
6
AD
7
V
SS
RCL
bq3285EC/LC
Pin Connections Pin Names
July 1996
AD0–AD7 Multiplexed address/
data input/output
MOT Bus type select input
CS Chip select input
AS Address strobe input
DS Data strobe input
R/W Read/write input
INT Interrupt request output
RST Reset input
32K 32.768kHz output
EXTRAM Extended RAM enable
RCL RAM clear input
BC 3V backup cell input
X1–X2 Crystal inputs
VCC Power supply
VSS Ground
Real-Time Clock
(
RTC
)