Features
Direct clock/calendar replace-
ment for IBM
AT-compatible
computers and other applications
2.7–5.5V operation (bq3285LC);
4.5–5.5V operation (bq3285EC)
242 bytes of general nonvolatile
storage
Dedicated 32.768kHz output pin
System wake-up capability—
alarm interrupt output active in
battery-backup mode
Less than 0.5
μ
A load under bat-
tery operation
Selectable Intel or Motorola bus
timing
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
μ
A while the
bq3285E C typically draws 300
μ
A.
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.
battery then maintains data and oper-
ates theclock and calendar.
A backup
The bq3285E C/L C 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
2
3
4
5
6
7
8
9
10
11
12
PN3285EC.eps
24-Pin SSOP
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
X1
X2
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
VSS
bq3285EC/LC
Real-Time Clock (RTC)
Pin Connections
Pin Names
July 1996
AD
0
–AD
7
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
V
CC
Power supply
V
SS
Ground