bq3285EC/LC
(
)
Real-Time Clock RTC
in battery-backup mode. In battery
backup mode, current drain is less
than 500nA.
Features
General Description
➤ Direct clock/calendar replace-
ment for IBM® AT-compatible
computers and other applications
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.
The bq3285EC/LC write-protects the
clock, calendar, and storage registers
du r in g power fa ilu r e. A ba cku p
battery then maintains data and oper-
ates the clock and calendar.
➤ 2.7–5.5V operation (bq3285LC);
4.5–5.5V operation (bq3285EC)
➤ 242 bytes of general nonvolatile
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.
storage
➤ Dedicated 32.768kHz output pin
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 . I n VC C s t a n d by m od e, t h e
32kHz is active, and the bq3285LC
t ypica lly dr a ws 100µA wh ile t h e
bq3285EC typically draws 300µA.
Wake-up capability is provided by
an alarm interrupt, which is active
➤ System wake-up capability—
alarm interrupt output active in
battery-backup mode
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.
➤ Less than 0.5µA load under bat-
tery operation
➤ Selectable Intel or Motorola bus
timing
➤ 24-pin plastic SOIC or SSOP
Pin Connections
Pin Names
AD0–AD7 Multiplexed address/
data input/output
32K
32.768kHz output
EXTRAM Extended RAM enable
MOT
24
1
V
CC
MOT
CS
Bus type select input
Chip select input
Address strobe input
Data strobe input
Read/write input
Interrupt request output
Reset input
X1
X2
23
22
2
3
32k
EXTRAM
RCL
BC
RAM clear input
3V backup cell input
Crystal inputs
Power supply
Ground
4
RCL
BC
AD
AD
AD
AD
AD
AD
AD
21
20
19
18
17
16
15
14
13
0
1
2
3
4
5
6
5
AS
6
INT
RST
DS
V
SS
R/W
X1–X2
VCC
7
DS
8
9
R/W
INT
RST
10
11
12
VSS
AS
CS
AD
7
V
SS
24-Pin SSOP
PN3285EC.eps
July 1996
1