BQ3285EC Datasheet, PDF (1/26 Pages) Texas Instruments – Real-Time Clock (RTC)

bq3285EC/LC
Real-Time Clock ^(RTC)
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 0.5µA 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 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.
Pin Connections
Pin Names
MOT 1
X1 2
X2 3
AD0 4
AD1 5
AD2 6
AD3 7
AD4 8
AD5 9
AD6 10
AD7 11
VSS 12
24 VCC
23 32k
22 EXTRAM
21 RCL
20 BC
19 INT
18 RST
17 DS
16 VSS
15 R/W
14 AS
13 CS
July 1996
24-Pin SSOP
PN3285EC.eps
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
1
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