bq3285ED/LD
(
)
Real-Time Clock RTC
Features
The bq3285ED/LD 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.
General Description
➤ ACPI-compliant
The CMOS bq3285ED/LD 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, 128 addi-
tional bytes of CMOS, and a day-of-
month alarm to be compliant with
the ACPI RTC specification.
day-of-month alarm
➤ Direct clock/calendar replace-
ment for IBM® AT-compatible
computers and other applications
The bq3285ED/LD 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.
➤ 2.7–5.5V operation (bq3285LD);
4.5–5.5V operation (bq3285ED)
➤ 242 bytes of general nonvolatile
storage
The bq3285ED is intended for use in
5V systems. The bq3285LD is in-
tended for use in 3V systems; the
bq3285LD, however, may also oper-
ate at 5V and then go into a 3V
power-down state, write-protecting
as if in a 3V system.
➤ Dedicated 32.768kHz output pin
A 32.768kHz output is available for
sustaining power-management ac-
tivities. The bq3285ED/LD 32kHz
output is always on whenever VCC is
valid. In VCC standby mode, the
32kHz is active, and the bq3285LD
t ypica lly dr a ws 100µA wh ile t h e
bq3285ED 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 550nA.
➤ System wake-up capability—
alarm interrupt output active in
battery-backup mode
➤ Less than 0.55µA load under bat-
tery operation
➤ Selectable Intel or Motorola bus
timing
➤ 24-pin plastic SSOP
Pin Connections
Pin Names
AD0–AD7 Multiplexed address/
data input/output
32K
32.768kHz output
EXTRAM Extended RAM enable
MOT
CS
Bus type select input
Chip select input
Address strobe input
Data strobe input
Read/write input
Interrupt request output
Reset input
MOT
24
1
V
CC
32k
EXTRAM
RCL
BC
RAM clear input
3V backup cell input
Crystal inputs
Power supply
Ground
X1
X2
23
22
2
3
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
AS
5
X1–X2
VCC
6
INT
RST
DS
V
SS
R/W
DS
7
8
9
R/W
INT
RST
VSS
10
11
12
AS
CS
AD
7
V
SS
24-Pin SSOP
PN3285ED/LD.eps
July 1997
1