Features
Direct clock/calendar replace-
ment for IBM
AT-compatible
computers and other applications
Functionally compatible with the
DS1287/DS1287A and MC146818A
114 bytes of general nonvolatile
storage
Integral lithium cell and crystal
160 ns cycle time allows fast bus
operation
Selectable Intel or Motorola bus
timing
14 bytes for clock/calendar and
control
BCD or binary format for clock
and calendar data
Time of day in seconds, minutes,
and hours
-
12- or 24-hour format
-
Optional daylight saving
adjustment
Calendar in day of the week, day
of the month, months, and years
with automatic leap-year adjust-
ment
Programmable square wave out-
put
Three individually maskable in-
terrupt event flags:
-
Periodic rates from 122
s to
500 ms
-
Time-of-day alarm once per
second to once per day
-
End-of-clock update cycle
Better than one minute per
month clock accuracy
General Description
The CMOS bq3287/bq3287A is a
low-power microprocessor periph-
eral providing a time-of-day clock
and 100-year calendar with alarm
features and battery operation.
O t h e r f e a t u r e s i n cl u d e t h r e e
maskable interrupt sources, square-
wave output, and 114 bytes of gen-
e r a l n o n volatile storage. The
bq3287A version is identical to the
bq3287, with the addition of the RAM
clear input.
The bq3287 is a fully compatible
r e a l - t i m e c l o c k f o r I B M A T-
compatible computers and other ap-
p l i c a t i o n s. T h e b q 3 2 8 7 w r i t e -
protects the clock, calendar, and
storage registers during power fail-
ure. The integral backup energy
source then maintains data and op-
erates the clock and calendar.
As shipped from Benchmarq, the
real time clock is turned off to maxi-
mize battery capacity for in-system
operation.
The bq3287 is functionally equiva-
lent to the bq3285, except that the
battery (16, 20) and crystal (2, 3)
pins are not accessible. These pins
are connected internally to a coin
cell and quartz crystal. The coin cell
is sized to provide 10 years of data
retention and clock operation in the
absence of power. For a complete de-
scription of features, operating con-
ditions, electrical characteristics,
bus timing, and pin descriptions, see
the bq3285 data sheet.
1
Pin Names
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
1
PN328701.eps
24-Pin DIP Module
2
3
4
5
6
7
8
24
23
22
21
20
19
18
17
9
10
16
15
11
12
14
13
VCC
SQW
NC
NC
INT
RST
DS
NC
R/W
AS
CS
MOT
NC
NC
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
VSS
NC/RCL
Sept. 1996 D
RST
Reset input
SQW
Square wave output
NC
No connect
RCL
RAM clear input
(bq3287A only)
V
CC
+5V supply
V
SS
Ground
Pin Connections
bq3287/bq3287A
Real-Time Clock (RTC) Module
2
Sept. 1996 D
Recommended DC Operating Conditions
(TA = TOPR)
Symbol
Parameter
Minimum
Typical
Maximum
Unit
V
CC
Supply voltage
4.5
5.0
5.5
V
V
SS
Supply voltage
0
0
0
V
V
IL
Input low voltage
-0.3
-
0.8
V
V
IH
Input high voltage
2.2
-
V
CC
+ 0.3
V
Note:
Typical values indicate operation at T
A
= 25C.
Absolute Maximum Ratings
Symbol
Parameter
Value
Unit
Conditions
V
CC
DC voltage applied on V
CC
relative to V
SS
-0.3 to 7.0
V
V
T
DC voltage applied on any pin excluding V
CC
relative to V
SS
-0.3 to 7.0
V
V
T
V
CC
+ 0.3
T
OPR
Operating temperature
0 to +70
C
Commercial
-20 to +70
C
Extended "I"
T
STG
Storage temperature
-40 to +70
C
Commercial
-40 to +70
C
Extended "I"
T
BIAS
Temperature under bias
-10 to +70
C
Commercial
-20 to +70
C
Extended "I"
T
SOLDER
Soldering temperature
260
C
For 10 seconds
Note:
Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Functional opera-
tion should be limited to the Recommended DC Operating Conditions detailed in this data sheet. Expo-
sure to conditions beyond the operational limits for extended periods of time may affect device reliability.
DC Electrical Characteristics
(TA = TOPR, VCC = 5V
10%)
Symbol
Parameter
Minimum
Typical
Maximum
Unit
Conditions/Notes
I
LI
Input leakage current
-
-
1
A
V
IN
= V
SS
to V
CC
I
LO
Output leakage current
-
-
1
A
AD
0
AD
7
, INT and SQW
in high impedance
V
OH
Output high voltage
2.4
-
-
V
I
OH
= -1.0 mA
V
OL
Output low voltage
-
-
0.4
V
I
OL
= 4.0 mA
I
CC
Operating supply current
-
7
15
mA
Min. cycle, duty = 100%,
I
OH
= 0mA, I
OL
= 0mA
V
SO
Supply switch-over voltage
-
3.0
-
V
V
PFD
Power-fail-detect voltage
4.0
4.17
4.35
V
I
RCL
Input current when RCL = V
SS
-
-
185
A
Internal 30K pull-up
(bq3287A only)
I
MOTH
Input current when MOT =
V
CC
-
-
-185
A
Internal 30K pull-down
Note:
Typical values indicate operation at T
A
= 25C, V
CC
= 5V.
bq3287/bq3287A
3
Sept. 1996 D
Power-Down/Power-Up Timing
(TA = TOPR)
Symbol
Parameter
Minimum
Typical
Maximum
Unit
Conditions
t
F
V
CC
slew from 4.5V to 0V
300
-
-
s
t
R
V
CC
slew from 0V to 4.5V
100
-
-
s
t
CSR
CS at V
IH
after power-up
20
-
200
ms
Internal write-protection
period after V
CC
passes V
PFD
on power-up.
t
DR
Data-retention and time-
keeping time
10
-
-
years
T
A
= 25C.
Note:
Clock accuracy is better than
1 minute per month at 25C for the period of t
DR
.
Caution:
Negative undershoots below the absolute maximum rating of -0.3V in battery-backup mode
may affect data integrity.
Power-Down/Power-Up Timing
bq3287/bq3287A
5
Sept. 1996 D
bq3287/bq3287A
Ordering Information
Data Sheet Revision History
Change No.
Page No.
Description
Nature of Change
1
1
Address strobe input
Clarification
1
2
Power-fail detect voltage V
PFD
Was 4.1 min, 4.25 max;
is 4.0 min, 4.35 max
2
1
Was : "As shipped from Benchmarq, the backup cell
is electrically isolated from the memory. "
Is: "As shipped from Benchmarq, the backup cell is
electrically isolated from the active circuitry. "
Clarification
2
2, 4
Changed temperature from N (industrial, -40 to
+85C) to I (extended, -20 to +70C)
Specification change
3
2
I
RCL
max. was 275; is now 185. Pull-up = 30K
I
MOTH
max. was -275; is now -185. Pull-down = 30K Changed values
Notes:
Change 1 = Nov. 1992 B changes from June 1991 A.
Change 2 = Nov. 1995 C changes from Nov. 1992 B.
Change 3 = Sept. 1996 D changes from Nov. 1995 C.
*Contact factory for availability.
bq3287
MT -
Package Option:
MT = T-type module
Device:
bq3287 Real-Time Clock Module
RAM Clear Option:
A = RAM clear on pin 21
no mark = No connect on pin 21
Temperature:
blank = Commercial (0 to +70C)
I = Extended* (-20 to +70C)
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