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Электронный компонент: BQ4847YMT

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Features
Real-Time Clock counts seconds
through years in BCD format
Integrated battery and crystal
On-chip battery-backup switch-
over circuit with nonvolatile con-
trol for an external SRAM
130mAh battery capacity
1 minute per month clock accu-
racy
Less than 500nA of clock opera-
tion current in backup mode
Microprocessor reset valid to
V
CC
= V
SS
Independent watchdog timer
with a programmable time-out
period
Power-fail interrupt warning
Programmable clock alarm inter-
rupt active in battery-backup
mode
Programmable periodic interrupt
Battery-low warning
General Description
The bq4847 Real-Time Clock Mod-
ule is a low-power microprocessor
peripheral that integrates a time-
of-day clock, a 100-year calendar, a
CPU supervisor, a battery, and a crys-
tal in a 28-pin DIP module. The part
is ideal for fax machines, copiers, in-
dustrial control systems, point-of-sale
terminals, data loggers, and comput-
ers.
The bq4847 contains an internal
battery and crystal. Through the use
of the conditional chip enable output
(CE
OUT
) and battery voltage output
(V
OUT
) pins, the bq4847 can write-
protect and make nonvolatile an
external SRAM. The backup cell
powers the real-time clock and
maintains SRAM information in
the absence of system voltage.
T h e
b q 4 8 4 7
c o n t a i n s
a
temperature-compensated refer-
ence and comparator circuit that
monitors the status of its voltage
supply. When an out-of-tolerance
condition is detected, the bq4847
generates an interrupt warning
and subsequently a microproces-
sor reset. The reset stays active
for 200ms after V
CC
rises within
tolerance to allow for power supply
and processor stabilization.
The bq4847 also has a built-in
watchdog timer to monitor processor
operation. If the microprocessor does
not toggle the watchdog input (WDI)
within the programmed time-out,
the bq4847 asserts WDO and RST.
W D I u n c o n n e c t e d d i s a b l e s t h e
watchdog timer.
The bq4847 can generate other in-
terrupts based on a clock alarm con-
dition or a periodic setting.
The
alarm interrupt can be set to occur
from once per second to once per
month. The alarm can be made ac-
tive in the battery-backup mode to
serve as a system wake-up call. For
interrupts at a rate beyond once per
second, the periodic interrupt can be
programmed with periods of 30.5
s
to 500ms.
1
bq4847/bq4847Y
1
PN484701.eps
28-Pin DIP Module
2
3
4
5
6
7
8
28
27
26
25
24
23
22
21
9
10
20
19
11
12
18
17
13
14
16
15
VCC
WE
CEIN
CEOUT
NC
WDI
OE
CS
NC
DQ7
DQ6
DQ5
DQ4
DQ3
VOUT
NC
NC
WDO
INT
RST
A3
A2
A1
A0
DQ0
DQ1
DQ2
VSS
Pin Connections
A
0
A
3
Clock/Control address
inputs
DQ
0
DQ
7
Data inputs/outputs
WE
Write enable
OE
Output enable
CS
Chip select input
CE
IN
External RAM chip
enable
CE
OUT
Conditional RAM chip
enable
Pin Names
NC
No connect
V
OUT
Back-up battery output
INT
Interrupt output
RST
Microprocessor reset
WDI
Watchdog input
WDO
Watchdog output
V
CC
+5V supply
V
SS
Ground
RTC Module With CPU Supervisor
Caution:
Take care to avoid inadvertent dis-
charge through V
OUT
and
CE
OUT
after battery isolation has been
broken.
Sept. 1996
Functional Description
Figure 1 is a block diagram of the bq4847. The bq4847 is
functionally equivalent to the bq4845 except that the bat-
tery (20, 24) and crystal (2, 3) pins are not accessible. The
pins are connected internally to a coin cell and quartz
crystal. The coin cell provides 130mAh of capacity. It is in-
ternally isolated from V
OUT
and CE
OUT
until the initial
application of V
CC
. Once V
CC
rises above V
PFD
, this isola-
tion is broken, and the backup cell provides power to
V
OUT
and CE
OUT
for the external SRAM. The real-time
clock keeps time to within one minute per month at
room temperature. For a complete description of fea-
tures, operating conditions, electrical characteristics,
bus timing, and pin descriptions, see the bq4845 data
sheet. Valid part types for ordering are bq4847MT (5%)
and bq4847YMT (10%).
Figure 2 illustrates the address map for the bq4847. Ta-
ble 1 is a map of the bq4847 registers, and Table 2 de-
scribes the register bits.
2
Figure 1. Block Diagram
V
CC
CS
OE
WE
CE
OUT
V
OUT
Mode
DQ
Power
< V
CC
(max.)
V
IH
X
X
CE
IN
V
OUT1
Deselect
High Z
Standby
V
IL
X
V
IL
CE
IN
V
OUT1
Write
D
IN
Active
> V
CC
(min.)
V
IL
V
IL
V
IH
CE
IN
V
OUT1
Read
D
OUT
Active
V
IL
V
IH
V
IH
CE
IN
V
OUT1
Read
High Z
Active
< V
PFD
(min.) > V
SO
X
X
X
V
OH
V
OUT1
Deselect
High Z
CMOS standby
V
SO
X
X
X
V
OHB
V
OUT2
Deselect
High Z
Battery-backup mode
Truth Table
bq4847/bq4847Y
Sept. 1996
3
Ordering Information
Sept. 1996
MT: 28-Pin T-Type Module
28-Pin MT (T-Type Module)
Dimension
Inches
Millimeters
Min.
Max.
Min.
Max.
A
0.360
0.390
9.14
9.91
A1
0.015
-
0.38
-
B
0.015
0.022
0.38
0.56
C
0.008
0.013
0.20
0.33
D
1.520
1.535
38.61
38.99
E
0.710
0.740
18.03
18.80
e
0.590
0.620
14.99
15.75
G
0.090
0.110
2.29
2.79
L
0.110
0.130
2.79
3.30
S
0.100
0.120
2.54
3.05
bq4847
- MT
Package Option:
MT = 28-pin T-type Module
Voltage Tolerance:
Blank = 5%
Y = 10%
Device:
bq4847 Real-Time Clock Module With CPU Supervisor
bq4847/bq4847Y
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package
Type
Package
Drawing
Pins Package
Qty
Eco Plan
(2)
Lead/Ball Finish
MSL Peak Temp
(3)
BQ4847MT
ACTIVE
0
1
None
Call TI
Call TI
BQ4847YMT
ACTIVE
0
1
None
Call TI
Call TI
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in
a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - May not be currently available - please check
http://www.ti.com/productcontent
for the latest availability information and additional
product content details.
None: Not yet available Lead (Pb-Free).
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Green (RoHS & no Sb/Br): TI defines "Green" to mean "Pb-Free" and in addition, uses package materials that do not contain halogens,
including bromine (Br) or antimony (Sb) above 0.1% of total product weight.
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDECindustry standard classifications, and peak solder
temperature.
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PACKAGE OPTION ADDENDUM
www.ti.com
4-Mar-2005
Addendum-Page 1
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