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TI-BQ4015.pdf
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TI-BQ4015.pdf
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1
Features
➤
Data retention for at least 10
years without power
➤
Automatic write-protection during
power-up/power-down cycles
➤
Conventional SRAM operation,
including unlimited write cycles
➤
Internal isolation of battery be
-
fore power application
➤
Industry standard 32-pin DIP
pinout
➤
34-pin LIFETIME LITHIUM™
module
-
Module completely
surface-mounted
-
Snap-on power-source for
lithium battery backup
-
Replaceable power-source
(part number: bq40MS)
General Description
The CMOS bq4015/Y is a nonvola
-
tile 4,194,304-bit static RAM organ
-
ized as 524,288 words by 8 bits. The
integral control circuitry and lith
-
ium energy source provide reliable
nonvolatility coupled with the un
-
limited write cycles of standard
SRAM.
The control circuitry constantly
monitors the single 5V supply for an
out-of-tolerance condition. When
V
CC
falls out of tolerance, the SRAM
is unconditionally write-protected to
prevent an inadvertent write opera
-
tion.
At this time the integral energy
source is switched on to sustain the
memory until after V
CC
returns
valid.
The bq4015/Y uses extremely low
standby current CMOS SRAMs, cou
-
pled with small lithium coin cells to
provide nonvolatility without long
write-cycle times and the write-cycle
limitations associated with EE
-
PROM.
The bq4015/Y requires no external
circuitry and is compatible with the
industry-standard 4Mb SRAM pin
-
out.
1
PN401501.eps
32-Pin DIP Module
2
3
4
5
6
7
8
32
31
30
29
28
27
26
25
9
10
24
23
11
12
22
21
13
14
20
19
15
16
18
17
V
CC
A
15
A
17
WE
A
13
A
8
A
9
A
11
OE
A
10
CE
DQ
7
DQ
6
DQ
5
DQ
4
DQ
3
A
18
A
16
A
14
A
12
A
7
A
6
A
5
A
4
A
3
A
2
A
1
A
0
DQ
0
DQ
1
DQ
2
V
SS
Pin Names
A0–A18 Address inputs
DQ0–DQ7 Data input/output
CE
Chip enable input
OE
Output enable input
WE
Write enable input
NC No connect
V
CC
Supply voltage input
V
SS
Ground
bq4015/Y
5/99 E
Pin Connections
512Kx8 Nonvolatile SRAM
PN4015Yncm.eps
34-Pin LIFETIME LITHIUM Module
11
12
13
14
15
16
17
1
2
3
4
5
6
7
8
9
10
24
23
22
21
20
19
18
34
33
32
31
30
29
28
27
26
25
NC
A15
A16
NC
V
CC
WE
OE
CE
DQ
7
DQ
6
DQ
5
DQ
4
DQ
3
DQ
2
DQ
1
DQ
0
V
SS
A18
A17
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
Selection Guide
Part
Number
Maximum
Access
Time (ns)
Negative
Supply
Tolerance
Part
Number
Maximum
Access
Time (ns)
Negative
Supply
Tolerance
bq4015x -70 70 -5% bq4015Yx -70 70 -10%
bq4015x -85 85 -5% bq4015Yx -85 85 -10%
Note: x = MA for PDIP or MS for LIFETIME LITHIUM module.
Functional Description
When power is valid, the bq4015/Y operates as a stan
-
dard CMOS SRAM. During power-down and power-up
cycles, the bq4015/Y acts as a nonvolatile memory, auto
-
matically protecting and preserving the memory con
-
tents.
Power-down/power-up control circuitry constantly moni
-
tors the V
CC
supply for a power-fail-detect threshold
V
PFD
. The bq4015 monitors for V
PFD
= 4.62V typical for
use in systems with 5% supply tolerance. The bq4015Y
monitors for V
PFD
= 4.37V typical for use in systems
with 10% supply tolerance.
When V
CC
falls below the V
PFD
threshold, the SRAM
automatically write-protects the data. All outputs be
-
come high impedance, and all inputs are treated as
“don’t care.” If a valid access is in process at the time of
power-fail detection, the memory cycle continues to com
-
pletion. If the memory cycle fails to terminate within
time t
WPT
, write-protection takes place.
As V
CC
falls past V
PFD
and approaches 3V, the control
circuitry switches to the internal lithium backup supply,
which provides data retention until valid V
CC
is applied.
When V
CC
returns to a level above the internal backup
cell voltage, the supply is switched back to V
CC
. After
V
CC
ramps above the V
PFD
threshold, write-protection
continues for a time t
CER
(120ms maximum) to allow for
processor stabilization. Normal memory operation may
resume after this time.
The internal coin cells used by the bq4015/Y have an ex
-
tremely long shelf life and provide data retention for
more than 10 years in the absence of system power.
As shipped from Unitrode, the integral lithium cells of
the MT-type module are electrically isolated from the
memory. (Self-discharge in this condition is approxi
-
mately 0.5% per year.) Following the first application of
V
CC
, this isolation is broken, and the lithium backup
provides data retention on subsequent power-downs.
The LIFETIME LITHIUM package option is shipped as
two parts.
2
bq4015/Y
Block Diagram
OE
A
0
–A
18
DQ
0
–DQ
7
WE
CE
Lithium
Cell
CE
CON
V
CC
1024K x 8
SRAM
Block
Power-Fail
Control
Power
BD4015.eps
3
bq4015/Y
Truth Table
Mode CE WE OE I/O Operation Power
Not selected H X X High Z Standby
Output disable L H H High Z Active
Read L H L D
OUT
Active
Write L L X D
IN
Active
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
-40 to +85 °C Industrial “N”
T
STG
Storage temperature
-40 to +70 °C Commercial
-40 to +85 °C Industrial “N”
T
BIAS
Temperature under bias
-10 to +70 °C Commercial
-40 to +85 °C Industrial “N”
T
SOLDER
Soldering temperature +260 °C For 10 seconds
Note: Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Functional operation
should be limited to the Recommended DC Operating Conditions detailed in this data sheet. Exposure to con
-
ditions beyond the operational limits for extended periods of time may affect device reliability.
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