DS1249Y/AB
2048k Nonvolatile SRAM
www.maxim-ic.com
FEATURES
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10 years minimum data retention in the
absence of external power
Data is automatically protected during power
loss
Unlimited write cycles
Low-power CMOS operation
Read and write access times as fast as 70 ns
Lithium energy source is electrically
disconnected to retain freshness until power is
applied for the first time
Full
±
10% V
CC
operating range (DS1249Y)
Optional
±
5% V
CC
operating range
(DS1249AB)
Optional industrial temperature range of
-40°C to +85°C, designated IND
JEDEC standard 32-pin DIP package
PIN ASSIGNMENT
NC
A16
A14
A12
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
V
CC
A15
A17
WE
A13
A8
A9
A11
OE
A10
CE
DQ7
DQ6
DQ5
DQ4
DQ3
32-Pin ENCAPSULATED PACKAGE
740-mil EXTENDED
PIN DESCRIPTION
A0 - A17
DQ0 - DQ7
CE
WE
OE
V
CC
GND
NC
- Address Inputs
- Data In/Data Out
- Chip Enable
- Write Enable
- Output Enable
- Power (+5V)
- Ground
- No Connect
DESCRIPTION
The DS1249 2048k Nonvolatile SRAMs are 2,097,152-bit, fully static, nonvolatile SRAMs organized as
262,144 words by 8 bits. Each NV SRAM has a self-contained lithium energy source and control circuitry
which constantly monitors V
CC
for an out-of-tolerance condition. When such a condition occurs, the
lithium energy source is automatically switched on and write protection is unconditionally enabled to
prevent data corruption. There is no limit on the number of write cycles which can be executed and no
additional support circuitry is required for microprocessor interfacing.
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DS1249Y/AB
READ MODE
The DS1249 devices execute a read cycle whenever
WE
(Write Enable) is inactive (high) and
CE
(Chip
Enable) and
OE
(Output Enable) are active (low). The unique address specified by the 18 address inputs
(A
0
- A
17
) defines which of the 262,144 bytes of data is accessed. Valid data will be available to the eight
data output drivers within t
ACC
(Access Time) after the last address input signal is stable, providing that
CE
and
OE
access times are also satisfied. If
OE
and
CE
access times are not satisfied, then data access
must be measured from the later-occurring signal (
CE
or
OE
) and the limiting parameter is either t
CO
for
CE
or t
OE
for
OE
rather than t
ACC
.
WRITE MODE
The DS1249 executes a write cycle whenever the
WE
and
CE
signals are active (low) after address
inputs are stable. The later-occurring falling edge of
CE
or WE will determine the start of the write cycle.
The write cycle is terminated by the earlier rising edge of
CE
or
WE
. All address inputs must be kept
valid throughout the write cycle.
WE
must return to the high state for a minimum recovery time (t
WR
)
before another cycle can be initiated. The
OE
control signal should be kept inactive (high) during write
cycles to avoid bus contention. However, if the output drivers are enabled (
CE
and
OE
active) then
WE
will disable the outputs in t
ODW
from its falling edge.
DATA RETENTION MODE
The DS1249AB provides full functional capability for V
CC
greater than 4.75 volts and write protects by
4.5 volts. The DS1249Y provides full-functional capability for V
CC
greater than 4.5 volts and write
protects by 4.25 volts. Data is maintained in the absence of V
CC
without any additional support circuitry.
The nonvolatile static RAMs constantly monitor V
CC
. Should the supply voltage decay, the NV SRAMs
automatically write protects themselves, all inputs become “don’t care,” and all outputs become high
impedance. As V
CC
falls below approximately 3.0 volts, a power switching circuit connects the lithium
energy source to RAM to retain data. During power-up, when V
CC
rises above approximately 3.0 volts,
the power switching circuit connects external V
CC
to the RAM and disconnects the lithium energy source.
Normal RAM operation can resume after V
CC
exceeds 4.75 volts for the DS1249AB and 4.5 volts for the
DS1249Y.
FRESHNESS SEAL
Each DS1249 device is shipped from Dallas Semiconductor with its lithium energy source disconnected,
guaranteeing full energy capacity. When V
CC
is first applied at a level greater than V
TP
, the lithium
energy source is enabled for battery backup operation.
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DS1249Y/AB
ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground
Operating Temperature
Storage Temperature
Soldering Temperature
*
-0.3V to +7.0V
0°C to 70°C, -40°C to +85°C for IND parts
-40°C to +70°C, -40°C to +85°C for IND parts
260°C for 10 seconds
This is a stress rating only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS
PARAMETER
DS1249AB Power Supply Voltage
DS1249Y Power Supply Voltage
Logic 1
Logic 0
SYMBOL
V
CC
V
CC
V
IH
V
IL
MIN
4.75
4.5
2.2
0.0
TYP
5.0
5.0
MAX
5.25
5.5
V
CC
0.8
(t
A
: See Note 10)
UNITS
V
V
V
V
NOTES
DC ELECTRICAL
CHARACTERISTICS
PARAMETER
Input Leakage Current
I/O Leakage Current
CE
³
V
IH
£
V
CC
Output Current @ 2.4V
Output Current @ 0.4V
Standby Current
CE
=2.2V
Standby Current
CE
=V
CC
-0.5V
Operating Current
Write Protection Voltage (DS1249AB)
Write Protection Voltage (DS1249Y)
(V
CC
=5V
±
5% for DS1249AB)
(t
A
: See Note 10) (V
CC
=5V
±
10% for DS1249Y)
SYMBOL
I
IL
I
IO
I
OH
I
OL
I
CCS1
I
CCS2
I
CCO1
V
TP
V
TP
4.50
4.25
4.62
4.37
MIN
-2.0
-2.0
-1.0
2.0
1.0
100
1.5
150
85
4.75
4.5
TYP
MAX
+2.0
+2.0
UNITS
mA
mA
mA
mA
mA
mA
mA
V
V
NOTES
CAPACITANCE
PARAMETER
Input Capacitance
Input/Output Capacitance
SYMBOL
C
IN
C
I/O
MIN
TYP
10
10
MAX
20
20
(t
A
=25°C)
UNITS
pF
pF
NOTES
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