1 of 8
110602
FEATURES
Five 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 100ns
Lithium energy source is electrically
disconnected to retain freshness until power is
applied for the first time
Optional industrial (IND) temperature range
of -40
C to +85C
PIN ASSIGNMENT
PIN DESCRIPTION
A0A20 -
Address
Inputs
DQ0DQ7
- Data In/Data Out
CE
- Chip Enable
WE
- Write Enable
OE
- Output Enable
V
CC
- Power (+3.3V)
GND -
Ground
NC
- No Connect
DESCRIPTION
The DS1270W 16Mb nonvolatile (NV) SRAMs are 16,777,216-bit, fully static, NV SRAMs organized as
2,097,152 words by 8 bits. Each NV SRAM has a self-contained lithium energy source and control
circuitry that 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 that can be executed, and no
additional support circuitry is required for microprocessor interfacing.
DS1270W
3.3V 16Mb Nonvolatile SRAM
www.maxim-ic.com
13
1
2
3
4
5
6
7
8
9
10
11
12
14
35
36-Pin Encapsulated Package
740mil Extended
A18
A14
A7
A6
A5
A4
A3
A2
A0
A1
V
CC
A19
NC
A15
A17
WE
A13
A8
A9
A11
OE
A10
DQ7
CE
36
34
33
32
31
30
29
28
27
26
25
23
24
A20
A16
A12
NC
DQ0
DQ1
15
16
22
21
DQ6
DQ5
17
18
GND
DQ2
DQ3
DQ4
19
20
DS1270W
2 of 8
READ MODE
The DS1270 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 21 address inputs
(A
0
A
20
) defines which of the 2,097,152 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
(Output Enable) 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 DS1270 devices execute a write cycle whenever
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 DS1270W provides full-functional capability for V
CC
greater than 3.0V and write protects by 2.8V.
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
protect themselves, all inputs become don't care, and all outputs become high-impedance. As V
CC
falls
below approximately 2.5V, a power-switching circuit connects the lithium energy source to RAM to
retain data. During power-up, when V
CC
rises above approximately 2.5V, the power-switching circuit
connects external V
CC
to RAM and disconnects the lithium energy source. Normal RAM operation can
resume after V
CC
exceeds 3.0V.
FRESHNESS SEAL
Each DS1270 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.
DS1270W
3 of 8
ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground
-0.3V to +4.6V
Operating Temperature Range
0C to 70C (-40C to +85C for IND parts)
Storage Temperature Range
-40C to +70C (-40C to +85C for IND parts)
Soldering Temperature
+260C 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
(
T
A
: See Note 10
)
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS NOTES
Power-Supply Voltage
V
CC
3.0
3.3
3.6
V
Logic 1 Input Voltage
V
IH
2.2
V
CC
V
Logic 0 Input Voltage
V
IL
0.0
+0.4
V
DC ELECTRICAL CHARACTERISTICS (T
A
: See Note 10; V
CC
= 3.3V
0.3V)
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS NOTES
Input Leakage Current
I
IL
-4.0
+4.0
mA
I/O Leakage Current
I
IO
-4.0
+4.0
mA
Output Current at 2.2V
I
OH
-1.0
mA
Output Current at 0.4V
I
OL
2.0
mA
Standby Current
CE
= 2.2V
I
CCS1
150
300
mA
Standby Current
CE
= V
CC
- 0.2V
I
CCS2
100
200
mA
Operating Current
I
CCO1
50
mA
Write Protection Voltage
V
TP
2.8
2.9
3.0
V
CAPACITANCE
(
T
A
= +25
C)
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS NOTES
Input Capacitance
C
IN
20
40
pF
Input/Output Capacitance
C
I/O
20
40
pF
PDF 
ZIP
