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FEATURES
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% VCC operating range (DS1249Y)
Optional ±=5% VCC operating range
(DS1249AB)
Optional industrial temperature range of
-40°C to +85°C, designated IND
JEDEC standard 32-pin DIP package
PIN ASSIGNMENT
PIN DESCRIPTION
A0 - A17 - Address Inputs
DQ0 - DQ7 - Data In/Data Out
CE - Chip Enable
WE - Write Enable
OE - Output Enable
VCC - Power (+5V)
GND - Ground
NC - 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 VCC 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.
DS1249Y/AB
2048k Nonvolatile SR AM
www.dalsemi.com
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31
32-Pin ENCAPSULATED PACKAGE
740-mil EXTENDED
A14
A7
A5
A4
A3
A2
A1
A0
DQ1
DQ0
V
CC
A
15
A
17
WE
A
13
A
8
A
9
A
11
OE
A
10
CE
DQ7
DQ5
DQ6
32
30
29
28
27
26
25
24
23
22
21
19
20
A16
A12
A6
NC
DQ2
GND 15
16
18
17 DQ4
DQ3
DS1249Y/AB
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READ MODE
The DS1249 devices ex ecute 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
(A0 - A17) defines which of the 262,144 bytes of data is accessed. Valid data will be available to the eight
data output drivers within tACC (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 f rom the later-occu rring signal (CE or OE ) and the limiting parameter is either tCO for
CE or tOE for OE rather than tACC.
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 ed ge 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 (tWR)
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 tODW from its falling edge.
DATA RETENTION MODE
The DS1249AB provides full functional capability for VCC greater than 4.75 volts and write protects by
4.5 volts. The DS1249Y provides full-functional capability for VCC greater than 4.5 volts and write
protects by 4.25 volts. Data is maintained in the absence of VCC without an y additional support circuitry.
The nonvolatile static RAMs constantly monitor VCC. 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 VCC falls below approximately 3.0 volts, a power switching circuit connects the lithium
energy source to RAM to retain data. During power-up, when VCC rises above approximately 3.0 volts,
the power switching circuit connects ex ternal VCC to the RAM and disconnects the lithium energ y source.
Normal RAM operation can resum e after VCC 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 VCC is first applied at a level greater than VTP, the lithium
energy source is enabled for battery backup operation.
DS1249Y/AB
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ABSOLUTE MAXIMUM RA TINGS*
Voltage on Any Pin Relative to Ground -0.3V to +7.0V
Operating Temperature 0°C to 70°C, -40°C to +85°C for IND parts
Storage Temperature -40°C to +70°C, -40°C to +85°C for IND parts
Soldering Temperature 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 (tA: See Note 10)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
DS1249AB Power Supply Voltage VCC 4.75 5.0 5.25 V
DS1249Y Power Supply Voltage VCC 4.5 5.0 5.5 V
Logic 1 VIH 2.2 VCC V
Logic 0 VIL 0.0 0.8 V
DC ELECTRICAL (VCC=5V ±=5% for DS1249AB)
CHARACTERISTICS (tA: See Note 10) (VCC=5V ±=10% for DS1249Y)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Input Leakage Current IIL -2.0 +2.0 µA
I/O Leakage Current CE ≥ VIH ≤ VCC IIO -2.0 +2.0 µA
Output Current @ 2.4V IOH -1.0 mA
Output Current @ 0.4V IOL 2.0 mA
Standby Current CE =2.2V ICCS1 1.0 1.5 mA
Standby Current CE =VCC-0.5V ICCS2 100 150 µA
Operating Current ICCO1 85 mA
Write Protection Voltage (DS1249AB) VTP 4.50 4.62 4.75 V
Write Protection Voltage (DS1249Y) VTP 4.25 4.37 4.5 V
CAPACITANCE (tA=25°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Input Capacitance CIN 10 20 pF
Input/Output Capacitance CI/O 10 20 pF
DS1249Y/AB
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AC ELECTRICAL (VCC=5V ±=5% for DS1249AB)
CHARACTERISTICS (tA: See Note 10) (VCC=5V ±=10% for DS1249Y)
DS1249AB-70
DS1249Y-70 DS1249AB-100
DS1249Y-100
PARAMETER SYMBOL MIN MAX MIN MAX UNITS NOTES
Read Cycle Time tRC 70 100 ns
Access Time tACC 70 100 ns
OE to Output Valid tOE 35 50 ns
CE to Output Valid tCO 70 100 ns
OE or CE to Output Active tCOE 5 5 ns 5
Output High Z from Deselection tOD 25 35 ns 5
Output Hold from Address Change tOH 55ns
Write Cycle Time tWC 70 100 ns
Write Pulse Width tWP 55 75 ns 3
Address Setup Time tAW 00ns
Write Recovery Time tWR1
tWR2
5
15 5
15 ns
ns 12
13
Output High Z from WE tODW 25 35 ns 5
Output Active from WE tOEW 5 5 ns 5
Data Setup Time tDS 30 40 ns 4
Data Hold Time tDH1
tDH2
0
10 0
10 ns
ns 12
13
DS1249Y/AB
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READ CYCLE
SEE NOTE 1
WRITE CYCLE 1
SEE NOTES 2, 3, 4, 6, 7, 8, and 12
DS1249Y/AB
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WRITE CYCLE 2
SEE NOTES 2, 3, 4, 6, 7, 8, and 13
POWER-DOWN/POWER-UP CONDITION
SEE NOTE 11
DS1249Y/AB
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POWER-DOWN/POWER-UP TIMING (tA: See Note 10)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
VCC Fail Detect to CE and WE Inactive tPD 1.5 µs11
VCC slew from VTP to 0V tF150 µs
VCC slew from 0V to VTP tR150 µs
VCC Valid to CE and WE Inactive tPU 2ms
VCC Valid to End of Write Protection tREC 125 ms
(tA=25°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Expected Data Retention Time tDR 10 years 9
WARNING:
Under no circumstance are negative undershoots, of any amplitude, allowed when device is in battery
backup mode.
NOTES:
1. WE is high for a Read Cycle.
2. OE = VIH or VIL. If OE = VIH during write cycle, the output buffers remain in a high impedance state.
3. tWP is specified as the logical AND of CE and WE . tWP is measured from the latter of CE or WE
going low to the earlier of CE or WE going high.
4. tDS is measured from the earlier of CE or WE going high.
5. These parameters are sampled with a 5 pF load and are not 100% tested.
6. If the CE low transition occurs simultaneously with or latter than the WE low transition in Write
Cycle 1, the output buffers remain in a high-impedance state during this period.
7. If the CE high transition occurs prior to or simultaneously with the WE high transition, the output
buffers remain in high-impedance state during this period.
8. If WE is low or the WE low transition occurs prior to or simultaneously with the CE low transition,
the output buffers remain in a high-impedance state during this period.
9. Each DS1249 has a built-in switch that disconnects the lithium source until VCC is first applied by the
user. The expected tDR is defined as accumulative time in the absence of VCC starting from the time
power is first applied by the user.
10. All AC and DC electrical characteristics are valid over the full operating temperature range. For
commercial products, this range is 0°C to 70°C. For industrial products (IND), this range is -40°C to
+85°C.
11. In a power-down condition the voltage on any pin may not exceed the voltage on VCC.
12. tWR1 and tDH1 are measured from WE going high.
13. tWR2 and tDH2 are measured from CE going high.
DS1249Y/AB
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DC TEST CONDITIONS AC TEST CONDITIONS
Outputs Open Output Load: 100 pF + 1TTL Gate
Cycle = 200 ns for operating current Input Pulse Levels: 0 - 3.0V
All voltages are referenced to ground Timing Measurement Reference Levels
Input: 1.5V
Output: 1.5V
Input pulse Rise and Fall Times: 5 ns
ORDERING INFORMATION
DS1249 TTP - SSS - III Operating Temperature Range
blank: 0° to 70°
IND: -40° to +85°C
Access Speed
70: 70 ns
100: 100 ns
Package Type
blank: 32-pin, 600-mil DIP
VCC Tolerance
Y: ±10%
AB: ±5%
DS1249Y/AB NONVOLATILE SRAM, 32-PIN, 740-MIL EXTENDED MODULE
PKG 32-PIN
DIM MIN MAX
A IN.
MM 2.080
52.83 2.100
53.34
B IN.
MM 0.715
18.16 0.740
18.80
C IN.
MM 0.395
10.03 0.405
10.29
D IN.
MM 0.280
7.11 0.310
7.49
E IN.
MM 0.015
0.38 0.030
0.76
F IN.
MM 0.120
3.05 0.160
4.06
G IN.
MM 0.090
2.29 0.110
2.79
H IN.
MM 0.590
14.99 0.630
16.00
J IN.
MM 0.008
0.20 0.012
0.30
K IN.
MM 0.015
0.43 0.025
0.58
