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FEATURES
10 years minimum data retention in the
absence of external power
Data is automatically protected during power
loss
Directly replaces 8k x 8 volatile static RAM
or EEPROM
Unlimited write cycles
Low-power CMOS
JEDEC standard 28-pin DIP package
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 (DS1225AD)
Optional ±5% VCC operating range
(DS1225AB)
Optional industrial temperature range of
-40°C to +85°C, designated IND
PIN ASSIGNMENT
28-Pin ENCAPSULATED PACKAGE
720-mil EXTENDED
PIN DESCRIPTION
A0-A12 - Address Inputs
DQ0-DQ7 - Data In/Data Out
CE - Chip Enable
WE - Write Ena ble
OE - Output Enable
VCC - Power (+5V)
GND - Ground
NC - No Connect
DESCRIPTION
The DS1225AB and DS1225AD are 65,536-bit, full y static, nonvolatile SRAMs organized as 8192 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. The NV SRAMs can be used in place of ex isting 8k x 8 SRAMs directly conforming to
the popular bytewide 28-pin DIP standard. The devices also match the pinout of the 2764 EPROM and
the 2864 EEPROM, allowing direct substitution while enhancing performance. There is no limit on the
number of write cycles that can be executed and no additional support circuitry is required for
microprocessor interfacing.
DS1225AB/AD
64k Nonvolatile SRAM
www.dalsemi.com
15
13
27
A7
A5
A3
A2
A1
A0
DQ0
DQ1
GND
DQ2
VCC
WE
NC
A
8
A
9
A
11
OE
A
10
CE
DQ7
DQ6
DQ5
DQ3
DQ4
1
2
3
4
5
6
7
8
9
10
11
12
14
28
26
25
24
23
22
21
20
19
18
17
16
A12
A6
A4
NC
DS1225AB/AD
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READ MODE
The DS1225AB and DS1225AD 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 13
address inputs (A0 -A12) defines which of the 8192 bytes of data is to be 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 CE and OE access times are not
satisfied, then data access must be measured from the later-occurring signal and the limiting parameter is
either tCO for CE or tOE for OE rather than address access.
WRITE MODE
The DS1225AB and DS1225AD execute 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 wr ite 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
recover y 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 tODW from its falling edge.
DATA RETENTION MODE
The DS1225AB provides full functional capability for VCC greater than 4.75 volts and write protects by
4.5 volts. The DS1225AD 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 any additional support circuitry.
The nonvolatile static RAMs constantly monitor VCC. 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 VCC falls below approximately 3.0 volts, the 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 external VCC to RAM and disconnects the lithium energy source.
Normal RAM operation can resum e after VCC exceeds 4.75 volts for the DS1225AB and 4.5 volts for the
DS1225AD.
FRESHNESS SEAL
Each DS1225 is shipped from Dallas Semiconductor with the lithium energy source disconnected,
guaranteeing full energy capacity. When VCC is first applied at a level of greater than VTP , the lithium
energy source is enabled for battery backup operation.
DS1225AB/AD
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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 e xtended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS (TA: See Note 10)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
DS1225AB Power Supply Voltage VCC 4.75 5.0 5.25 V
DS1225AD Power Supply Voltage VCC 4.50 5.0 5.5 V
Logic 1 VIH 2.2 VCC V
Logic 0 VIL 0.0 +0.8 V
(VCC =5V ± 5% for DS1225AB)
(TA: See Note 10)
DC ELECTRICAL CHARACTERISTICS (VCC =5V ± 10% for DS1225AD)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Input Leakage Current IIL -1.0 +1.0 µA
I/O Leakage Curr ent
CE> VIH< VCC IIO -1.0 +1.0 µA
Output Current @ 2.4V IOH -1.0 mA
Output Current @ 0.4V IOL 2.0 mA
Standby Current CE =2.2V ICCS1 5.0 10.0 mA
Standby Current CE =VCC -0.5V ICCS2 3.0 5.0 mA
Operating Current tCYC=200 ns
(Commercial) ICC01 75 mA
Operating Current tCYC=200 ns
(Industrial) ICC01 85 mA
Write Protection Voltage
(DS1225AB) VTP 4.50 4.62 4.75 V
Write Protection Voltage
(DS1225AD) VTP 4.25 4.37 4.5 V
CAPACITANCE (TA =25°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Input Capacitance CIN 510pF
Input/Output Capacitance CI/O 510pF
DS1225AB/AD
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(VCC =5V ± 5% for DS1225AB)
(TA: See Note 10)
AC ELECTRICAL CHARACTERISTICS (VCC =5V ± 10% for DS1225AD)
DS1225AB-70
DS1225AD-70 DS1220AB-85
DS1220AD-85
PARAMETER SYMBOL MIN MAX MIN MAX UNITS NOTES
Read Cycle Time tRC 70 85 ns
Access Time tACC 70 85 ns
OE to Output Valid tOE 35 45 ns
CE to Output Valid tCO 70 85 ns
OE or CE to Output Active tCOE 55ns5
Output High Z from Deselection tOD 25 30 ns 5
Output Hold from Address
Change tOH 55ns
Write Cycle Time tWC 70 85 ns
Write Pulse Width tWP 55 65 ns 3
Address Setup Time tAW 00 ns
Write Rec overy Time tWR1
tWR2
0
10 0
10 ns
ns 12
13
Output High Z from WE tODW 25 30 ns 5
Output Active from WE tOEW 55ns5
Data Setup Time tDS 30 35 ns 4
Data Hold Time tDH1
tDH2
0
10 0
10 ns
ns 12
13
DS1225AB/AD
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AC ELECTRICAL CHARACTERISTICS (cont’d)
DS1225AB- 150
DS1225AD- 150 DS1220AB-200
DS1220AD-200
PARAMETER SYMBOL MIN MAX MIN MAX UNITS NOTES
Read Cycle Time tRC 150 200 ns
Access Time tACC 150 200 ns
OE to Output Valid tOE 70 100 ns
CE to Output Valid tCO 150 200 ns
OE or CE to Output Active tCOE 55ns5
Output High Z from Deselection tOD 35 35 ns 5
Output Hold from Address
Change tOH 55ns
Write Cycle Time tWC 150 200 ns
Write Pulse Width tWP 100 100 ns 3
Address Setup Time tAW 00 ns
Write Rec overy Time tWR1
tWR2
0
10 0
10 ns
ns 12
13
Output High Z from WE tODW 35 35 ns 5
Output Active from WE tOEW 55ns5
Data Setup Time tDS 60 80 ns 4
Data Hold Time tDH1
tDH2
0
10 0
10 ns
ns 12
13
DS1225AB/AD
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READ CYCLE
SEE NOTE 1
WRITE CYCLE 1
SEE NOTES 2, 3, 4, 6, 7, 8 AND 12
WRITE CYCLE 2
SEE NOTES 2, 3, 4, 6, 7, 8 AND 13
DS1225AB/AD
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POWER-DOWN/POWER-UP CONDITION
SEE NOTE 11
POWER-DOWN/POWER-UP TIMING (TA : See Note 10)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
CE at VIH before Power-Down tPD 0µs11
VCC slew from VTP to 0VtF300 µs
VCC slew from 0V to VTP tR300 µs
CE at VIH after Power-Up tREC 2125 ms
(TA = 25°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Expected Data Retention Time tDR 10 years 9
WARNING:
Under no circumstance are neg ative undershoots, of any amplitude, allowed when device is in battery
backup mode.
DS1225AB/AD
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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 CEand WE . tWP is measured from the latter of CE or WE
going low to the earlier of CE or WE going high.
4. tDS are 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 later than the WE low transition, 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 a 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 DS1225AB and each DS1225AD 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 , tDH1 are measured from WE going high.
13. tWR2 , tDH2 are measured from CE going high.
14. DS1225AB and DS1225AD modules are recognized by Underwriters Laboratory (U.L.) under file
E99151.
DC TEST CONDITIONS
Outputs Open
All Voltages Are Referenced to Ground
AC TEST CONDITIONS
Output Load: 100 pF + 1TTL Gate
Input Pulse Levels: 0 - 3.0V
Timing Measurement Reference Levels
Input: 1.5V
Output: 1.5V
Input Pulse Rise and Fall Times: 5ns
DS1225AB/AD
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ORDERING INFORMATION
DS1225AB/AD
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DS1225AB/AD NONVOLATILE SRAM, 28-PIN, 720-MIL EXTENDED MODULE
PKG 28-PIN
DIM MIN MAX
A IN.
MM 1.520
38.61 1.540
39.12
B IN.
MM 0.695
17.65 0.720
18.29
C IN.
MM 0.395
10.03 0.415
10.54
D IN.
MM 0.100
2.54 0.130
3.30
E IN.
MM 0.017
0.43 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
0.38 0.021
0.53