MAXIM DS1225AB, DS1225AD User Manual
CE
WE
OE
DS1225AB/AD
64k Nonvolatile SRAM
www.maxim-ic.com
15
13
27
A7
A5
A3
A2
A1
A0
DQ0
DQ1
GND
DQ2
VCC
NC
A8
A9
A11
OE
A10
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
19-5625; Rev 11/10
FEATURES
10 years minimum data r etent ion in the
absence of external power
Data is automatically pro tected during power
loss
Directly replaces 8k x 8 volatile static RAM
or EE P R O M
Unlimited write c ycles
Low-power CMOS
JEDEC standard 28-pin DIP pack age
Read and write access times of 70 ns
Lithium energy sour ce is electrically
disconnected to retain freshness until power
is applied for the first time
Full ±10% VCC operating range (DS1225AD)
Optio na l ±5% V
(DS1225AB)
Optional industrial temperature range of
-40°C to +85°C, designated IND
operat ing range
CC
PIN ASSIGNMENT
28-Pin ENCAPSULATED PACKAGE
720-mil EXTENDED
PIN DESCRIPTION
A0-A12 - Address Inputs
DQ0-DQ7 - Data In/Data Out
- Chip Enable
- Write Enable
- Output Enable
V
- Power (+5V)
CC
GND - Ground
NC - No Co nne ct
DESCRIPTION
The DS1225AB and DS1225AD are 65,536-bit, fully 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 unconditio nally enabled to prevent
data corruption. The NV SRAMs can be used in place of existing 8k x 8 SRAMs directly conforming to
the popular bytewide 28-p in DIP standard. The devices also match the pinout of the 2764 EPROM and
the 2864 EEPROM, a llow ing dir ect s ubst itut ion wh ile en hanc ing pe rfor mance. Ther e is no lim it on t he
number of write cycles that can be executed and no additional support circuitry is required for
microprocesso r inter facing.
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READ MODE
WE
CE
OE
OE
WE
CE
WE
WE
WE
OE
WE
DS1225AB/AD
The DS1225AB and DS1225AD execute a read c ycle whenever
(Write Enable) is inactive (high) and
(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 t
stable, providing that CE and
access t imes a re als o sat isfied . If CE and
(Access T ime) after the last address input signal is
ACC
access t imes are not
satisfied, then data access must be measured fro m the later-oc cu rr ing s ig na l a nd t he li miting pa r a meter 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
(low) after addr ess inputs are st able. The later-occurring falling edge of CE or
start of the write cycle. The wr ite c ycle is ter minated by the ear lier r ising edge of CE or
inputs must be kept va lid t hroug hout the wr ite cy cle.
must ret urn to t he high s tat e for a min imu m
recovery t ime (tWR ) before ano ther c ycle can be initiated. The OE control signal should be kept inactive
(hig h) d ur ing wr ite cyc les t o avoid bus co ntent io n. Ho weve r, if t he ou tp ut d river s ar e e nable d (CE and
active) then
will disable the output s i n t
from its falling edge.
ODW
and
signals are active
w ill dete rmine t he
. All address
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-fu nctiona l capabilit y for VCC greater than 4.5 volts and write
protects by 4.25 volts. Data is maintained in the a bsence of VCC without any add itional support circuitry.
The nonvolatile stat ic RAMs constantly monitor VCC. Should the supply vo ltage decay, the NV SRAMs
automatically write protect themselves, all inputs become “don’t care,” and all outputs become highimpedance. As VCC falls below approximately 3.0 vo lts, the power switching circuit connect s the lithiu m
energy source to RAM to r etain data. During power-up , when VCC rises above approximately 3.0 volts,
the power sw itching c ircuit connect s external VCC to RAM and disconnects the lithium energy source.
Normal RAM operat ion can resu me after VCC exceeds 4.75 volts for the DS1225AB and 4.5 volts for the
DS1225AD.
FRESHNESS SEAL
Each DS1225 is shipped from Maxim with the lithium energy source disconnected, guaranteeing full
energy capacity. Whe n VCC is first applied at a level of great er than VTP , the lithium energ y source is
enabled for batt er y backup operation.
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DS1225AB/AD
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
Log ic 1
VIH
2.2 VCC V
Logic 0
VIL
0.0 +0.8 V
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
Input Leakage Current
A
I/O Leakage Current
CE
> VIH< VCC
Output Current @ 2.4V
IOH
-1.0
mA
Output Current @ 0.4V
IOL
2.0
mA
Standby Current CE =VCC -0.5V
Operating Current
(Commercial)
Operating Current
(Industrial)
Write Protection Voltage
(DS1225AB)
Write Protection Voltage
(DS1225AD)
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
Input Capacitance
CIN
5 10
pF
Input/Out put C apacitance
C
I/O
5 10
pF
ABSOLUTE MAXIMUM RATINGS
Voltage on Any Pin Relative to Ground -0.3V to +6.0V
Operating Temperat ur e
Commercial: 0°C to +70°C
Industrial: -40°C to +85°C
Storage Temperatu r e -40°C to +85°C
Lead Temperature (soldering, 10s) +260°C
Note: EDIP is wave or hand soldered only.
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)
(TA: See Note 10)
(V
=5V ± 5% for DS1225AB)
CC
DC ELECTRICAL CHARACTERISTICS (V
=5V ± 10% for DS1225AD)
CC
Standby Current CE =2.2V
IIL -1.0 +1.0
IIO -1.0 +1.0
I
5.0 10.0 mA
CCS1
I
3.0 5.0 mA
CCS2
I
75 mA
CC01
I
85 mA
CC01
µ
µA
VTP 4.50 4.62 4.75 V
VTP 4.25 4.37 4.5 V
CAPACITANCE (TA = +25°C)
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