inputs, A(14:0); and eight bidirectional data lines, DQ(7:0). E1
and E2 are device enable inputs that control device selection,
active, and standby modes. Asserting both E1 and E2 enables
the device, causes I
DD
to rise to its active value, and decodes the
15 address inputs to select one of 32,768 words in the memory.
W controls read and write operations. During a read cycle, G
must be asserted to enable the outputs.
Table 1. Device Operation Truth Table
G
W
X
X
0
1
1
E1
X
1
0
0
0
E2
3
0
X
1
1
1
I/O Mode
3-state
3-state
Data in
3-state
Data out
Mode
Standby
Standby
Write
Read
2
Read
Figure 2a. SRAM Pinout (36)
X
1
X
X
1
A14
A12
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
V
SS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
V
DD
W
A13
A8
A9
A11
G
A10
E1
DQ7
DQ6
DQ5
DQ4
DQ3
0
Notes:
1. “X” is defined as a “don’t care” condition.
2. Device active; outputs disabled.
3. Tied active (i.e., logic 1) in the 28-pin DIP package.
READ CYCLE
A combination of W greater than V
IH
(min), E1 less than V
IL
(max), and E2 greater than V
IH
(min) defines a read cycle. Read
access time is measured from the latter of device enable, output
enable, or valid address to valid data output.
Read Cycle 1, the Address Access read in figure 3a, is initiated
by a change in address inputs while the chip is enabled with G
asserted and W deasserted. Valid data appears on data outputs
DQ(7:0) after the specified t
AVQV
is satisfied. Outputs remain
active throughout the entire cycle. As long as device enable and
output enable are active, the address inputs may change at a rate
equal to the minimum read cycle time (t
AVAV
).
Read Cycle 2, the Chip Enable-controlled Access in figure 3b,
is initiated by the latter of E1 and E2 going active while G
remains asserted, W remains deasserted, and the addresses
remain stable for the entire cycle. After the specified t
ETQV
is
satisfied, the eight-bit word addressed by A(14:0) is accessed
and appears at the data outputs DQ(7:0).
Read Cycle 3, the Output Enable-controlled Access in figure 3c,
is initiated by G going active while E1 and E2 are asserted, W
is deasserted, and the addresses are stable. Read access time is
t
GLQV
unless t
AVQV
or t
ETQV
have not been satisfied.
Figure 2b. SRAM Pinout (28)
PIN NAMES
A(14:0)
DQ(7:0)
E1
E2
1
Address
Data Input/Output
Enable 1
Enable 2
W
G
Write
Output Enable
V
DD
Power
V
SS
Ground
1. 36-lead flatpack only.
2
WRITE CYCLE
A combination of W less than V
IL
(max), E1 less than V
IL
(max),
and E2 greater than V
IH
(min) defines a write cycle. The state of
G is a “don’t care” for a write cycle. The outputs are placed in
the high-impedance state when either G is greater than
V
IH
(min), or when W is less than V
IL
(max).
Write Cycle 1, the Write Enable-controlled Access shown in
figure 4a, is defined by a write terminated by W going high, with
E1 and E2 still active. The write pulse width is defined by t
WLWH
when the write is initiated by W, and by t
ETWH
when the write
is initiated by the latter of E1 or E2. Unless the outputs have
been previously placed in the high-impedance state by G, the
user must wait t
WLQZ
before applying data to the eight
bidirectional pins DQ(7:0) to avoid bus contention.
Write Cycle 2, the Chip Enable-controlled Access shown in
figure 4b, is defined by a write terminated by the latter of E1 or
E2 going inactive. The write pulse width is defined by t
WLEF
when the write is initiated by W, and by t
ETEF
when the write
is initiated by the latter of E1 or E2 going active. For the W
initiated write, unless the outputs have been previously placed
in the high-impedance state by G, the user must wait t
WLQZ
before applying data to the eight bidirectional pins DQ(7:0) to
avoid bus contention.
RADIATION HARDNESS
The UT7156 SRAM incorporates special design and layout
features which allow operation in high-level radiation
environments.
Table 2. Radiation Hardness
Design Specifications
1
Total Dose
Error Rate
2
1.0E6
1.0E-10
rads(Si)
Errors/Bit-Day
Notes:
1. The SRAM will not latchup during radiation exposure under recommended
operating conditions.
2. 10% worst case particle environment, Geosynchronous orbit, 0.025 mils of
Aluminum.
3
ABSOLUTE MAXIMUM RATINGS
1
(Referenced to V
SS
)
SYMBOL
V
DD
V
I/O
T
STG
P
D
T
J
Θ
JC
I
I
PARAMETER
DC supply voltage
Voltage on any pin
Storage temperature
Maximum power dissipation
Maximum junction temperature
2
Thermal resistance, junction-to-case
3
DC input current
LIMITS
-0.5 to 7.0V
-0.5 to (V
DD
+ 0.3)V
-65 to +150°C
2.0W
+150°C
10°C/W
±
10 mA
Notes:
1. Stresses outside the listed absolute maximum ratings may cause permanent damage to the device. This is a stress rating only, functional operation of the device
and
at these or any other conditions beyond limits indicated in the operational sections of this specification is not recommended. E
xposure to absolute maximum rating
conditions for extended periods may affect device reliability.
2. Maximum junction temperature may be increased to +175C during burn-in and steady-static life.
°
3. Test per MIL-STD-883, Method 1012.
RECOMMENDED OPERATING CONDITIONS
SYMBOL
V
DD
T
C
V
IN
PARAMETER
Positive supply voltage
Case temperature range
DC input voltage
LIMITS
4.5 to 5.5V
-55 to +125°C
0V to V
DD
4
DC ELECTRICAL CHARACTERISTICS (Pre/Post-Radiation)*
(V
DD
= 5.0V±10%) (-55°C to +125°C)
SYMBOL
V
IH
V
IL
V
OL
V
OH
V
OH
C
IN1
C
IO1
I
IN
I
OZ
PARAMETER
High-level input voltage
Low-level input voltage
Low-level output voltage
High-level output voltage
High-level output voltage
Input capacitance
Bidirectional I/O capacitance
Input leakage current
Three-state output leakage current
(CMOS)
(CMOS)
I
OL
= 200µA, V
DD
= 4.5V (CMOS)
I
OH
= -200µA, V
DD
= 4.5V (CMOS)
I
OH
= -4mA, V
DD
= 4.5V (CMOS)
ƒ
= 1MHz @ 0V
ƒ
= 1MHz @ 0V
V
IN
= V
DD
and V
SS
V
O
= V
DD
and V
SS
V
DD
= 5.5V
G = 5.5V
I
OS2, 3
Short-circuit output current
V
DD
= 5.5V, V
O
= V
DD
V
DD
= 5.5V, V
O
= 0V
I
DD
(OP)
Supply current operating @1MHz
CMOS inputs (I
OUT
= 0)
V
DD
= 5.5V
I
DD1
(OP)
I
DD3
(SB)
4
Supply current operating
@ 25MHz
Supply current standby
@ 0Hz
CMOS inputs (I
OUT
= 0)
V
DD
= 5.5V
CMOS inputs (I
OUT
= 0)
E1 = V
DD
- 0.5, V
DD
= 5.5V
1.2
mA
120
mA
50
-90
+90
mA
mA
mA
-5
-10
V
DD
-0.05
4.2
4
7
5
10
CONDITION
MIN
3.5
1.5
0.05
MAX
UNIT
V
V
V
V
V
pF
pF
µA
µA
Notes:
* Post-radiation performance guaranteed at 25C per MIL-STD-883 Method 1019 at 5.0E rads(Si).
°
5
1. Measured only for initial qualification and after process or design changes that could affect input/output capacitance.
2. Supplied as a design limit but not guaranteed or tested.
3. Not more than one output may be shorted at a time for maximum duration of one second.
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