CY14B256L
256 Kbit (32K x 8) nvSRAM
Functional Description
■
25 ns, 35 ns, and 45 ns access times
■
Pin compatible with STK14D88
■
Hands off automatic STORE on power down with only a small
capacitor
■
STORE to QuantumTrap™ nonvolatile elements is initiated by
software, hardware, or AutoStore™ on power down
■
RECALL to SRAM initiated by software or power up
■
Unlimited READ, WRITE, and RECALL cycles
■
200,000 STORE cycles to QuantumTrap
The Cypress CY14B256L is a fast static RAM with a nonvolatile
element in each memory cell. The embedded nonvolatile
elements incorporate QuantumTrap technology producing the
world’s most reliable nonvolatile memory. The SRAM provides
unlimited read and write cycles, while independent, nonvolatile
data resides in the highly reliable QuantumTrap cell. Data
transfers from the SRAM to the nonvolatile elements (the
STORE operation) takes place automatically at power down. On
power up, data is restored to the SRAM (the RECALL operation)
from the nonvolatile memory. Both the STORE and RECALL
operations are also available under software control. A hardware
STORE is initiated with the HSB pin.
■
20 year data retention at 55°C
■
Single 3V +20%, –10% operation
■
Commercial and industrial temperature
■
32-pin (300 mil) SOIC and 48-pin (300 mil) SSOP packages
■
RoHS compliance
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Features
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Logic Block Diagram
VCC
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Quantum Trap
512 X 512
DQ 5
DQ 6
RECALL
STORE/
RECALL
CONTROL
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STATIC RAM
ARRAY
512 X 512
POWER
CONTROL
STORE
SOFTWARE
DETECT
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ROW DECODER
R
N
DQ 4
INPUT BUFFERS
DQ 2
DQ 3
ot
DQ 0
DQ 1
m
A5
A6
A7
A8
A9
A 11
A 12
A 13
A 14
VCAP
HSB
A13 - A 0
COLUMN I/O
COLUMN DEC
A 0 A 1 A 2 A 3 A 4 A 10
DQ 7
OE
CE
WE
Cypress Semiconductor Corporation
Document Number: 001-06422 Rev. *I
•
198 Champion Court
•
San Jose, CA 95134-1709
•
408-943-2600
Revised November 26, 2009
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CY14B256L
Contents
Features ...............................................................................1
Functional Description .......................................................1
Logic Block Diagram ..........................................................1
Contents ..............................................................................2
Pin Configurations .............................................................3
Pin Definitions ....................................................................3
Device Operation ................................................................4
SRAM Read .........................................................................4
SRAM Write .........................................................................4
AutoStore Operation ..........................................................4
Hardware STORE (HSB) Operation ...................................4
Hardware RECALL (Power Up) ..........................................5
Software STORE .................................................................5
Software RECALL ...............................................................5
Data Protection ...................................................................5
Noise Considerations .........................................................5
Low Average Active Power ................................................5
Preventing Store .................................................................6
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Best Practices ..................................................................... 6
Maximum Ratings ............................................................... 8
Operating Range ................................................................. 8
DC Electrical Characteristics ............................................ 8
Data Retention and Endurance ......................................... 8
Capacitance ........................................................................ 9
Thermal Resistance ............................................................ 9
AC Test Conditions ............................................................ 9
SRAM Read Cycle ......................................................10
SRAM Write Cycle .......................................................11
AutoStore or Power Up RECALL ....................................12
Software Controlled STORE/RECALL Cycle ..................13
Switching Waveforms ......................................................14
Part Numbering Nomenclature ........................................15
Ordering Information ........................................................15
Sales, Solutions, and Legal Information ........................19
Worldwide Sales and Design Support .........................19
Products ......................................................................19
Document Number: 001-06422 Rev. *I
Page 2 of 19
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CY14B256L
Pin Configurations
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Figure 1. Pin Diagram - 32-Pin SOIC and 48-Pin SSOP
Alt
IO Type
A0–A14
DQ0-DQ7
Input
CE
E
Input
G
Input
Ground
R
VSS
Write Enable Input, Active LOW. When the chip is enabled and WE is LOW, data on the IO
pins is written to the specific address location.
Chip Enable Input, Active LOW. When LOW, selects the chip. When HIGH, deselects the chip.
Output Enable, Active LOW. The active LOW OE input enables the data output buffers during
read cycles. Deasserting OE HIGH causes the IO pins to tri-state.
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W
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Input or Output Bidirectional Data IO Lines. Used as input or output lines depending on operation.
WE
OE
Address Inputs. Used to select one of the 32,768 bytes of the nvSRAM.
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Input
Description
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Pin Name
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Pin Definitions
Ground for the Device. The device is connected to ground of the system.
Power Supply Power Supply Inputs to the Device.
HSB
Input or Output Hardware Store Busy (HSB). When LOW, this output indicates a Hardware Store is in progress.
When pulled low external to the chip, it initiates a nonvolatile STORE operation. A weak internal
pull up resistor keeps this pin high if not connected (connection optional).
NC
N
VCAP
ot
VCC
Power Supply AutoStore Capacitor. Supplies power to nvSRAM during power loss to store data from SRAM
to nonvolatile elements.
No Connect
No Connect. This pin is not connected to the die.
Document Number: 001-06422 Rev. *I
Page 3 of 19
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CY14B256L
Device Operation
Figure 2 shows the proper connection of the storage capacitor
(VCAP) for automatic store operation. Refer to the DC Electrical
Characteristics on page 8 for the size of VCAP. The voltage on
the VCAP pin is driven to 5V by a charge pump internal to the chip.
A pull up is placed on WE to hold it inactive during power up.
The CY14B256L nvSRAM is made up of two functional components paired in the same physical cell. These are an SRAM
memory cell and a nonvolatile QuantumTrap cell. The SRAM
memory cell operates as a standard fast static RAM. Data in the
SRAM is transferred to the nonvolatile cell (the STORE
operation) or from the nonvolatile cell to SRAM (the RECALL
operation). This unique architecture enables the storage and
recall of all cells in parallel. During the STORE and RECALL
operations, SRAM READ and WRITE operations are inhibited.
The CY14B256L supports unlimited reads and writes similar to
a typical SRAM. In addition, it provides unlimited RECALL operations from the nonvolatile cells and up to 200K STORE operations.
Figure 2. AutoStore Mode
V CC
0.1UF
10k Ohm
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V CAP
WE
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SRAM Read
The CY14B256L performs a READ cycle whenever CE and OE
are LOW while WE and HSB are HIGH. The address specified
on pins A0–14 determines the 32,768 data bytes accessed. When
the READ is initiated by an address transition, the outputs are
valid after a delay of tAA (READ cycle 1). If the READ is initiated
by CE or OE, the outputs are valid at tACE or at tDOE, whichever
is later (READ cycle 2). The data outputs repeatedly respond to
address changes within the tAA access time without the need for
transitions on any control input pins, and remains valid until
another address change or until CE or OE is brought HIGH, or
WE or HSB is brought LOW.
V CC
V CAP
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SRAM Write
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A WRITE cycle is performed whenever CE and WE are LOW and
HSB is HIGH. The address inputs must be stable prior to entering
the WRITE cycle and must remain stable until either CE or WE
goes HIGH at the end of the cycle. The data on the common I/O
pins DQ0–7 are written into the memory if it has valid tSD, before
the end of a WE controlled WRITE or before the end of an CE
controlled WRITE. Keep OE HIGH during the entire WRITE cycle
to avoid data bus contention on common I/O lines. If OE is left
LOW, internal circuitry turns off the output buffers tHZWE after WE
goes LOW.
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AutoStore Operation
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The CY14B256L stores data to nvSRAM using one of three
storage operations:
1. Hardware store activated by HSB
2. Software store activated by an address sequence
3. AutoStore on device power down
AutoStore operation is a unique feature of QuantumTrap
technology and is enabled by default on the CY14B256L.
During normal operation, the device draws current from VCC to
charge a capacitor connected to the VCAP pin. This stored
charge is used by the chip to perform a single STORE operation.
If the voltage on the VCC pin drops below VSWITCH, the part
automatically disconnects the VCAP pin from VCC. A STORE
operation is initiated with power provided by the VCAP capacitor.
Document Number: 001-06422 Rev. *I
To reduce unnecessary nonvolatile stores, AutoStore and
Hardware Store operations are ignored, unless at least one
WRITE operation has taken place since the most recent STORE
or RECALL cycle. Software initiated STORE cycles are
performed regardless of whether a WRITE operation has taken
place. An optional pull-up resistor is shown connected to HSB.
The HSB signal is monitored by the system to detect if an
AutoStore cycle is in progress.
Hardware STORE (HSB) Operation
The CY14B256L provides the HSB pin for controlling and
acknowledging the STORE operations. The HSB pin is used to
request a hardware STORE cycle. When the HSB pin is driven
LOW, the CY14B256L conditionally initiates a STORE operation
after tDELAY. An actual STORE cycle only begins if a WRITE to
the SRAM takes place since the last STORE or RECALL cycle.
The HSB pin also acts as an open drain driver that is internally
driven LOW to indicate a busy condition, while the STORE
(initiated by any means) is in progress.
SRAM READ and WRITE operations, that are in progress when
HSB is driven LOW by any means, are given time to complete
before the STORE operation is initiated. After HSB goes LOW,
the CY14B256L continues SRAM operations for tDELAY. During
tDELAY, multiple SRAM READ operations take place. If a WRITE
is in progress when HSB is pulled LOW, it allows a time, tDELAY
to complete. However, any SRAM WRITE cycles requested after
HSB goes LOW are inhibited until HSB returns HIGH.
If HSB is not used, it is left unconnected.
Page 4 of 19
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CY14B256L
Hardware RECALL (Power Up)
Data Protection
During power up or after any low power condition (VCC <
VSWITCH), an internal RECALL request is latched. When VCC
once again exceeds the sense voltage of VSWITCH, a RECALL
cycle is automatically initiated and takes tHRECALL to complete.
The CY14B256L protects data from corruption during low
voltage conditions by inhibiting all externally initiated STORE
and WRITE operations. The low voltage condition is detected
when VCC is less than VSWITCH. If the CY14B256L is in a WRITE
mode (both CE and WE are low) at power up after a RECALL or
after a STORE, the WRITE is inhibited until a negative transition
on CE or WE is detected. This protects against inadvertent writes
during power up or brown out conditions.
Software STORE
Data is transferred from the SRAM to the nonvolatile memory by
a software address sequence. The CY14B256L software
STORE cycle is initiated by executing sequential CE controlled
READ cycles from six specific address locations in exact order.
During the STORE cycle, an erase of the previous nonvolatile
data is first performed followed by a program of the nonvolatile
elements. When a STORE cycle is initiated, input and output are
disabled until the cycle is completed.
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Noise Considerations
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The CY14B256L is a high speed memory. It must have a high
frequency bypass capacitor of approximately 0.1 µF connected
between VCC and VSS, using leads and traces that are as short
as possible. As with all high speed CMOS ICs, careful routing of
power, ground, and signals reduce circuit noise.
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Low Average Active Power
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CMOS technology provides the CY14B256L the benefit of
drawing significantly less current when it is cycled at times longer
than 50 ns. Figure 3 shows the relationship between ICC and
READ or WRITE cycle time. Worst case current consumption is
shown for both CMOS and TTL input levels (commercial temperature range, VCC = 3.6V, 100% duty cycle on chip enable). Only
standby current is drawn when the chip is disabled. The overall
average current drawn by the CY14B256L depends on the
following items:
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To initiate the software STORE cycle, the following READ
sequence is performed:
1. Read address 0x0E38, Valid READ
2. Read address 0x31C7, Valid READ
3. Read address 0x03E0, Valid READ
4. Read address 0x3C1F, Valid READ
5. Read address 0x303F, Valid READ
6. Read address 0x0FC0, Initiate STORE cycle
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Because a sequence of READs from specific addresses is used
for STORE initiation, it is important that no other READ or WRITE
accesses intervene in the sequence. If they intervene, the
sequence is aborted and no STORE or RECALL takes place.
The duty cycle of chip enable
■
The overall cycle rate for accesses
■
The ratio of READs to WRITEs
■
CMOS versus TTL input levels
■
The operating temperature
■
The VCC level
Software RECALL
■
I/O loading
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The software sequence is clocked with CE controlled READs or
OE controlled READs. When the sixth address in the sequence
is entered, the STORE cycle commences and the chip is
disabled. It is important that READ cycles and not WRITE cycles
are used in the sequence. It is not necessary that OE is LOW for
a valid sequence. After the tSTORE cycle time is fulfilled, the
SRAM is again activated for READ and WRITE operation.
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Data is transferred from the nonvolatile memory to the SRAM by
a software address sequence. A software RECALL cycle is
initiated with a sequence of READ operations in a manner similar
to the software STORE initiation. To initiate the RECALL cycle,
the following sequence of CE controlled READ operations is
performed:
1. Read address 0x0E38, Valid READ
2. Read address 0x31C7, Valid READ
3. Read address 0x03E0, Valid READ
4. Read address 0x3C1F, Valid READ
5. Read address 0x303F, Valid READ
6. Read address 0x0C63, Initiate RECALL cycle
Figure 3. Current vs. Cycle Time
Internally, RECALL is a two step procedure. First, the SRAM data
is cleared, and then the nonvolatile information is transferred into
the SRAM cells. After the tRECALL cycle time, the SRAM is once
again ready for READ and WRITE operations. The RECALL
operation does not alter the data in the nonvolatile elements. The
nonvolatile data can be recalled an unlimited number of times.
Document Number: 001-06422 Rev. *I
Page 5 of 19
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CY14B256L
Preventing Store
Best Practices
Disable the AutoStore function by initiating an AutoStore Disable
sequence. A sequence of READ operations is performed in a
manner similar to the software STORE initiation. To initiate the
AutoStore Disable sequence, perform the following sequence of
CE controlled or OE controlled READ operations:
1. Read Address 0x0E38 Valid READ
2. Read Address 0x31C7 Valid READ
3. Read Address 0x03E0 Valid READ
4. Read Address 0x3C1F Valid READ
5. Read Address 0x303F Valid READ
6. Read Address 0x03F8 AutoStore Disable
nvSRAM products have been used effectively for over 15 years.
While ease of use is one of the product’s main system values,
experience gained working with hundreds of applications has
resulted in the following suggestions as best practices:
■
Power up boot firmware routines should rewrite the nvSRAM
into the desired state. While the nvSRAM is shipped in a preset
state, the best practice is to again rewrite the nvSRAM into the
desired state as a safeguard against events that might flip the
bit inadvertently (program bugs, incoming inspection routines,
and so on).
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If the AutoStore function is disabled or re-enabled, a manual
STORE operation (Hardware or Software) is issued to save the
AutoStore state through subsequent power down cycles. The
part comes from the factory with AutoStore enabled.
■
If autostore is firmware disabled, it does not reset to “autostore
enabled” on every power down event captured by the nvSRAM.
The application firmware should re-enable or re-disable
autostore on each reset sequence based on the behavior
desired.
The VCAP value specified in this data sheet includes a minimum
and a maximum value size. Best practice is to meet this
requirement and not exceed the maximum VCAP value because
higher inrush currents may reduce the reliability of the internal
pass transistor. Customers that want to use a larger VCAP value
to make sure there is extra store charge should discuss their
VCAP size selection with Cypress to understand any impact on
the VCAP voltage level at the end of a tRECALL period.
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The nonvolatile cells in an nvSRAM are programmed on the
test floor during final test and quality assurance. Incoming
inspection routines at customer or contract manufacturer’s
sites sometimes reprogram these values. Final NV patterns are
typically repeating patterns of AA, 55, 00, FF, A5, or 5A. End
product’s firmware should not assume an NV array is in a set
programmed state. Routines that check memory content
values to determine first time system configuration, cold or
warm boot status, and so on should always program a unique
NV pattern (for example, complex 4-byte pattern of 46 E6 49
53 hex or more random bytes) as part of the final system
manufacturing test to ensure these system routines work
consistently.
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Re-enable the AutoStore by initiating an AutoStore Enable
sequence. A sequence of READ operations is performed in a
manner similar to the software RECALL initiation. To initiate the
AutoStore Enable sequence, perform the following sequence of
CE controlled or OE controlled READ operations:
1. Read Address 0x0E38 Valid READ
2. Read Address 0x31C7 Valid READ
3. Read Address 0x03E0 Valid READ
4. Read Address 0x3C1F Valid READ
5. Read Address 0x303F Valid READ
6. Read Address 0x07F0 AutoStore Enable
■
Document Number: 001-06422 Rev. *I
Page 6 of 19
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CY14B256L
Table 1. Hardware Mode Selection
H
L
L
H
L
Active[1, 2, 3]
Active ICC2[1, 2, 3]
Active[1, 2, 3]
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Active[1, 2, 3]
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Power
Standby
Active
Active
es
L
I/O
Output High Z
Output Data
Input Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output High Z
Output Data
Output Data
Output Data
Output Data
Output Data
Output High Z
D
H
Mode
Not Selected
Read SRAM
Write SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
AutoStore Disable
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
AutoStore Enable
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Nonvolatile Store
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Nonvolatile Recall
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A14 – A0
X
X
X
0x0E38
0x31C7
0x03E0
0x3C1F
0x303F
0x03F8
0x0E38
0x31C7
0x03E0
0x3C1F
0x303F
0x07F0
0x0E38
0x31C7
0x03E0
0x3C1F
0x303F
0x0FC0
0x0E38
0x31C7
0x03E0
0x3C1F
0x303F
0x0C63
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X
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WE
X
H
L
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CE
H
L
L
L
Notes
1. The six consecutive address locations are in the order listed. WE is HIGH during all six cycles to enable a nonvolatile cycle.
2. While there are 15 address lines on the CY14B256L, only the lower 14 lines are used to control software modes.
3. I/O state depends on the state of OE. The I/O table shown is based on OE Low.
Document Number: 001-06422 Rev. *I
Page 7 of 19
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CY14B256L
Package Power Dissipation
Capability (TA = 25°C) ................................................... 1.0W
Exceeding maximum ratings may shorten the useful life of the
device. These user guidelines are not tested.
Surface Mount Lead Soldering
Temperature (3 Seconds) .......................................... +260°C
Storage Temperature ................................. –65°C to +150°C
DC output Current (1 output at a time, 1s duration) .... 15 mA
Ambient Temperature with
Power Applied ............................................ –55°C to +125°C
Static Discharge Voltage.......................................... > 2001V
(MIL-STD-883, Method 3015)
Supply Voltage on VCC Relative to GND ..........–0.5V to 4.1V
Latch Up Current ................................................... > 200 mA
Voltage Applied to Outputs
in High Z State ....................................... –0.5V to VCC + 0.5V
Operating Range
Input Voltage...........................................–0.5V to Vcc + 0.5V
Range
Transient Voltage ( (VCC – 0.2V). All other inputs cycling.
tRC= 200 ns, 5V, 25°C Dependent on output loading and cycle rate. Values obtained
without output loads.
Typical
10
mA
ICC4
Average VCAP Current All Inputs Do Not Care, VCC = Max
during AutoStore Cycle Average current for duration tSTORE
3
mA
ISB
VCC Standby Current
3
mA
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ICC2
Input Leakage Current
VCC = Max, VSS < VIN < VCC
-1
+1
μA
Off State Output
Leakage Current
VCC = Max, VSS < VIN < VCC, CE or OE > VIH or WE < VIL
-1
+1
μA
VIH
Input HIGH Voltage
2.0
VCC +
0.5
V
VIL
VSS – 0.5
0.8
VOH
Output HIGH Voltage
IOUT = –2 mA
VOL
Output LOW Voltage
IOUT = 4 mA
VCAP
Storage Capacitor
Between VCAP pin and Vss, 6V rated.
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IOZ
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CE > (VCC – 0.2V). All others VIN < 0.2V or > (VCC – 0.2V).
Standby current level after nonvolatile cycle is complete.
Inputs are static. f = 0 MHz.
Input LOW Voltage
V
2.4
17
V
0.4
V
120
uF
Data Retention and Endurance
Min
Unit
DATAR
Parameter
Data Retention at 55°C
Description
20
Years
NVC
Nonvolatile STORE Operations
200
K
Note
4. The HSB pin has IOUT = –10 μA for VOH of 2.4 V. This parameter is characterized but not tested.
Document Number: 001-06422 Rev. *I
Page 8 of 19
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CY14B256L
Capacitance
In the following table, the capacitance parameters are listed.[5]
Parameter
Description
CIN
Input Capacitance
COUT
Output Capacitance
Test Conditions
TA = 25°C, f = 1 MHz,
VCC = 0 to 3.0V
Max
Unit
7
pF
7
pF
Thermal Resistance
In the following table, the thermal resistance parameters are listed.[5]
Description
Test Conditions
Thermal Resistance
(Junction to Ambient)
ΘJC
Test conditions follow standard test methods and
procedures for measuring thermal impedance, per
EIA / JESD51.
48-SSOP
Unit
42.36
44.26
°C/W
21.41
25.56
°C/W
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Thermal Resistance
(Junction to Case)
32-SOIC
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ΘJA
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Parameter
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Figure 4. AC Test Loads
R1 577Ω
3.0V
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3.0V
R1 577Ω For Tri-state Specs
Output
Output
5 pF
R2
789Ω
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R2
789Ω
30 pF
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AC Test Conditions
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Input Pulse Levels .................................................... 0V to 3V
Input Rise and Fall Times (10% - 90%)........................
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