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STK25C48
2K x 8 AutoStoreTM nvSRAM QuantumTrapTM CMOS Nonvolatile Static RAM
FEATURES
* Nonvolatile Storage without Battery Problems * Directly Replaces 2K x 8 Static RAM, BatteryBacked RAM or EEPROM * 20ns, 25ns, 35ns and 45ns Access Times * STORE to EEPROM Initiated by AutoStoreTM on Power Down * RECALL to SRAM Initiated by Software or Power Restore * 10mA Typical ICC at 200ns Cycle Time * Unlimited READ, WRITE and RECALL Cycles * 1,000,000 STORE Cycles to EEPROM * 100-Year Data Retention over Full Industrial Temperature Range * Commercial and Industrial Temperatures * 24-Pin 600 PDIP Package
DESCRIPTION
The STK25C48 is a fast SRAM with a nonvolatile EEPROM element incorporated in each static memory cell. The SRAM can be read and written an unlimited number of times, while independent nonvolatile data resides in the EEPROM. Data transfers from the SRAM to the EEPROM (the STORE operation) can take place automatically on power down using charge stored in system capacitance. Transfers from the EEPROM to the SRAM (the RECALL operation) take place automatically on restoration of power. The nvSRAM can be used in place of existing 2K x 8 SRAMs and also matches the pinout of 2K x 8 battery-backed SRAMs, EPROMs and EEPROMs, allowing direct substitution while enhancing performance. There is no limit on the number of read or write cycles that can be executed, and no support circuitry is required for microprocessor interfacing.
BLOCK DIAGRAM
EEPROM ARRAY 32 x 512 ROW DECODER VCC STORE/ RECALL CONTROL
PIN CONFIGURATIONS A
6
A5 A6 A7 A8 A9
STORE STATIC RAM ARRAY 32 x 512 RECALL
POWER CONTROL
A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 VSS
1 2 3 4 5 6 7 8 9 10 11 12
24 23 22 21 20 19 18 17 16 15 14 13
VCC A8 A9 W G A10 E DQ7 DQ6 DQ5 DQ4 DQ3 24 - 600 PDIP
DQ0 DQ1 DQ2 DQ3 DQ4 DQ5 DQ6 DQ7
INPUT BUFFERS
COLUMN I/O COLUMN DEC
PIN NAMES
A0 - A10 W Address Inputs Write Enable Data In/Out Chip Enable Output Enable Power (+ 5V) Ground
A0 A1 A2 A3 A4 A10
DQ0 - DQ7
G E W
E G VCC VSS
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STK25C48
ABSOLUTE MAXIMUM RATINGSa
Voltage on Input Relative to VSS . . . . . . . . . . -0.6V to (VCC + 0.5V) Voltage on DQ0-7 . . . . . . . . . . . . . . . . . . . . . . -0.5V to (VCC + 0.5V) Temperature under Bias . . . . . . . . . . . . . . . . . . . . . -55C to 125C Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . -65C to 150C Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1W DC Output Current (1 output at a time, 1s duration) . . . . . . . . 15mA
Note a: Stresses greater than those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only, and functional operation of the device at conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect reliability.
DC CHARACTERISTICS
COMMERCIAL SYMBOL ICC
c
(VCC = 5.0V 10%)b
INDUSTRIAL UNITS MIN MAX 95 85 75 65 3 10 2 30 25 21 18 1.5 1 5 2.2 VSS - .5 2.4 0.4 0 70 - 40 VCC + .5 0.8 2.2 VSS - .5 2.4 0.4 85 MIN MAX N/A 90 75 65 3 10 2 N/A 26 22 19 1.5 1 5 VCC + .5 0.8 mA mA mA mA mA mA mA mA mA mA mA mA A A V V V V C tAVAV = 20ns tAVAV = 25ns tAVAV = 35ns tAVAV = 45ns All Inputs Don't Care, VCC = max W (V CC - 0.2V) All Others Cycling, CMOS Levels All Inputs Don't Care tAVAV = 20ns, E V IH tAVAV = 25ns, E V IH tAVAV = 35ns, E VIH tAVAV = 45ns, E VIH E (V CC - 0.2V) All Others VIN 0.2V or (VCC - 0.2V) VCC = max VIN = VSS to VCC VCC = max VIN = VSS to VCC, E or G V IH All Inputs All Inputs IOUT = - 4mA IOUT = 8mA NOTES
PARAMETER Average VCC Current
1
ICC ICC ICC ISB
d
2
c
Average VCC Current during STORE Average VCC Current at tAVAV = 200ns 5V, 25C, Typical Average VCAP Current during AutoStoreTM Cycle Average VCC Current (Standby, Cycling TTL Input Levels)
3
d
4
e
1
ISB
e
2
VCC Standby Current (Standby, Stable CMOS Input Levels) Input Leakage Current Off-State Output Leakage Current Input Logic "1" Voltage Input Logic "0" Voltage Output Logic "1" Voltage Output Logic "0" Voltage Operating Temperature
IILK IOLK VIH VIL VOH VOL TA
Note b: Note c: Note d: Note e:
The STK25C48-20 requires VCC = 5.0V 5% supply to operate at specified speed. ICC and ICC are dependent on output loading and cycle rate. The specified values are obtained with outputs unloaded. 1 3 ICC and ICC are the average currents required for the duration of the respective STORE cycles (tSTORE ) . 2V will not produce standby current levels until any nonvolatile cycle in progress has timed out. 4 E IH 5.0V
AC TEST CONDITIONS
Input Pulse Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0V to 3V Input Rise and Fall Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5ns Input and Output Timing Reference Levels . . . . . . . . . . . . . . . 1.5V Output Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Figure 1
480 Ohms OUTPUT 255 Ohms
CAPACITANCEf
SYMBOL CIN COUT PARAMETER Input Capacitance Output Capacitance
(TA = 25C, f = 1.0MHz)
MAX 8 7 UNITS pF pF CONDITIONS
30 pF INCLUDING SCOPE AND FIXTURE
V = 0 to 3V V = 0 to 3V
Note f:
These parameters are guaranteed but not tested.
Figure 1: AC Output Loading
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STK25C48
SRAM READ CYCLES #1 & #2
SYMBOLS NO. 1 2 3 4 5 6 7 8 9 10 11 PARAMETER #1, #2 tELQV tAVAVg tAVQVh tGLQV tAXQXh tELQX tEHQZi tGLQX tGHQZi tELICCHf tEHICCL
e, f
(VCC = 5.0V 10%)b
STK25C48-20 STK25C48-25 MIN MAX 25 25 22 8 5 5 7 0 7 0 25 0 25 0 10 0 35 5 5 10 0 13 0 45 25 10 5 5 13 0 15 35 35 15 5 5 15 STK25C48-35 MIN MAX 35 45 45 20 STK25C48-45 UNITS MIN MAX 20 20 MIN MAX 45 ns ns ns ns ns ns ns ns ns ns ns
Alt. tACS tRC tAA tOE tOH tLZ tHZ tOLZ tOHZ tPA tPS Chip Enable Access Time Read Cycle Time Address Access Time Output Enable to Data Valid Output Hold after Address Change Chip Enable to Output Active Chip Disable to Output Inactive Output Enable to Output Active Output Disable to Output Inactive Chip Enable to Power Active Chip Disable to Power Standby
Note g: W must be high during SRAM READ cycles and low during SRAM WRITE cycles. Note h: I/O state assumes E, G < VIL and W > VIH; device is continuously selected. Note i: Measured + 200mV from steady state output voltage.
SRAM READ CYCLE #1: Address Controlledg, h
tAVAV ADDRESS
5 3 2
tAVQV DATA VALID
tAXQX DQ (DATA OUT)
SRAM READ CYCLE #2: E Controlledg
tAVAV ADDRESS tELQV E
6 tELQX 1 2
tEHICCL
7
1 1
tEHQZ
G tGLQV
4
tGHQZ
9
tGLQX DQ (DATA OUT)
10 tELICCH DATA VALID
8
ACTIVE
ICC
STANDBY
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STK25C48
SRAM WRITE CYCLES #1 & #2
SYMBOLS NO. #1 12 13 14 15 16 17 18 19 20 21 tAVAV tWLWH tELWH tDVWH tWHDX tAVWH tAVWL tWHAX tWLQZi, j tWHQX #2 tAVAV tWLEH tELEH tDVEH tEHDX tAVEH tAVEL tEHAX Alt. tWC tWP tCW tDW tDH tAW tAS tWR tWZ tOW Write Cycle Time Write Pulse Width Chip Enable to End of Write Data Set-up to End of Write Data Hold after End of Write Address Set-up to End of Write Address Set-up to Start of Write Address Hold after End of Write Write Enable to Output Disable Output Active after End of Write 5 PARAMETER MIN 20 15 15 8 0 15 0 0 7 5 MAX MIN 25 20 20 10 0 20 0 0 10 5 MAX MIN 35 25 25 12 0 25 0 0 13 5 MAX MIN 45 30 30 15 0 30 0 0 15 MAX ns ns ns ns ns ns ns ns ns ns STK25C48-20 STK25C48-25
(VCC = 5.0V 10%)b
STK25C48-35 STK25C48-45 UNITS
Note j: Note k:
If W is low when E goes low, the outputs remain in the high-impedance state. E or W must be VIH during address transitions.
SRAM WRITE CYCLE #1: W Controlledk
tAVAV ADDRESS tELWH E
14 19 12
tWHAX
tAVWH
18 tAVWL 13
17
W
tWLWH
15 16
tDVWH DATA IN tWLQZ DATA OUT
PREVIOUS DATA HIGH IMPEDANCE 20 DATA VALID
tWHDX
tWHQX
21
SRAM WRITE CYCLE #2: E Controlledk
tAVAV ADDRESS tAVEL E
18 1 4 19 12
tELEH
tEHAX
tAVEH W tWLEH
16 13
17
tDVEH DATA IN DATA OUT
HIGH IMPEDANCE DATA VALID
15
tEHDX
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STK25C48
AutoStoreTM/POWER-UP RECALL
SYMBOLS NO. Standard 22 23 24 25 26 tRESTORE tSTORE tDELAY VSWITCH VRESET Power-up RECALL Duration STORE Cycle Duration Time Allowed to Complete SRAM Cycle Low Voltage Trigger Level Low Voltage Reset Level 1 4.0 4.5 3.6 PARAMETER MIN MAX 550 10 s ms s V V f l h h
(VCC = 5.0V 10%)b
STK25C48 UNITS NOTES
Note l:
tRESTORE starts from the time VCC rises above VSWITCH.
AutoStoreTM/POWER-UP RECALL
VCC
5V 25 VSWITCH 26 VRESET
AutoStoreTM
23 tSTORE
OWER-UP RECALL 22 tRESTORE W DQ (DATA OUT)
24 tDELAY
POWER-UP RECALL
BROWN OUT NO STORE DUE TO NO SRAM WRITES NO RECALL (VCC DID NOT GO BELOW VRESET)
BROWN OUT AutoStoreTM NO RECALL (VCC DID NOT GO BELOW VRESET)
BROWN OUT AutoStoreTM RECALL WHEN VCC RETURNS ABOVE VSWITCH
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STK25C48
DEVICE OPERATION
The STK25C48 is a versatile memory chip that provides several modes of operation. The STK25C48 can operate as a standard 8K x 8 SRAM. It has an 8K x 8 EEPROM shadow to which the SRAM information can be copied, or from which the SRAM can be updated in nonvolatile mode.
AutoStoreTM OPERATION
The STK25C48 uses the intrinsic system capacitance to perform an automatic store on power down. As long as the system power supply takes at least tSTORE to decay from VSWITCH down to 3.6V, the STK25C48 will safely and automatically store the SRAM data in EEPROM on power down. In order to prevent unneeded STORE operations, automatic STORE will be ignored unless at least one WRITE operation has taken place since the most recent STORE or RECALL cycle.
NOISE CONSIDERATIONS
Note that the STK25C48 is a high-speed memory and so must have a high-frequency bypass capacitor of approximately 0.1F connected between VCC and VSS, using leads and traces that are as short as possible. As with all high-speed CMOS ICs, normal careful routing of power, ground and signals will help prevent noise problems.
POWER-UP RECALL
During power up, or after any low-power condition (VCC < VRESET), an internal RECALL request will be latched. When VCC once again exceeds the sense voltage of VSWITCH, a RECALL cycle will automatically be initiated and will take tRESTORE to complete. If the STK25C48 is in a WRITE state at the end of power-up RECALL, the SRAM data will be corrupted. To help avoid this situation, a 10K Ohm resistor should be connected either between W and system VCC or between E and system VCC.
SRAM READ
The STK25C48 performs a READ cycle whenever E and G are low and W is high. The address specified on pins A0-10 determines which of the 2,048 data bytes will be accessed. When the READ is initiated by an address transition, the outputs will be valid after a delay of tAVQV (READ cycle #1). If the READ is initiated by E or G, the outputs will be valid at tELQV or at tGLQV, whichever is later (READ cycle #2). The data outputs will repeatedly respond to address changes within the tAVQV access time without the need for transitions on any control input pins, and will remain valid until another address change or until E or G is brought high or W is brought low.
HARDWARE PROTECT
The STK25C48 offers hardware protection against inadvertent STORE operation and SRAM WRITEs during low-voltage conditions. When VCC < VSWITCH, STORE operations and SRAM WRITEs are inhibited.
SRAM WRITE
A WRITE cycle is performed whenever E and W are low. The address inputs must be stable prior to entering the WRITE cycle and must remain stable until either E or W goes high at the end of the cycle. The data on the common I/O pins DQ0-7 will be written into the memory if it is valid tDVWH before the end of a W controlled WRITE or tDVEH before the end of an E controlled WRITE. It is recommended that G be kept high during the entire WRITE cycle to avoid data bus contention on the common I/O lines. If G is left low, internal circuitry will turn off the output buffers tWLQZ after W goes low.
LOW AVERAGE ACTIVE POWER
The STK25C48 draws significantly less current when it is cycled at times longer than 50ns. Figure 2 shows the relationship between ICC and READ cycle time. Worst-case current consumption is shown for both CMOS and TTL input levels (commercial temperature range, VCC = 5.5V, 100% duty cycle on chip enable). Figure 3 shows the same relationship for WRITE cycles. If the chip enable duty cycle is less than 100%, only standby current is drawn when the chip is disabled. The overall average current drawn by the STK25C48 depends on the following items: 1) CMOS vs. TTL input levels; 2) the duty cycle of chip enable; 3) the overall cycle rate for accesses; 4) the ratio of READs to WRITEs; 5) the operating temperature; 6) the VCC level; and 7) I/O loading.
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STK25C48
100 100
Average Active Current (mA)
80
Average Active Current (mA)
80
60
60 TTL CMOS 20
40 TTL 20 CMOS 0 50 100 150 Cycle Time (ns) 200
40
0 50 100 150 Cycle Time (ns) 200
Figure 2: ICC (max) Reads
Figure 3: ICC (max) Writes
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STK25C48 ORDERING INFORMATION
STK25C48 - W 25 I Temperature Range
Blank = Commercial (0 to 70C) I = Industrial (-40 to 85C)
Access Time
20 = 20ns (Commercial only) 25 = 25ns 35 = 35ns 45 = 45ns
Package
W = Plastic 24-pin 600 mil DIP
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