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W3EG7264S-JD3 Datasheet(PDF) 9 Page - White Electronic Designs Corporation |
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W3EG7264S-JD3 Datasheet(HTML) 9 Page - White Electronic Designs Corporation |
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9 / 11 page  9 White Electronic Designs Corporation • (602) 437-1520 • www.wedc.com White Electronic Designs May 2005 Rev. 5 W3EG7264S-JD3-D3 PRELIMINARY 11. It is recommended that DQS be valid (HIGH or LOW) on or before the WRITE command. The case shown (DQS going from High-Z to logic LOW) applies when no WRITEs were previously in progress on the bus. If a previous WRITE was in progress, DQS could be high during this time, depending on tDQSS. 12. The refresh period is 64ms. This equates to an average refresh rate of 7.8125µs. However, an AUTO REFRESH command must be asserted at least once every 70.3µs; burst refreshing or posting by the DRAM controller greater than eight refresh cycles is not allowed. 13. The valid data window is derived by achieving other specifications - tHP (tCK/2), tDQSQ, and tQH (tQH = tHP - tQHS). The data valid window derates directly proportional with the clock duty cycle and a practical data valid window can be derived. The clock is allowed a maximum duty cycled variation of 45/55. Functionality is uncertain when operating beyond a 45/55 ratio. The data valid window derating curves are provided below for duty cycles ranging between 50/50 and 45/55. 14. Referenced to each output group: x8 = DQS with DQ0-DQ7. 15. READs and WRITEs with auto precharge are not allowed to be issued until tRAS (MIN) can be satisfied prior to the internal precharge command being issued. 16. JEDEC specifies CK and CK# input slew rate must be > 1V/ns (2V/ns differentially). 17. DQ and DM input slew rates must not deviate from DQS by more than 10%. If the DQ/DM/DQS slew rate is less than 0.5V/ns, timing must be derated: 50ps must be added to tDS and tDH for each 100mV/ns reduction in slew rate. If slew rates exceed 4V/ns, functionality is uncertain. 18. tHP min is the lesser of tCL min and tCH min actually applied to the device CK and CK# inputs, collectively during bank active. 19. tHZ (MAX) will prevail over the tDQSCK (MAX) + tRPST (MAX) condition. tLZ (MIN) will prevail over tDQSCK (MIN) + PRE (MAX) condition. 20. For slew rates greater than 1V/ns the (LZ) transition will start about 310ps earlier. 21. CKE must be active (High) during the entire time a refresh command is executed. That is, from the time the AUTO REFRESH command is registered, CKE must be active at each rising clock edge, until tRFC has been satisfied. 22. Whenever the operating frequency is altered, not including jitter, the DLL is required to be reset. This is followed by 200 clock cycles (before READ commands). Notes 1. All voltages referenced to VSS 2. Tests for AC timing, IDD, and electrical AC and DC characteristics may be conducted at normal reference / supply voltage levels, but the related specifications and device operations are guaranteed for the full voltage range specified. 3. Outputs are measured with equivalent load: Output Output (V (VOUT OUT ) Reference Reference Point Point 50Ω 50Ω VTT TT 30pF 30pF 4. AC timing and IDD tests may use a VIL-to-VIH swing of up to 1.5V in the test environment, but input timing is still referenced to VREF (or to the crossing point for CK/CK#), and parameter specifications are guaranteed for the specified AC input levels under normal use conditions. The minimum slew rate for the input signals used to test the device is 1V/ns in the range between VIL(AC) and VIH(AC). 5. The AC and DC input level specifications are defined in the SSTL_ 2 standard (i.e., the receiver will effectively switch as a result of the signal crossing the AC input level, and will remain in that state as long as the signal does not ring back above [below] the DC input LOW [high] level). 6. For slew rates less than 1V/ns and greater than or equal to 0.5V/ ns. If the slew rate is less than 0.5V/ns, timing must be derated: tIS has an additional 50ps per each 100mV/ns reduction in slew rate from the 500mV/ns. tIH has 0ps added, that is, it remains constant. If the slew rate exceeds 4.5V/ns, functionality is uncertain. For 403 and 335, slew rates must be greater than or equal to 0.5V/ns. 7. Inputs are not recognized as valid until VREF stabilizes. Exception: during the period before VREF stabilizes, CKE ≤ 0.3 x VCCQ is recognized as LOW. 8. tHZ and tLZ transitions occur in the same access time windows as valid data transitions. These parameters are not referenced to a specific voltage level, but specify when the device output is no longer driving (HZ) and begins driving (LZ). 9. The intent of the “Don’t Care” state after completion of the postamble is the DQS-driven signal should either be HIGH, LOW, or high-Z, and that any signal transition within the input switching region must follow valid input requirements. That is, if DQS transitions HIGH (above VIHDC (MIN) then it must not transition LOW (below VIHDC) prior to tDQSH (MIN). 10. This is not a device limit. The device will operate with a negative value, but system performance could be degraded due to bus turnaround. |
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