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W3EG7265S202JD3 Datasheet(PDF) 10 Page - White Electronic Designs Corporation |
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W3EG7265S202JD3 Datasheet(HTML) 10 Page - White Electronic Designs Corporation |
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10 / 12 page  10 White Electronic Designs Corporation • (602) 437-1520 • www.wedc.com White Electronic Designs W3EG7265S-JD3 January 2005 Rev. 3 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 15.625µs or 7.8125µs. However, an AUTO REFRESH command must be asserted at least once every 140.6µs or 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 exceeds 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. This maximum value is derived from the referenced test load. In practice, the values obtained in a typical terminated design may reflect up to 310ps less for tHZ (MAX) and last DVW. 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 tREF later. 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. Command/Address input slew rate = 0.5V/ns. For -75 with slew rates 1V/ns and faster, tIS and tIH are reduced to 900ps. 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. 7. Inputs are not recognized as valid until VREF stabilizes. Exception: during the period before VREF stabilizes, CKE ≤ 0.3 x VCC 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 maximum limit for this parameter is not a device limit. The device will operate with a greater value for this parameter, but system performance (bus turnaround) will degrade accordingly. 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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