K7I643684M Datasheet, PDF (7/18 Pages) Samsung semiconductor – 72Mb DDRII SRAM Specification

K7I643684M
K7I641884M
2Mx36 & 4Mx18 DDRII CIO b4 SRAM
Depth Expansion
Separate input and output ports enables easy depth expansion.
Each port can be selected and deselected independently and read and write operation do not affect each other.
Before chip deselected, all read and write pending operations are completed.
Programmable Impedance Output Buffer Operation
The designer can program the SRAM's output buffer impedance by terminating the ZQ pin to VSS through a precision resistor(RQ).
The value of RQ (within 15%) is five times the output impedance desired.
For example, 250Ω resistor will give an output impedance of 50Ω.
Impedance updates occur early in cycles that do not activate the outputs, such as deselect cycles.
In all cases impedance updates are transparent to the user and do not produce access time "push-outs" or other anomalous
behavior in the SRAM.
There are no power up requirements for the SRAM. However, to guarantee optimum output driver impedance after power up, the
SRAM needs 1024 non-read cycles.
Echo clock operation
To assure the output traceability, the SRAM provides the output Echo clock, pair of compliment clock CQ and CQ,
which are synchronized with internal data output.
Echo clocks run free during normal operation.
The Echo clock is triggered by internal output clock signal, and transferred to external through same structures as output driver.
Clock Consideration
K7I643684M and K7I641884M utilizes internal DLL(Delay-Locked Loops) for maximum output data valid window.
It can be placed into a stopped-clock state to minimize power with a modest restart time of 1024 clock cycles.
Circuitry automatically resets the DLL when absence of input clock is detected.
Power-Up/Power-Down Supply Voltage Sequencing
The following power-up supply voltage application is recommended: VSS, VDD, VDDQ, VREF, then VIN. VDD and VDDQ can be applied
simultaneously, as long as VDDQ does not exceed VDD by more than 0.5V during power-up. The following power-down supply voltage
removal sequence is recommended: VIN, VREF, VDDQ, VDD, VSS. VDD and VDDQ can be removed simultaneously, as long as VDDQ
does not exceed VDD by more than 0.5V during power-down.
Rev. 1.3 March 2007
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