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GS81332QT37CE-350M Fiches technique(PDF) 11 Page - GSI Technology |
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GS81332QT37CE-350M Fiches technique(HTML) 11 Page - GSI Technology |
11 / 30 page GS82612QT19/37CE-350M/250M GS81332QT19/37CE-350M/250M GS8692QT19/37CE-350M/250M Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com. Rev: 1.01 7/2017 11/30 © 2017, GSI Technology Preliminary FLXDrive-II Output Driver Impedance Control HSTL I/O SigmaQuad-II+ SRAMs are supplied with programmable impedance output drivers. The ZQ pin must be connected to VSS via an external resistor, RQ, to allow the SRAM to monitor and adjust its output driver impedance. The value of RQ must be 5X the value of the desired RAM output impedance. The allowable range of RQ to guarantee impedance matching continuously is between 175 and 350. Periodic readjustment of the output driver impedance is necessary as the impedance is affected by drifts in supply voltage and temperature. The SRAM’s output impedance circuitry compensates for drifts in supply voltage and temperature. A clock cycle counter periodically triggers an impedance evaluation, resets and counts again. Each impedance evaluation may move the output driver impedance level one step at a time towards the optimum level. The output driver is implemented with discrete binary weighted impedance steps. Input Termination Impedance Control These SigmaQuad-II+ SRAMs are supplied with programmable input termination on Data (D), Byte Write (BW), and Clock (K,K) input receivers. The input termination is always enabled, and the impedance is programmed via the same RQ resistor (connected between the ZQ pin and VSS) used to program output driver impedance, in conjuction with the ODT pin (6R). When the ODT pin is tied Low, input termination is "strong" (i.e., low impedance), and is nominally equal to RQ*0.3 Thevenin-equivalent when RQ is between 175Ω and 350Ω. When the ODT pin is tied High (or left floating—the pin has a small pull-up resistor), input termination is "weak" (i.e., high impedance), and is nominally equal to RQ*0.6 Thevenin-equivalent when RQ is between 175Ω and 250Ω. Periodic readjustment of the termination impedance occurs to compensate for drifts in supply voltage and temperature, in the same manner as for driver impedance (see above). Note: D, BW, K, K inputs should always be driven High or Low; they should never be tri-stated (i.e., in a High-Z state). If the inputs are tri-stated, the input termination will pull the signal to VDDQ/2 (i.e., to the switch point of the diff-amp receiver), which could cause the receiver to enter a meta-stable state, resulting in the receiver consuming more power than it normally would. This could result in the device’s operating currents being higher. Power-Up Initialization After power-up, stable input clocks must be applied to the device for 20 s prior to issuing read and write commands. See the tKInit timing parameter in the AC Electrical Characteristics section. Note: The tKInit requirement is independent of the tLock requirement, which specifies how many cycles of stable input clocks (2048) must be applied after the Doff pin has been driven High in order to ensure that the DLL locks properly (and the DLL must lock properly before issuing read and write commands). However, tKInit is greater than tKLock, even at the slowest permitted cycle time of 8.4 ns (2048*8.4 ns = 17.2 s). Consequently, the 20 s associated with tKInit is sufficient to cover the tKLock requirement at power-up if the Doff pin is driven High prior to the start of the 20 s period. Also, tKInit only needs to be met once, immediately after power-up, whereas tKLock must be met any time the DLL is disabled/reset (whether by toggling Doff Low or by stopping K clocks for > 30 ns). |
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