SN74SSQE32882

This JEDEC SSTE32882-compliant, 28-bit 1:2 or 26-bit 1:2 and 4-bit 1:1 registering clock driver with parity is designed for operation on DDR3 Registered DIMMs up to DDR3-1333 with VDD of 1.5 V.

All inputs are 1.5-V, CMOS-compatible. All outputs are 1.5-V CMOS drivers optimized to drive DRAM signals on terminated traces in DDR3 RDIMM applications. Clock outputs Yn and Yn and control net outputs DxCKEn, DxCSn, and DxODTn can each be driven with a different strength and skew to optimize signal integrity, compensate for different loading, and balance signal travel speed.

The SN74SSQE32882 has two basic modes of operation associated with the Quad Chip Select Enable (QCSEN) input.

First, when the QCSEN input pin is open or pulled high, the component has two chip select inputs, DCS0 and DCS1, and two copies of each chip select output, QACS0, QACS1, QBCS0 and QBCS1. This mode is the QuadCS disabled mode. Alternatively, when the QCSEN input pin is pulled low, the component has four chip select inputs DCS[3:0], and four chip select outputs, QCS[3:0]. This mode is the QuadCS enabled mode.

When QCSEN is high or floating, the device also supports an operating mode that allows a single device to be mounted on the back side of a DIMM array. This device can then be configured to keep the input bus termination (IBT) feature enabled for all input signals independent of MIRROR. The SN74SSQE32882. operates from a differential clock (CK and CK). Data are registered at the crossing of CK going high and CK going low. This data can either be re-driven to the outputs or used to access internal control registers. Details are covered in the Function Tables (each flip-flop) with QCSEN = low.

Input bus data integrity is protected by a parity function. All address and command input signals are summed; the last bit of the sum is then compared to the parity signal delivered by the system at the PAR_IN input one clock cycle later. If these two values do not match, the device pulls the open drain output ERROUT low. The control signals (DCKE0, DCKE1, DODT0, DODT1, and DCS[n:0]) are not part of this computation.

The SN74SSQE32882 implements different power-saving mechanisms to reduce thermal power dissipation and to support system power-down states. Power consumption is further reduced by disabling unused outputs.

The package design is optimal for high-density DIMMs. By aligning input and output positions towards DIMM finger-signal ordering and SDRAM ballout, the device de-scrambles the DIMM traces and allows low crosstalk designs with low interconnect latency. Edge-controlled outputs reduce ringing and improve signal eye opening at the SDRAM inputs.