74SSTUB32868ZRHR by Texas Instruments | Registers & Registered Buffers | Avnet AMERICAS
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74SSTUB32868ZRHR

Texas Instruments

Registered Buffer Single 28-CH CMOS 176-Pin NFBGA T/R

Manufacturer Part #: 74SSTUB32868ZRHR

Avnet Manufacturer Part #: 74SSTUB32868ZRHR


RoHS Compliant

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This 28-bit 1:2 configurable registered buffer is designed for 1.7-V to 1.9-V VCC operation. One device per DIMM is required to drive up to 18 SDRAM loads or two devices per DIMM are required to drive up to 36 SDRAM loads.

All inputs are SSTL_18, except the chip-select gate-enable (CSGEN), control (C), and reset (RESET) inputs, which are LVCMOS. All outputs are edge-controlled circuits optimized for unterminated DIMM loads, and meet SSTL_18 specifications, except the open-drain error (QERR\) output.

The 74SSTUB32868 operates from a differential clock (CLK and CLK). Data are registered at the crossing of CLK going high and CLK going low.

The 74SSTUB32868 accepts a parity bit from the memory controller on the parity bit (PAR_IN) input, compares it with the data received on the DIMM-independent D-inputs (D1-D5, D7, D9-D12, D17-D28 when C = 0; or D1-D12, D17-D20, D22, D24-D28 when C = 1) and indicates whether a parity error has occurred on the open-drain QERR \pin (active low). The convention is even parity, i.e., valid parity is defined as an even number of ones across the DIMM-independent data inputs combined with the parity input bit. To calculate parity, all DIMM-independent D-inputs must be tied to a known logic state.

The 74SSTUB32868 includes a parity checking function. Parity, which arrives one cycle after the data input to which it applies, is checked on the PAR_IN input of the device. Two clock cycles after the data are registered, the corresponding QERR signal is generated.

If an error occurs and the QERR\ output is driven low, it stays latched low for a minimum of two clock cycles or until RESET \is driven low. If two or more consecutive parity errors occur, the QERR\ output is driven low and latched low for a clock duration equal to the parity error duration or until RESET is driven low. If a parity error occurs on the clock cycle before the device enters the low-power mode (LPM) and the QERR\ output is driven low, it stays latched low for the LPM duration plus two clock cycles or until RESET is driven low. The DIMM-dependent signals (DCKE0, DCKE1, DODT0, DODT1, DCS0\ and DCS1\) are not included in the parity check computation.

The C input controls the pinout configuration from register-A configuration (when low) to register-B configuration (when high). The C input should not be switched during normal operation. It should be hard-wired to a valid low or high level to configure the register in the desired mode.

In the DDR2 RDIMM application, RESET is specified to be completely asynchronous with respect to CLK and CLK. Therefore, no timing relationship can be ensured between the two. When entering reset, the register is cleared and the data outputs is driven low quickly, relative to the time to disable the differential input receivers. However, when coming out of reset, the registerbecomes active quickly, relative to the time to enable the differential input receivers. As long as the data inputs are low, and the clock is stable during the time from the low-to-high transition of RESET until the input receivers are fully enabled, the design of the 74SSTUB32868 must ensure that the outputs remain low, thus ensuring no glitches on the output.

Key Features

  • Member of the Texas Instruments Widebus+™ Family
  • Pinout Optimizes DDR2 DIMM PCB Layout
  • 1-to-2 Outputs Supports Stacked DDR2 DIMMs
  • OneDevice Per DIMM Required
  • Chip-Select Inputs Gate the Data Outputs from Changing State and Minimizes System Power Consumption
  • Output Edge-Control Circuitry Minimizes Switching Noise in an Unterminated Line
  • Supports SSTL_18 Data Inputs
  • Differential Clock (CLK and CLK) Inputs
  • Supports LVCMOS Switching Levels on the Chip-Select Gate-Enable, Control, and RESET Inputs
  • Checks Parity on DIMM-Independent Data Inputs
  • Supports Industrial Temperature Range (-40°C to 85°C)
  • RESET Input Disables Differential Input Receivers, Resets All Registers, and Forces All Outputs Low, Except QERR
  • APPLICATIONS
    • DDR2 registered DIMM
  • Technical Attributes

    Description
    Value
    Find similar Parts
    Logic Function
    Registered Buffer
    Number of Element Inputs
    28
    MSL Level
    3
    Screening Level
    Industrial
    Triggering Type
    Positive-Edge/Negative-Edge
    Maximum Propagation Delay Time @ Maximum CL
    1@1.8V ns
    Supplier Package
    NFBGA
    Polarity
    Inverting/Non-Inverting
    Maximum Operating Supply Voltage
    1.9 V
    Number of Channels per Chip
    28
    Maximum High Level Output Current
    -8 mA
    Output Signal Type
    Single-Ended
    Product Dimensions
    15 x 6 x 1.5 mm
    Maximum Frequency
    410 MHz
    Number of Element Outputs
    56
    Maximum Low Level Output Current
    8 mA
    Bus Hold
    No
    Typical Operating Supply Voltage
    1.8 V
    Number of Selection Inputs per Element
    1
    Max Processing Temp
    260
    Mounting
    Surface Mount
    Reset Type
    Asynchronous
    Number of Elements per Chip
    1
    Fabrication Technology
    CMOS
    Minimum Operating Supply Voltage
    1.7 V
    Lead Finish
    Tin/Silver/Copper
    Pin Count
    176
    Operating Temperature
    -40 to 85 °C
    Propagation Delay Test Condition
    30 pF
    Input Signal Type
    Single-Ended

    ECCN / UNSPSC

    Description
    Value
    ECCN:
    EAR99
    SCHEDULE B:
    8542390000

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