SSTL16857

The SSTL16857 is a 14-bit SSTL_2 registered driver with differential clock inputs. Both V_CC and V_DDQ support 2.5V and 3.3V operation however. V_DDQ must not exceed V_CC. Inputs are SSTL_2 type with VREF normally at 0.5*VDDQ. The outputs support class I which can be used for standard stub-series applications or capacitive loads. Master reset (RESET) asynchronously resets all registers to zero.

The SSTL16857 is intended to be incorporated into standard DIMM (Dual In-Line Memory Module) designs defined by JEDEC, such as DDR (Double Data Rate) SDRAM or SDRAM II Memory Modules. Different from traditional SDRAM, DDR SDRAM transfers data on both clock edges (rising and falling), thus doubling the peak bus bandwidth. A DDR DRAM rated at 100 MHz will have a burst rate of 200 MHz. The modules require between 23 and 27 registered control and address lines, so two 14-bit wide devices will be used on each module. The SSTL16857 is intended to be used for SSTL_2 input and output signals.

The device data inputs consist of differential receivers. One differential input is tied to the input pin while the other is tied to a reference input pad, which is shared by all inputs.

The clock input of the SSTL16857 is fully differential to be compatible with DRAM devices that are installed on the DIMM. However, since the control inputs to the SDRAM change at only half the data rate, the device must only change state on the positive transition of the CLK signal. In order to be able to provide defined outputs from the device even before a stable clock has been supplied, the SSTL16857 must support an asynchronous input pin (reset), which when held to the LOW state will assume that all registers are reset to the LOW state and all outputs drive a LOW signal as well.