This 11-bit bus switch is designed for 1.7 V to 1.9 V VDD operation and SSTL_18 select
Each Host port pin (HPn) is multiplexed to one of four DIMM port pins (xDPn). The
selection of the DIMM port to be connected to the Host port is controlled by a decoder
driven by three hardware select pins S0, S1 and EN. Driving pin EN HIGH disconnects all
DIMM ports from their respective host ports. When EN is driven LOW, pins S0 and S1
select one of four DIMM ports to be connected to their respective host port. When
disconnected, any DIMM port is terminated to the externally supplied voltage Vbias by
means of an on-chip pull-down resistor of typically 400 Ω. The ON-state connects the
Host port to the DIMM port through a 12 Ω nominal series resistance. The design is
intended to have only one DIMM port active at any time.
The CBTU4411 can also be configured to support a differential strobe signal on
channel 10 (TRUE) and channel 9 (complementary Strobe). When its LVCMOS
configuration input strobe enable (STREN) is HIGH, channel 10 is pulled up to 3/4 of VDD
internally by a resistive divider when the DIMM port is idle. When the CBTU4411 is
disabled (EN = HIGH in Strobe mode), the pull-down on channel 10 is disabled for current
savings, pulling channel 10 to VDD. When strobe enable (STREN) is LOW, channel 10
behaves the same as all other channels.
The select inputs (S0, S1) are pseudo-differential type SSTL_18. A reference voltage
should be provided to input pin VREF at nominally 0.5VDD. This topology provides
accurate control of switching times by reducing dependency on select signal slew rates.
S0 and S1 are provided with selectable input termination to 0.5VDD (active when LVCMOS
input TERM is HIGH). When the CBTU4411 is disabled (EN = HIGH), both S0 and S1
inputs are pulled LOW.
The part incorporates a very low crosstalk design. It has a very low skew between outputs
(< 30 ps) and low skew (< 30 ps) for rising and falling edges. The part has optimal
performance in DDR2 data bus applications.
Each switch has been optimized for connection to 1- or 2-rank DIMMs.
The low internal RC time constant of the switch allows data transfer to be made with
minimal propagation delay.
The CBTU4411 is characterized for operation from 0 °C to +85 °C.