DRA790 Datasheet, PDF (406/436 Pages) Texas Instruments – Infotainment Applications Processor

DRA790, DRA791
DRA793, DRA797
SPRS968A – AUGUST 2016 – REVISED FEBRUARY 2017
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7.7.2.4.2 16-Bit DDR3 Interface
Note that the 16-bit wide interface schematic is practically identical to the 32-bit interface (see Figure 7-38
and Figure 7-39); only the high-word DDR memories are removed and the unused DQS inputs are tied off.
When not using all or part of a DDR interface, the proper method of handling the unused pins is to tie off
the ddrx_dqsi pins to ground via a 1k-Ω resistor and to tie off the ddrx_dqsni pins to the corresponding
vdds_ddrx supply via a 1k-Ω resistor. This needs to be done for each byte not used. Although these
signals have internal pullups and pulldowns, external pullups and pulldowns provide additional protection
against external electrical noise causing activity on the signals.
The vdds_ddrx and ddrx_vref0 power supply pins need to be connected to their respective power supplies
even if ddrx is not being used. All other DDR interface pins can be left unconnected. Note that the
supported modes for use of the DDR EMIF are 32-bits wide, 16-bits wide, or not used.
406 Applications, Implementation, and Layout
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