EDJ1108BABG, EDJ1116BABG
Auto-Refresh
The refresh command (REF) is used during normal operation of the DDR3 SDRAMs. This command is non
persistent, so it must be issued each time a refresh is required. The DDR3 SDRAM requires refresh cycles at an
average periodic interval of tREFI. When /CS, /RAS and /CAS are held low and /WE high at the rising edge of the
clock, the chip enters a refresh cycle. All banks of the SDRAM must be precharged and idle for a minimum of the
precharge time tRP(min) before the refresh command can be applied. The refresh addressing is generated by the
internal refresh controller. This makes the address bits “Don’t Care” during a refresh command. An internal address
counter supplies the addresses during the refresh cycle. No control of the external address bus is required once this
cycle has started. When the refresh cycle has completed, all banks of the SDRAM will be in the precharged (idle)
state. A delay between the refresh command and the next valid command, except NOP or DESL, must be greater
than or equal to the minimum refresh cycle time tRFC(min) as shown in the following figure. Note that the tRFC
timing parameter depends on memory density.
In general, a refresh command needs to be issued to the DDR3 SDRAM regularly every tREFI interval. To allow for
improved efficiency in scheduling and switching between tasks, some flexibility in the absolute refresh interval is
provided. A maximum of 8 refresh commands can be postponed during operation of the DDR3 SDRAM, meaning
that at no point in time more than a total of 8 refresh commands are allowed to be postponed. In case that 8 refresh
commands are postponed in a row, the resulting maximum interval between the surrounding refresh commands is
limited to 9 × tREFI. A maximum of 8 additional refresh commands can be issued in advance (“pulled in”), with each
one reducing the number of regular refresh commands required later by one. Note that pulling in more than
8 refresh commands in advance does not further reduce the number of regular refresh commands required later, so
that the resulting maximum interval between two surrounding refresh commands is limited to 9 × tREFI. At any given
time, a maximum of 16 REF commands can be issued within tREFI. Before entering self-refresh mode, all
postponed refresh commands must be executed.
T0
T1
T2
T3
/CK
CK
VIH
≥ tRP
≥ tRFC
≥ tRFC
CKE
Any
Command
PRE
NOP
REF
REF
NOP
Command
Refresh Command Timing
tREFI
9 × tRER
t
tRFC
8 × REF-Commands postponed
Postponing Refresh Command
tREFI
9 × tRER
t
tRFC
8 × REF-Commands postponed
Pulling-in Refresh Command
Data Sheet E1248E40 (Ver. 4.0)
120
ELPIDA [ ELPIDA MEMORY ]
