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Power-Down Mode
DDR2 SDRAM supports multiple power-down modes that allow significant power sav-
ings over normal operating modes. CKE is used to enter and exit different power-down
DDR2 SDRAM requires CKE to be registered HIGH (active) at all times that an access is
in progress—from the issuing of a READ or WRITE command until completion of the
burst. Thus, a clock suspend is not supported. For READs, a burst completion is defined
when the read postamble is satisfied; for WRITEs, a burst completion is defined when
the write postamble and tWR (WRITE-to-PRECHARGE command) or tWTR (WRITE-to-
is either two or tWTR/tCK, whichever is greater.
coincident with an NOP or DESELECT command. CKE is not allowed to go LOW during
a mode register or extended mode register command time, or while a READ or WRITE
operation is in progress. If power-down occurs when all banks are idle, this mode is
referred to as precharge power-down. If power-down occurs when there is a row active
in any bank, this mode is referred to as active power-down. Entering power-down deac-
tivates the input and output buffers, excluding CK, CK#, ODT, and CKE. For maximum
power savings, the DLL is frozen during precharge power-down. Exiting active power-
down requires the device to be at the same voltage and frequency as when it entered
power-down. Exiting precharge power-down requires the device to be at the same volt-
age as when it entered power-down; however, the clock frequency is allowed to change
The maximum duration for either active or precharge power-down is limited by the re-
fresh requirements of the device tRFC (MAX). The minimum duration for power-down
entry and exit is limited by the tCKE (MIN) parameter. The following must be main-
tained while in power-down mode: CKE LOW, a stable clock signal, and stable power
supply signals at the inputs of the DDR2 SDRAM. All other input signals are “Don’t
Care” except ODT. Detailed ODT timing diagrams for different power-down modes are
The power-down state is synchronously exited when CKE is registered HIGH (in con-
1Gb: x4, x8, x16 1.55V DDR2 SDRAM
Power-Down Mode
PDF: 09005aef82b91d01
1GbDDR2_1_55V.PDF Rev. A 5/09 EN
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