W949D6DB Datasheet, PDF (44/60 Pages) Winbond – Standard Self Refresh Mode

W949D6DB / W949D2DB
8.11 Self Refresh
The SELF REFRESH command can be used to retain data in the LPDDR SDRAM, even if the rest of
the system is powered down. When in the Self Refresh mode, the LPDDR SDRAM retains data without
external clocking. The LPDDR SDRAM device has a built-in timer to accommodate Self Refresh
operation. The SELF REFRESH command is initiated like an AUTO REFRESH command except CKE
is LOW. Input signals except CKE are “Don’t Care” during Self Refresh. The user may halt the external
clock one clock after the SELF REFRESH command is registered.
Once the command is registered, CKE must be held low to keep the device in Self Refresh mode. The
clock is internally disabled during Self Refresh operation to save power. The minimum time that the
device must remain in Self Refresh mode is tRFC.
The procedure for exiting Self Refresh requires a sequence of commands. First, the clock must be stable
prior to CKE going back High. Once Self Refresh Exit is registered, a delay of at least tXSR must be
satisfied before a valid command can be issued to the device to allow for completion of any internal
refresh in progress.
The use of Self Refresh mode introduces the possibility that an internally timed refresh event can be
missed when CKE is raised for exit from Self Refresh mode. Upon exit from Self Refresh an extra AUTO
REFRESH command is recommended.
In the Self Refresh mode, Partial Array Self Refresh (PASR) function is described in the Extended Mode
Register section.
8.11.1 Self Refresh Command
CK
CK
CKE
CS
RAS
CAS
WE
A0-An
BA0,BA1
= Don't Care
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Publication Release Date: Oct. 08, 2014
Revision: A01-003