HYB25D256800CT Datasheet, PDF (56/94 Pages) Infineon Technologies AG – 256 Mbit Double Data Rate SDRAM

HYB25D256[16/40/80]0C[E/C/F/T](L)
256 Mbit Double-Data-Rate SDRAM
Functional Description
3.5.5 Power-Down
Power-down is entered when CKE is registered LOW (no accesses can be 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 deactivates the input
and output buffers, excluding CK, CK and CKE. The DLL is still running in Power Down mode, so for maximum
power savings, the user has the option of disabling the DLL prior to entering Power-down. In that case, the DLL
must be enabled after exiting power-down, and 200 clock cycles must occur before a Read command can be
issued. In power-down mode, CKE Low and a stable clock signal must be maintained at the inputs of the
DDR SDRAM, and all other input signals are “Don’t Care”. However, power-down duration is limited by the refresh
requirements of the device, so in most applications, the self refresh mode is preferred over the DLL-disabled
power-down mode.
The power-down state is synchronously exited when CKE is registered HIGH (along with a NOP or Deselect
command). A valid, executable command may be applied one clock cycle later.
CK
CK
CKE
Command
t_IS
VALID
No column
access in
progress
NOP
Enter Power Down mode
(Burst Read or Write operation
must not be in progress)
Figure 31 Power Down
t_IS
NOP
Exit
power down
mode
VALID
Don’t Care
Data Sheet
56
Rev. 1.6, 2004-12