S75WS256NDFBAWMB datasheet(158/216 Pages) SPANSION

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S75WS256Nxx Based MCPs

S75WS-N-00_A0 February 17, 2005

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Inf o rmation

30 Low-Power Operation

30.1 Standby Mode Operation

During standby, the device current consumption is reduced to the level necessary to perform the

DRAM refresh operation. Standby operation occurs when CE# is High.

The device will enter a reduced power state upon completion of a Read or Write operation, or

when the address and control inputs remain static for an extended period of time. This mode will

continue until a change occurs to the address or control inputs.

30.2 Temperature Compensated Refresh

Temperature compensated refresh (TCR) is used to adjust the refresh rate depending on the de-

vice operating temperature. DRAM technology requires increasingly frequent refresh operation to

maintain data integrity as temperatures increase. More frequent refresh is required due to in-

creased leakage of the DRAM capacitive storage elements as temperatures rise. A decreased

refresh rate at lower temperatures will facilitate a savings in standby current.

TCR allows for adequate refresh at four different temperature thresholds (+15

°C, +45°C, +70°C,

and +85

°C). The setting selected must be for a temperature higher than the case temperature

of the CellularRAM device. For example, if the case temperature is 50

°C, the system can minimize

self refresh current consumption by selecting the +7

°0C setting. The +15°C and +45°C settings

would result in inadequate refreshing and cause data corruption.

30.3 Partial Array Refresh

Partial array refresh (PAR) restricts refresh operation to a portion of the total memory array. This

feature enables the device to reduce standby current by refreshing only that part of the memory

array required by the host system. The refresh options are full array, one-half array, one-quarter

array, three-quarter array, or none of the array. The mapping of these partitions can start at either

the beginning or the end of the address map (Table 31.6). Read and Write operations to address

ranges receiving refresh will not be affected. Data stored in addresses not receiving refresh will

become corrupted. When re-enabling additional portions of the array, the new portions are avail-

able immediately upon writing to the RCR.

30.4 Deep Power-Down Operation

Deep power-down (DPD) operation disables all refresh-related activity. This mode is used if the

system does not require the storage provided by the CellularRAM device. Any stored data will be-

come corrupted when DPD is enabled. When refresh activity has been re-enabled by rewriting the

RCR, the CellularRAM device will require 150µs to perform an initialization procedure before nor-

mal operations can resume. During this 150µs period, the current consumption will be higher than

the specified standby levels, but considerably lower than the active current specification.

DPD cannot be enabled or disabled by writing to the RCR using the software access sequence;

the RCR should be accessed using CRE instead.

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