MT40A256M16GE-075E Datasheet, PDF (142/365 Pages) Micron Technology – Temperature controlled refresh (TCR)

4Gb: x4, x8, x16 DDR4 SDRAM
Temperature-Controlled Refresh Mode
Temperature-Controlled Refresh Mode
During normal operation, temperature-controlled refresh (TCR) mode disabled, the de-
vice must have a REFRESH command issued once every ^tREFI, except for what is al-
lowed by posting (see REFRESH Command section). This means a REFRESH command
must be issued once every 3.9μs if T_C is greater than or equal to 85°C, and once every
7.8μs if T_C is less than 85°C. This Mode is disabled setting MR4[3] = 0 while mode is ena-
bled setting MR4[3] = 1. When enabled (MR4[3] = 1), the temperature range must be se-
lected where MR4[2] = 0 enables the Normal Temperature range while MR4[2] = 1 ena-
bles the Extended Temperature range
Table 47: Normal ^tREFI Refresh (TCR Disabled)
Temperature
T_C < 45°C
45°C ≤ T_C < 85°C
85°C ≤ T_C < 95°C
Normal Temperature
External Refresh
Period
Internal Refresh
Period
Extended Temperature
External Refresh
Period
Internal Refresh
Period
7.8μs
7.8μs
N/A
3.9μs¹
3.9μs¹
Note: 1. If T_C is less than 85°C, the external refresh period can be 7.8μs instead of 3.9μs.
When TCR mode is enabled, the device will register the externally supplied REFRESH
command and adjust the internal refresh period to be longer than ^tREFI of the normal
temperature range, when allowed, by skipping REFRESH commands with the proper
gear ratio. TCR mode has two ranges to select between the normal temperature range
and the extended temperature range; the correct range must be selected so the internal
control operates correctly. The DRAM must have the correct refresh rate applied exter-
nally; the internal refresh rate is determined by the DRAM based upon the temperature.
TCR Mode – Normal Temperature Range
REFRESH commands should be issued to the device with the refresh period equal to or
shorter than ^tREFI of normal temperature range (0°C to 85°C). In this mode, the system
must guarantee that the T_C does not exceed 85°C. The device may adjust the internal
refresh period to be longer than ^tREFI of the normal temperature range by skipping ex-
ternal REFRESH commands with the proper gear ratio when T_C is below 45°C. The in-
ternal refresh period is automatically adjusted inside the DRAM, and the DRAM con-
troller does not need to provide any additional control.
TCR Mode – Extended Temperature Range
REFRESH commands should be issued to the device with the refresh period equal to or
shorter than ^tREFI of extended temperature range (85°C to 95°C). In this mode, the sys-
tem must guarantee that the T_C does not exceed 95°C. Even though the external refresh
supports the extended temperature range, the device will adjust its internal refresh peri-
od to ^tREFI of the normal temperature range by skipping external REFRESH commands
with proper gear ratio when operating in the normal temperature range (0°C to 85°C).
The device may adjust the internal refresh period to be longer than ^tREFI of the normal
temperature range by skipping external REFRESH commands with the proper gear ratio
when T_C is below 45°C. The internal refresh period is automatically adjusted inside the
DRAM, and the DRAM controller does not need to provide any additional control.
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