Datasheet

Low Power Auto Self Refresh (LPASR)
DDR4 devices support Low Power Auto Self-Refresh (LPASR) operation at multiple temperatures ranges
(See temperature table below)
Auto Self Refresh (ASR)
DDR4 DRAM provides an Auto Self-Refresh mode (ASR) for application ease. ASR mode is enabled by
setting the above MR2 bits A6=1 and A7=1. The device will manage Self Refresh entry through the supported
temperature range of the DRAM. In this mode, the device will change self-refresh rate as the DRAM operating
temperature changes, lower at low temperatures and higher at high temperatures.
Manual Modes
If ASR mode is not enabled, the LPASR Mode Register must be manually programmed to one of the three
self-refresh operating modes. In this mode, the user has the flexibility to select a fixed self-refresh operating
mode at the entry of the selfrefresh according to their system memory temperature conditions. The user is
responsible to maintain the required memory temperature condition for the mode selected during the self-refresh
operation. The user may change the selected mode after exiting from self refresh and before the next self-
refresh entry. If the temperature condition is exceeded for the mode selected, there is risk to data retention
resulting in loss of data.
Table 20. Self Refresh Function table
MR2
[A7]
MR2
[A6]
LPASR Mode
Self Refresh Operation
Allowed Operating Temperature
Range for Self Refresh Mode
(all reference to DRAM T
CASE
)
0
0
Normal
Fixed normal self-Refresh rate to maintain
data retention for the normal operating
temperature. User is required to ensure
85°C DRAM T
CASE(max)
is not exceeded to
avoid any risk of data loss
(-40°C ~ 85°C)
0
1
Reduced Temperature range
Variable or fixed self-Refresh rate or any
other DRAM power consumption reduction
control for the reduced temperature range.
User is required to ensure 45°C DRAM
T
CASE(max)
is not exceeded to avoid any risk
of data loss
(-40°C ~ 45°C)
1
0
Extended Temperature range
Fixed high self-Refresh rate to optimize data
retention to support the extended temperature
range
(-40°C ~ 95°C)
1
1
Auto Self Refresh
ASR Mode Enabled. Self-Refresh power
consumption and data retention are optimized
for any given operating temperature conditions
All of the above
AS4C256M16D4
Confidential
- 45 of 201 -
Rev.1.0 Aug.2019