MT40A512M8RH-075E Datasheet, PDF (149/365 Pages) Micron Technology – DDR4 SDRAM

4Gb: x4, x8, x16 DDR4 SDRAM
SELF REFRESH Operation
SELF REFRESH Operation
The SELF REFRESH command can be used to retain data in the device, even if the rest
of the system is powered down. When in self refresh mode, the device retains data with-
out external clocking. The device has a built-in timer to accommodate SELF REFRESH
operation. The SELF REFRESH command is defined by having CS_n, RAS_n, CAS_n,
and CKE held LOW with WE_n and ACT_n HIGH at the rising edge of the clock.
Before issuing the SELF REFRESH ENTRY command, the device must be idle with all
banks in the precharge state and ^tRP satisfied. Idle state is defined as: All banks are
closed (^tRP, ^tDAL, and so on, satisfied), no data bursts are in progress, CKE is HIGH, and
all timings from previous operations are satisfied (^tMRD, ^tMOD, ^tRFC, ^tZQinit, ^tZQoper,
t_{ZQCS, and so on). After the SELF REFRESH ENTRY command is registered, CKE must}
be held LOW to keep the device in self refresh mode. The DRAM automatically disables
ODT termination, regardless of the ODT pin, when it enters self refresh mode and auto-
matically enables ODT upon exiting self refresh. During normal operation (DLL_on),
the DLL is automatically disabled upon entering self refresh and is automatically ena-
bled (including a DLL reset) upon exiting self refresh.
When the device has entered self refresh mode, all of the external control signals, except
CKE and RESET_n, are “Don’t Care.” For proper SELF REFRESH operation, all power
supply and reference pins (V_DD, V_DDQ, V_SS, V_SSQ, V_PP, and V_REFCA) must be at valid levels.
The DRAM internal V_REFDQ generator circuitry may remain on or be turned off depend-
ing on the MRx bit Y setting. If the internal V _REFDQ circuit is on in self refresh, the first
WRITE operation or first write-leveling activity may occur after ^tXS time after self re-
fresh exit. If the DRAM internal V_REFDQ circuitry is turned off in self refresh, it ensures
that the V_REFDQ generator circuitry is powered up and stable within the ^tXSDLL period
when the DRAM exits the self refresh state. The first WRITE operation or first write-lev-
eling activity may not occur earlier than ^tXSDLL after exiting self refresh. The device ini-
tiates a minimum of one REFRESH command internally within the ^tCKE period once it
enters self refresh mode.
The clock is internally disabled during a SELF REFRESH operation to save power. The
minimum time that the device must remain in self refresh mode is ^tCKESR/
t_{CKESR_PAR. The user may change the external clock frequency or halt the external}
clock ^tCKSRE/^tCKSRE_PAR after self refresh entry is registered; however, the clock must
be restarted and ^tCKSRX must be stable before the device can exit SELF REFRESH oper-
ation.
The procedure for exiting self refresh requires a sequence of events. First, the clock must
be stable prior to CKE going back HIGH. Once a SELF REFRESH EXIT command (SRX,
combination of CKE going HIGH and DESELECT on the command bus) is registered,
the following timing delay must be satisfied:
Commands that do not require locked DLL:
• ^tXS = ACT, PRE, PREA, REF, SRE, and PDE.
• ^tXS_FAST = ZQCL, ZQCS, and MRS commands. For an MRS command, only DRAM
CL, WR/RTP register, and DLL reset in MR0; R_TT(NOM) register in MR1; the CWL and
R_TT(WR) registers in MR2; and gear-down mode register in MR3; WRITE and READ pre-
amble registers in MR4; R_TT(PARK) register in MR5; ^tCCD_L/^tDLLK and V_REFDQ calibra-
tion value registers in MR6 may be accessed provided the DRAM is not in per-DRAM
mode. Access to other DRAM mode registers must satisfy ^tXS timing. WRITE com-
mands (WR, WRS4, WRS8, WRA, WRAS4, and WRAS8) that require synchronous ODT
and dynamic ODT controlled by the WRITE command require a locked DLL.
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4gb_ddr4_dram.pdf - Rev. G 1/17 EN
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