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2Gb: x16, x32 Mobile LPDDR2 SDRAM S4
MODE REGISTER WRITE Command
MRW ZQ Calibration Commands
The MRW command is used to initiate a ZQ calibration command that calibrates output
driver impedance across process, temperature, and voltage. LPDDR2-S4 devices sup-
port ZQ calibration. To achieve tighter tolerances, proper ZQ calibration must be per-
formed.
There are four ZQ calibration commands and related timings: t ZQINIT, t ZQRESET,
t ZQCL, and t ZQCS. t ZQINIT is used for initialization calibration; t ZQRESET is used for
resetting ZQ to the default output impedance; t ZQCL is used for long calibration(s); and
t ZQCS is used for short calibration(s). See the MR10 Calibration (MA[7:0] = 0Ah) table
for ZQ calibration command code definitions.
ZQINIT must be performed for LPDDR2 devices. ZQINIT provides an output impe-
dance accuracy of ±15%. After initialization, the ZQ calibration long (ZQCL) can be used
to recalibrate the system to an output impedance accuracy of ±15%. A ZQ calibration
short (ZQCS) can be used periodically to compensate for temperature and voltage drift
in the system.
ZQRESET resets the output impedance calibration to a default accuracy of ±30% across
process, voltage, and temperature. This command is used to ensure output impedance
accuracy to ±30% when ZQCS and ZQCL commands are not used.
One ZQCS command can effectively correct at least 1.5% (ZQ correction) of output im-
pedance errors within t ZQCS for all speed bins, assuming the maximum sensitivities
specified in Table 79 and Table 80 (page 133) are met. The appropriate interval between
ZQCS commands can be determined using these tables and system-specific parame-
ters.
Mobile LPDDR2 devices are subject to temperature drift rate (T driftrate ) and voltage drift
rate (V driftrate ) in various applications. To accommodate drift rates and calculate the
necessary interval between ZQCS commands, apply the following formula:
ZQ correction
(T sens × T driftrate ) + (V sens × V driftrate )
Where T sens = MAX (dR ON dT) and V sens = MAX (dR ON dV) define temperature and volt-
age sensitivities.
For example, if T sens = 0.75%/?C, V sens = 0.20%/mV, T driftrate = 1?C/sec, and V driftrate =
15 mV/sec, then the interval between ZQCS commands is calculated as:
1.5
(0.75 × 1) + (0.20 × 15)
= 0.4s
A ZQ calibration command can only be issued when the device is in the idle state with
all banks precharged.
No other activities can be performed on the data bus during calibration periods
( t ZQINIT, t ZQCL, or t ZQCS). The quiet time on the data bus helps to accurately calibrate
output impedance. There is no required quiet time after the ZQRESET command. If
multiple devices share a single ZQ resistor, only one device can be calibrating at any giv-
en time. After calibration is complete, the ZQ ball circuitry is disabled to reduce power
consumption.
PDF: 09005aef83f3f2eb
2gb_mobile_lpddr2_s4_g69a.pdf – Rev. N 3/12 EN
92
Micron Technology, Inc. reserves the right to change products or specifications without notice.
2010 Micron Technology, Inc. All rights reserved.
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相关代理商/技术参数
MT42L256M32D4KP-MS
制造商:Micron Technology Inc 功能描述:256MX32 LPDDR2 PLASTIC IND TEMP GREEN WFBGA 1.2V - Bulk