Datasheet

ZQ Calibration Commands
ZQ Calibration command is used to calibrate DRAM R
ON
& ODT values. The device needs longer time to
calibrate output driver and on-die termination circuits at initialization and relatively smaller time to perform
periodic calibrations.
ZQCL command is used to perform the initial calibration during power-up initialization sequence. This
command may be issued at any time by the controller depending on the system environment. ZQCL command
triggers the calibration engine inside the DRAM and, once calibration is achieved, the calibrated values are
transferred from the calibration engine to DRAM IO, which gets reflected as updated output driver and on-die
termination values.
The first ZQCL command issued after reset is allowed a timing period of t
ZQinit
to perform the full calibration
and the transfer of values. All other ZQCL commands except the first ZQCL command issued after reset are
allowed a timing period of t
ZQoper
.
ZQCS command is used to perform periodic calibrations to account for voltage and temperature variations.
A shorter timing window is provided to perform the calibration and transfer of values as defined by timing
parameter t
ZQCS
. One ZQCS command can effectively correct a minimum of 0.5 % (ZQ Correction) of R
ON
and
R
TT
impedance error within 128 nCK for all speed bins assuming the maximum sensitivities specified in the
Output Driver Voltage and ODT Voltage and Temperature Sensitivity tables. The appropriate interval between
ZQCS commands can be determined from these tables and other application specific parameters. One
method for calculating the interval between ZQCS commands, given the temperature (T
driftrate
) and voltage
(V
driftrate
) drift rates that the device is subject to in the application, is illustrated. The interval could be defined by
the following formula:
Where T
sens
= max (dR
TT
dT, dR
ON
dTM) and V
sens
= max (dR
TT
dV, dR
ON
dVM) define temperature and voltage
sensitivities.
For example, if T
sens
= 1.5%/°C, V
sens
= 0.15%/mV, T
driftrate
= 1°C/sec and V
driftrate
= 15mV/sec, then the interval
between ZQCS commands is calculated as:
No other activities should be performed on the DRAM channel by the controller for the duration of t
ZQinit
,
t
ZQoper,
or t
ZQCS
. The quiet time on the DRAM channel allows accurate calibration of output driver and on-die
termination values. Once DRAM calibration is achieved, the device should disable ZQ current consumption
path to reduce power.
All banks must be precharged and t
RP
met before ZQCL or ZQCS commands are issued by the controller.
See “Command Truth Table” on Section 4.1 for a description of the ZQCL and ZQCS commands.
ZQ calibration commands can also be issued in parallel to DLL lock time when coming out of self refresh.
Upon Self-Refresh exit, the device will not perform an IO calibration without an explicit ZQ calibration
command. The earliest possible time for ZQ Calibration command (short or long) after self refresh exit is t
XS
,
t
XS_Abort
/ t
XS_FAST
depending on operation mode.
In systems that share the ZQ resistor between devices, the controller must not allow any overlap of t
ZQoper
,
t
ZQinit
, or t
ZQCS
between the devices.
AS4C256M16D4
Confidential
- 59 of 201 -
Rev.1.0 Aug.2019