IS43LD16640C datasheet(73/142 Pages) ISSI

73 / 142 page

IS43/46LD16640C

IS43/46LD32320C

Integrated Silicon Solution, Inc. — www.issi.com

Rev. C

07/02/2021

® Long-term Support

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MRW RESET Command

The MRW RESET command brings the device to the device auto initialization (resetting) state in

the power-on initialization sequence (see RESET Command under Power-Up ). The MRW RESET

command can be issued from the idle state. This command resets all mode registers to their de-

fault values. Only the NOP command is supported during tINIT4. After MRW RESET, boot timings

must be observed until the

device initialization sequence is complete and the device is in the idle state. Array data is unde-

fined after the MRW RESET command has completed.

For MRW RESET timing, see Figure of Voltage Ramp and Initialization Sequence.

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 support ZQ calibration.

To achieve tighter tolerances, proper ZQ calibration must be performed.

There are four ZQ calibration commands and related timings: tZQINIT, tZQRESET, tZQCL, and

tZQCS. tZQINIT is used for initialization calibration; tZQRESET is used for resetting ZQ to the

default output impedance; tZQCL is used for long calibration(s); and tZQCS 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 impedance 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 periodi-

cally 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 impedance

errors within tZQCS for all speed bins, assuming the maximum sensitivities specified in the tables

"output Driver Sensitivity Definition" and "Output Driver Temperature and Voltage Sensitivity" (page

133) are met. The appropriate interval between ZQCS commands can be determined using these

tables and system-specific parameters.

LPDDR2 devices are subject to temperature drift rate (Tdriftrate) and voltage drift rate (Vdriftrate)

in various applications. To accommodate drift rates and calculate the necessary interval between

ZQCS commands, apply the following formula.

ZQcorrection / 〔(Tsens × Tdriftrate) + (Vsens × Vdriftrate)〔

Where Tsens = MAX (dRONdT) and Vsens = MAX (dRONdV) define temperature and voltage

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