INMYS WIKI

LPDDR4X is a variant of LPDDR4, with the difference of additional power savings by reducing the I/O voltage from 1.1 V to 0.6 V.

ECC is supported on the LPDDR4 interface. Unlike traditional ECC interfaces which require dedicated memory pins and devices, ECC is supported inline. The ECC system impact is in interface bandwidth and overall memory density, as ECC data is stored alongside non-ECC data.

• sideband - это когда отдельный чип под ECC (для LPDDR - не бывает)
• inline - когда из разных мест читает контроллер
• on-die - когда всё в пямяти и дополнительно для ECC место выделено

• есть p\n с ECC (https://www.issi.com/WW/pdf/43-46LQ16256-32128EA-AL.pdf), есть - без ECC (https://www.issi.com/WW/pdf/43-46LQ32256A-AL.pdf)

LPDDR4 memories have software configurable on-die termination for both the data group nets. The DDR subsystem also contains software configurable on-die termination for the address/control group nets. Thus, termination is not required on any DDR signals for an LPDDR4 configuration.

LPDDR4 memories generate their own VREFCA and VREFDQ internally for the address / command bus and data bus, respectively. Similarly, the DDR PHY also provides its own reference voltage for the data group nets during reads. Thus unlike DDR3 and DDR4, VREF does not need to be generated on the board, and there is no required VREF routing for an LPDDR4 configuration.

Unlike DDR3 and DDR4, there is no required termination on the PCB of the address/control bus of an LPDDR4 configuration. All termination is handled internally (on-die). Thus, VTT does not apply for LPDDR4.

Balanced T traces (also referred to as T-branch traces) are split traces from source to multiple end points. The target impedance of the split trace should be 2 times the non-branched impedance.

The length/delay matching process should include a mechanism for compensating for the velocity delta between these two types of PCB interconnects. A compensation factor of 1.1 has been specified for this purpose by JEDEC. All microstrip segment lengths are to be divided by 1.1 before summation into the length matching equation. The resulting compensated length is termed the 'stripline equivalent length'.