NT5CB128M16IP-EKB datasheet(42/162 Pages) NANYA

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Version 2.1

Nanya Technology Cooperation ©

07/2017

NTC Proprietary

Level: Property

DDR3(L) 2Gb SDRAM

NT5CB(C)256M8IN / NT5CB(C)128M16IP

Write Leveling

For better signal integrity, DDR3(L) memory adopted fly by topology for the commands, addresses, control signals, and

clocks. The fly by topology has benefits from reducing number of stubs and their length but in other aspect, causes flight

time skew between clock and strobe at every DRAM on DIMM. It makes it difficult for the Controller to maintain tDQSS,

tDSS, and tDSH specification. Therefore, the controller should supp

ort “write leveling” in DDR3(L) SDRAM to compensate

the skew.

The memory controller can use the “write leveling” feature and feedback from the DDR3(L) SDRAM to adjust the DQS -

 to CK -  relationship. The memory controller involved in the leveling must have adjustable delay setting on DQS -

 to align the rising edge of DQS -  with that of the clock at the DRAM pin. DRAM asynchronously feeds back CK -

, sampled with the rising edge of DQS - , through the DQ bus. The controller repeatedly delays DQS - until a

transition from 0 to 1 is detected. The DQS -

 delay established though this exercise would ensure tDQSS specification.

Besides tDQSS, tDSS, and tDSH specification also needs to be fulfilled. One way to achieve this is to combine the actual

tDQSS in the application with an appropriate duty cycle and jitter on the DQS-

signals. Depending on the actual

tDQSS in the application, the actual values for tDQSL and tDQSH may have to be better than the absolute limits provided in

“AC Timing Parameters” section in order to satisfy tDSS and tDSH specification. A conceptual timing of this scheme is

show as below figure.

Write Leveling Concept

0 or 1

Diff_CK

Diff _ DQS

Source

Diff _CK

Diff_DQS

Destination

Push DQS to capture

0 -1

transition

0 or 1

DQS/

 driven by the controller during leveling mode must be determined by the DRAM based on ranks populated.

Similarly, the DQ bus driven by the DRAM must also be terminated at the controller.

A separated feedback mechanism should be able for each byte lane. The low byte lane

’s prime DQ, DQ0, carries the

leveling feedback to the controller across the DRAM configurations x4/x8 whereas DQ0 indicates the lower diff_DQS

(diff_LDQS) to clock relationship. The high byte lane

’s prime DQ, DQ8, provides the feedback of the upper diff_DQS

(diff_UDQS) to clock relationship

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