IS46DR16640C datasheet(30/49 Pages) ISSI

30 / 49 page

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

Rev. 00A

6/4/2013

IS43/46DR81280C, IS43/46DR16640C

36. These parameters are specified per their average values, however it is understood that the following relationship

between the average timing and the absolute instantaneous timing holds at all times. (Min and max of SPEC values

are to be used for calculations in the table below.)

Parameter

Symbol

min

max

Units

Absolute clock period tCK(abs)

tCK(avg),min + tJIT(per),min

tCK(avg),max + tJIT(per),max

Absolute clock HIGH

pulse width

tCH(abs)

tCH(avg),min x tCK(avg),min +

tJIT(duty),min

tCH(avg),max x tCK(avg),max +

tJIT(duty),max

Absolute clock LOW

pulse width

tCL(abs)

tCL(avg),min x tCK(avg),min +

tJIT(duty),min

tCL(avg),max x tCK(avg),max +

tJIT(duty),max

Example: For DDR2-667, tCH(abs),min = ( 0.48 x 3000 ps ) - 125 ps = 1315 ps

37. tHP is the minimum of the absolute half period of the actual input clock. tHP is an input parameter but not an input

specification parameter. It is used in conjunction with tQHS to derive the DRAM output timing tQH.

The value to be used for tQH calculation is determined by the following equation;

tHP = Min ( tCH(abs), tCL(abs) ),

where,

tCH(abs) is the minimum of the actual instantaneous clock HIGH time;

tCL(abs) is the minimum of the actual instantaneous clock LOW time;

38. tQHS accounts for:

1) The pulse duration distortion of on-chip clock circuits, which represents how well the actual tHP at the input is

transferred to the output; and

2) The worst case push-out of DQS on one transition followed by the worst case pull-in of DQ on the next transition,

both of which are independent of each other, due to data pin skew, output pattern effects, and pchannel to n-channel

variation of the output drivers

39. tQH = tHP – tQHS, where:

tHP is the minimum of the absolute half period of the actual input clock; and

tQHS is the specification value under the max column.

{The less half-pulse width distortion present, the larger the tQH value is; and the larger the valid data eye will be.}

Examples:

1) If the system provides tHP of 1315 ps into a DDR2-667 SDRAM, the DRAM provides tQH of 975 ps minimum.

2) If the system provides tHP of 1420 ps into a DDR2-667 SDRAM, the DRAM provides tQH of 1080 ps minimum.

40. When the device is operated with input clock jitter, this parameter needs to be derated by the actual tERR(6-

10per) of the input clock. (output deratings are relative to the SDRAM input clock.)

For example, if the measured jitter into a DDR2-667 SDRAM has tERR(6-10per),min = - 272 ps and tERR(6-10per),

max = + 293 ps, then tDQSCK,min(derated) = tDQSCK,min - tERR(6-10per),max = - 400 ps - 293 ps = - 693 ps and

tDQSCK,max(derated) = tDQSCK,max - tERR(6-10per),min = 400 ps + 272 ps = + 672 ps. Similarly, tLZ(DQ) for

DDR2-667 derates to tLZ(DQ),min(derated) = - 900 ps - 293 ps = - 1193 ps and tLZ(DQ),max(derated) = 450 ps + 272

ps = + 722 ps. (Caution on the min/max usage!)

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