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HMT425S6MFR6A Datasheet, PDF (17/53 Pages) Hynix Semiconductor – DDR3L SDRAM Unbuffered SODIMMs Based on 4Gb M-die
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Vref Tolerances
The dc-tolerance limits and ac-noise limits for the reference voltages VRefCA and VRefDQ are illustrated in
figure below. It shows a valid reference voltage VRef (t) as a function of time. (VRef stands for VRefCA and
VRefDQ likewise).
VRef (DC) is the linear average of VRef (t) over a very long period of time (e.g. 1 sec). This average has to
meet the min/max requirements in the table "Differential Input Slew Rate Definition" on page 23. Further-
more VRef (t) may temporarily deviate from VRef (DC) by no more than +/- 1% VDD.
voltage
VDD
VRef(DC)
VRef ac-noise
VRef(t)
VRef(DC)max
VDD/2
VRef(DC)min
VSS
time
Illustration of VRef(DC) tolerance and VRef ac-noise limits
The voltage levels for setup and hold time measurements VIH(AC), VIH(DC), VIL(AC), and VIL(DC) are depen-
dent on VRef.
“VRef” shall be understood as VRef(DC), as defined in figure above.
This clarifies that dc-variations of VRef affect the absolute voltage a signal has to reach to achieve a valid
high or low level and therefore the time to which setup and hold is measured. System timing and voltage
budgets need to account for VRef(DC) deviations from the optimum position within the data-eye of the input
signals.
This also clarifies that the DRAM setup/hold specification and derating values need to include time and
voltage associated with VRefac-noise. Timing and voltage effects due to ac-noise on VRef up to the speci-
fied limit (+/- 1% of VDD) are included in DRAM timings and their associated deratings.
Rev. 1.0 / Jul. 2012
17
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