2Gb: x16, x32 Mobile LPDDR2 SDRAM S4
AC and DC Logic Input Measurement Levels for Single-Ended
Signals
V REF Tolerances
The DC tolerance limits and AC noise limits for the reference voltages V REFCA and
V REFDQ are illustrated below. This figure shows a valid reference voltage V REF (t) as a
function of time. V DD is used in place of V DDCA for V REFCA , and V DDQ for V REFDQ . V REF(DC)
is the linear average of V REF (t) over a very long period of time (for example, 1 second)
and is specified as a fraction of the linear average of V DDQ or V DDCA , also over a very long
period of time (for example, 1 second). This average must meet the MIN/MAX require-
ments in Table 63 (page 119). Additionally, V REF (t) can temporarily deviate from V REF(DC)
by no more than ±1% V DD . V REF (t) cannot track noise on V DDQ or V DDCA if doing so
would force V REF outside these specifications.
Figure 82: V REF DC Tolerance and V REF AC Noise Limits
V DD
V REF(DC)
V REF(AC) noise
V REF(t)
V REF(DC)max
V DD/2
V REF(DC)min
V SS
Time
The voltage levels for setup and hold time measurements V IH(AC) , V IH(DC) , V IL(AC) , and
V IL(DC) are dependent on V REF .
V REF DC variations affect the absolute voltage a signal must reach to achieve a valid
HIGH or LOW, as well as the time from which setup and hold times are measured. When
V REF is outside the specified levels, devices will function correctly with appropriate tim-
ing deratings as long as:
? V REF is maintained between 0.44 x V DDQ (or V DDCA ) and 0.56 x V DDQ (or V DDCA ), and
? the controller achieves the required single-ended AC and DC input levels from instan-
taneous V REF (see Table 63 (page 119)).
System timing and voltage budgets must account for V REF deviations outside this range.
The setup/hold specification and derating values must include time and voltage associ-
ated with V REF AC noise. Timing and voltage effects due to AC noise on V REF up to the
specified limit (±1% V DD ) are included in LPDDR2 timings and their associated derat-
ings.
PDF: 09005aef83f3f2eb
2gb_mobile_lpddr2_s4_g69a.pdf – Rev. N 3/12 EN
120
Micron Technology, Inc. reserves the right to change products or specifications without notice.
2010 Micron Technology, Inc. All rights reserved.
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