Datasheet

Electrical Characteristics and AC Timing
Reference Load for AC Timing and Output Slew Rate
Reference Load for AC Timing and Output Slew Rate represents the effective reference load of 50 ohms used
in defining the relevant AC timing parameters of the device as well as output slew rate measurements.
R
ON
nominal of DQ, DQS and DQS# drivers uses 34 ohms to specify the relevant AC timing paraeter values of
the device.
The maximum DC High level of Output signal = 1.0 x V
DDQ
,
The minimum DC Low level of Output signal = { 34 /( 34 + 50 ) } x V
DDQ
= 0.4 x V
DDQ
The nominal reference level of an Output signal can be approximated by the following:
The center of maximum DC High and minimum DC Low = { ( 1 + 0.4 ) / 2 } x V
DDQ
= 0.7 x V
DDQ
The actual reference level of Output signal might vary with driver Ron and reference load tolerances. Thus,
the actual reference level or midpoint of an output signal is at the widest part of the output signal’s eye. Prior
to measuring AC parameters, the reference level of the verification tool should be set to an appropriate level.
It is not intended as a precise representation of any particular system environment or a depiction of the actual
load presented by a production tester. System designers should use IBIS or other simulation tools to correlate
the timing reference load to a system environment. Manufacturers correlate to their production test conditions,
generally one or more coaxial transmission lines terminated at the tester electronics.
DUT
CK, CK#
DQ,
DQS,
DQS#
VDDQ
50ohm
Timing Reference Point
VTT = VDDQ
Timing Reference Point
Figure 183. Reference Load for AC Timing and Output Slew Rate
AS4C256M16D4
Confidential
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Rev.1.0 Aug.2019