TransmissionLine
4.0pF
1.85pF
Z0=50
(seenote)
Tester PinElectronics
Data SheetTimingReferencePoint
Output
Under
Test
42
3.5nH
DevicePin
(seenote)
Vref
Vref =VIL MAX(orVOL MAX)
Vref =VIH MIN(orVOH MIN)
SPRS457E
– MARCH 2009 – REVISED JUNE 2011
6
Peripheral Information and Electrical Specifications
6.1
Parameter Information Device-Specific Information
A.
The data sheet provides timing at the device pin. For output timing analysis, the tester pin electronics and its
transmission line effects must be taken into account. A model of the tester pin electronics is shown in
Figure 6-1. A
transmission line with a delay of 2 ns or longer can be used to produce the desired transmission line effect. The
transmission line is intended as a load only. It is not necessary to add or subtract the transmission line delay (2 ns or
longer) from the data sheet timings.
Input requirements in this data sheet are tested with an input slew rate of
< 4 Volts per nanosecond (4 V/ns) at the
device pin and the input signals are driven between 0V and the appropriate I/O supply for the signal.
Figure 6-1. Test Load Circuit for AC Timing Measurements
The load capacitance value stated is only for characterization and measurement of AC timing signals. This
load capacitance value does not indicate the maximum load the device is capable of driving.
6.1.1
Signal Transition Levels
All input and output timing parameters are referenced to Vref for both "0" and "1" logic levels. For 3.3 V I/O,
Vref = 1.65 V. For 1.8 V I/O, Vref = 0.9 V.
Figure 6-2. Input and Output Voltage Reference Levels for AC Timing Measurements
All rise and fall transition timing parameters are referenced to VIL MAX and VIH MIN for input clocks,
VOLMAX and VOH MIN for output clocks.
Figure 6-3. Rise and Fall Transition Time Voltage Reference Levels
6.1.2
Timing Parameters and Board Routing Analysis
The timing parameter values specified in this data sheet do not include delays by board routings. As a
good board design practice, such delays must always be taken into account. Timing values may be
adjusted by increasing/decreasing such delays. TI recommends utilizing the available I/O buffer
information specification (IBIS) models to analyze the timing characteristics correctly. To properly use IBIS
models to attain accurate timing analysis for a given system, see the Using IBIS Models for Timing
Analysis Application Report (literature number
SPRA839). If needed, external logic hardware such as
buffers may be used to compensate any timing differences.
76
Peripheral Information and Electrical Specifications
Copyright
2009–2011, Texas Instruments Incorporated