Datasheet

From Output
Under Test
LOAD CIRCUIT
235 Ω
165 Ω
390 pF
5 V
SN74VMEH22501A
SCES3620A –DECEMBER 2004–REVISED FEBRUARY 2010 www.ti.com
Skew Characteristics for UBT
for specific worst-case V
CC
and temperature within the recommended ranges of supply voltage and operating free-air
temperature (see Figure 3)
FROM TO
PARAMETER MIN TYP
(1)
MAX UNIT
(INPUT) (OUTPUT)
t
sk(LH)
2
3A 3B ns
t
sk(HL)
2.3
t
sk(LH)
2.1
CLKAB 3B ns
t
sk(HL)
2.4
3A 3B 1
t
sk(t)
(2)
ns
CLKAB 3B 1
3A 3B 0.2 2.5
t
sk(pp)
ns
CLKAB 3B 0.2 2.9
(1) All typical values are at V
CC
= 3.3 V, T
A
= 25°C. All values are derived from TI-SPICE models.
(2) t
sk(t)
– Output-to-output skew is defined as the absolute value of the difference between the actual propagation delay for all outputs of
the same packaged device. The specifications are given for specific worst-case V
CC
and temperature and apply to any outputs switching
in opposite directions, both low to high (LH) and high to low (HL) [t
sk(t)
].
By simulating the performance of the device using the VME64x backplane (see Figure 3), the maximum peak
current in or out of the B-port output, as the devices switch from one logic state to another, was found to be
equivalent to driving the lumped load shown in Figure 4.
Figure 4. Equivalent AC Peak Output-Current Lumped Load
In general, the rise- and fall-time distribution is shown in Figure 5. Since VME devices were designed for use into
distributed loads like the VME64x backplane (B/P), there are significant differences between low-to-high (LH) and
high-to-low (HL) values in the lumped load shown in the PMI (see Figure 1 and Figure 2).
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