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23
DC CHARACTERISTICS for ‘ACT Family Devices (continued)
Symbol
Conditions
Unit
74ACT
VCC
(V)
Parameter
Symbol
Conditions
Unit
TA =
–40
°C to +85°C
TA = 25°C
VCC
(V)
Parameter
Symbol
Conditions
Unit
Guaranteed Limits
Typ
VCC
(V)
Parameter
4.5
0.36
0.44
V
IOL
24 mA
5.5
0.36
0.44
IOL
24 mA
IIN
Maximum Input
55
±01
±10
A
VI =VCC GND
Leakage Current
5.5
±0.1
±1.0
A
VI = VCC, GND
ICCT
Additional Max. ICC/Input
5.5
0.6
1.5
mA
VI = VCC – 2.1V
IOLD
Minimum Dynamic
Ot
t C
t
5.5
75
mA
VOLD = 1.65 V Max
IOHD
Output Current
5.5
–75
mA
VOHD = 3.85 V Min
ICC
Maximum Quiescent
55
80
A
VIN =VCC or GND
Q
Supply Current
5.5
8.0
80
A
VIN = VCC or GND
* All outputs loaded; thresholds on input associated with output under test.
Maximum test duration 2.0 ms, one output loaded at a time.
TEST LOAD
50 pF
tr = 3 ns
tf = 3 ns
OPEN
2 × VCC
500
450
50 SCOPE
DUT
Figure 1–21. AC Tri-State Loading Circuit
tPZH
tPHZ
tPZL
tPLZ
AC Loading and Waveforms
Loading Circuit
Figure 1–21 shows the AC loading circuit used in
characterizing and specifying propagation delays of all
FACT devices (‘AC and ‘ACT) unless otherwise specified
in the data sheet of a specific device.
The use of this load, differs somewhat from previous
(HCMOS) practice, provides more meaningful information
and minimizes problems of instrumentation and customer
correlation. In the past, +25
°C propagation delays for TTL
devices were specified with a load of 15 pF to ground; this
required great care in building test jigs to minimize stray
capacitance and implied the use of high impedance, high
frequency scope probes. FAST circuits changed to 50 pF of
capacitance allowing more leeway in stray capacitance and
also loading the device during rising or falling output
transitions. This more closely resembles the inloading to be
expected in average applications and thus gives the designer
more useful delay figures. We have incorporated this
scheme into the FACT product line. The net effect of the
change in AC load is to increase the average observed
propagation delay by about 1 ns.
The 500 ohm resistor to ground can be a high frequency
passive probe for a sampling oscilloscope, which costs much
less than the equivalent high impedance probe. Alternately,
the 500 ohm resistor to ground can simply be a 450 ohm
resistor feeding into a 50 ohm coaxial cable leading to a
sampling scope input connector, with the internal 50 ohm
termination of the scope completing the path to ground. This
is the preferred scheme for correlation. (See Figure 1–21.)
With this scheme there should be a matching cable from the
device input pin to the other input of the sampling scope; this
also serves as a 50 ohm termination for the pulse generator
that supplies the input signal.
Shown in Figure 1–21 is a second 500 ohm resistor from
the device output to a switch. For most measurements this
switch is open; it is closed for measuring one set of the
Enable/Disable
parameters
(LOW-to-OFF
and
OFF-to-LOW) of a 3-state output. With the switch closed,
the pair of 500 ohm resistors and the 2
× VCC supply voltage
establish a quiescent HIGH level.