7-
16
7-3. Low Voltage
There is a new family of logic that offers lower dynamic power consumption, lower operating
voltages, higher output drive, faster AC speed, lower noise and better dynamic thresholds than
HC CMOS. These features make this family attractive for low power applications such as battery
operated portable applications (that is, laptop computers, pagers, phones, etc.).
In order to achieve this new improved level of performance, the manufacturers of this LV (low
voltage) family of logic ICs have redesigned the internal structure of the device. Some
manufacturers have changed the input structure by eliminating the input protection diode to V
CC
.
Similarly, the design of the output structure also has changed by eliminating the output protection
diode to V
CC
and replacing it with a N-Channel pull-up transistor. As a result of these changes,
the Tracker signatures of the LV logic family are different from the conventional HC logic family.
The Tracker 2700 has a "3V" test range which has been optimized for this LV logic. SMT is an
abbreviation for surface mount technology and refers to the manufacturing technology type in
which the LV logic family is commonly available.
1. Select the 3V 10 kΩ
ΩΩ
Ω Range.
2. Set the test signal frequency to 60 Hz.
3. Place or clip the black test lead from the Tracker 2700's Common terminal to the IC's ground
pin. For this example, the ground pin of the 74LVQ245 is pin 10.
4. Use the red test lead from the Tracker 2700's A test terminal and probe each pin of the IC.
For this example, pins 2 to 9 and 11 to 18 are all buffer circuits so they will have identical
signatures. (Note: This is only for ICs out of circuit.)
5. Use the red test lead from the Tracker 2700's A test terminal and probe the enable input pins.
For this example, the enable pins of the 74LVQ245 are pin 1 and 19 and will have the same
signatures. (Note: This is only for ICs out of circuit.)
6. Use the red test lead from the Tracker 2700's A test terminal and probe the power supply V
CC
input pin. For this example, the V
CC
pin of the 74LVQ245 is pin 20.
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