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5
RESISTOR =
1 MEGAOHM
POWER SUPPLIES
CMOS devices have low power requirements and the abil-
ity to operate over a wide range of supply voltages. These
two characteristics allow CMOS designs to be implemented
using inexpensive, conventional power supplies, instead of
switching power supplies and power supplies with cooling
fans. In addition, batteries may be used as either a primary
power source or for emergency backup.
The absolute maximum power supply voltage for 14000
Series Metal–gate CMOS is 18.0 Vdc. Figure 4 offers some
insight as to how this specification was derived. In the figure,
V S is the maximum power supply voltage and I S is the sus-
taining current of the latch–up mode. The value of V S was
chosen so that the secondary breakdown effect may be
avoided.
In an ideal system design, a power supply should be
designed to deliver only enough current to insure proper
operation of all devices. The obvious benefit of this type
design is cost savings; an added benefit is protection against
CHAPTER 5
5–4
4
1
2
3
Figure 2. Typical Manufacturing Work Station
I DD
LATCH
UP MODE
I S
V S
V S = DATA SHEET MAXIMUM SUPPLY RATING
Figure 3. Secondary Breakdown Characteristics
NOTES: 1. 1/16 inch conductive sheet stock covering bench
top work area.
2. Ground strap.
3. Wrist strap in contact with skin.
4. Static neutralizer. (Ionized air blower directed at
work.) Primarily for use in areas where direct
grounding is impractical.
5. Room humidifier. Primarily for use in areas where
the relative humidity is less than 45%. Caution:
building heating and cooling systems usually dry
the air causing the relative humidity inside of
buildings to be less than outside humidity.
the possibility of latch–up related failures. This system
protection can be provided by the power supply filter and/or
voltage regulator.
CMOS devices can be used with battery or battery backup
systems. A few precautions should be taken when designing
battery–operated systems:
1. The recommended power supply voltage should be ob-
served. For battery backup systems such as the one in
Figure 5, the battery voltage must be at least 3.7 Volts
(3 Volts from the minimum power supply voltage and
0.7 Volts to account for the voltage drop across the se-
ries diode).
2. Inputs that might go above the battery backup voltage
should either use a series resistor to limit the input cur-
rent to less than 10 mA or use the MC14049UB or
MC14050B high–to–low voltage translators.
3. Outputs that are subject to voltage levels above V DD or
below V SS should be protected with a series resistor to
limit the current to less than 10 mA or with clamping
diodes.
SECONDARY
BREAKDOWN
LOW CURRENT
JUNCTION
AVALANCHE
V DD
MOTOROLA CMOS LOGIC DATA
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