ADC0809CCN/NOPB National Semiconductor, ADC0809CCN/NOPB Datasheet - Page 10

• Manufacturer Part Number: ADC0809CCN/NOPB
• Description: IC ADC 8BIT MPU 8CH MUX 28-DIP
• Manufacturer: National Semiconductor

Specifications of ADC0809CCN/NOPB

• Number Of Bits: 8
• Number Of Converters: 1
• Power Dissipation (max): 875mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 28-DIP (0.600", 15.24mm)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *ADC0809CCN; *ADC0809CCN/NOPB; ADC0809; ADC0809CCN

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age must also be near the center of the supply because the
analog switch tree changes from N-channel switches to P-
channel switches. These limitations are automatically satis-
fied in ratiometric systems and can be easily met in ground
referenced systems.
The ADC0808 needs less than a milliamp of supply current
so developing the supply from the reference is readily ac-
complished. In Figure 11 a ground referenced system is
shown which generates the supply from the reference. The
buffer shown can be an op amp of sufficient drive to supply
the milliamp of supply current and the desired bus drive, or if
a capacitive bus is driven by the outputs a large capacitor will
supply the transient supply current as seen in Figure 12. The
LM301 is overcompensated to insure stability when loaded by
the 10 μF output capacitor.
Conversion System Using Trimmed Supply
FIGURE 9. Ratiometric Conversion System
FIGURE 10. Ground Referenced
10
Figure 10 shows a ground referenced system with a separate
supply and reference. In this system, the supply must be
trimmed to match the reference voltage. For instance, if a
5.12V is used, the supply should be adjusted to the same
voltage within 0.1V.
The top and bottom ladder voltages cannot exceed V
ground, respectively, but they can be symmetrically less than
V
should always be near the center of the supply. The sensitivity
of the converter can be increased, (i.e., size of the LSB steps
decreased) by using a symmetrical reference system. In Fig-
ure 13, a 2.5V reference is symmetrically centered about
V
system with a 2.5V reference allows the LSB bit to be half the
size of a 5V reference system.
CC
CC
/2 since the same current flows in identical resistors. This
and greater than ground. The center of the ladder voltage
567224
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CC
and