ADC0806 National Semiconductor, ADC0806 Datasheet - Page 15

• Manufacturer Part Number: ADC0806
• Description: 500 ns A/D Converter with S/H Function and Input Multiplexer
• Manufacturer: National Semiconductor

Applications Information
V
to minimize noise.
V
be bypassed to a clean, quiet point in the analog ground
plane with a 0.1 µF capacitor. DO NOT allow this pin to float.
2.0 THE ANALOG INPUT
The analog input of the ADC08060 is a switch followed by an
integrator. The input capacitance changes with the clock
level, appearing as 3 pF when the clock is low, and 4 pF
when the clock is high. Since a dynamic capacitance is more
RT
RM
should always be at least 1.0V more positive than V
(pin 9) is the center of the reference ladder and should
FIGURE 3. Driving the reference to force desired values requires driving with a low impedance source.
(Continued)
RB
15
difficult to drive than is a fixed capacitance, choose an
amplifier that can drive this type of load. The LMH6702 has
been found to be a good amplifier to drive the ADC08060.
Figure 4 shows an example of an input circuit using the
LMH6702. Any input amplifier should incorporate some gain
as operational amplifiers exhibit better phase margin and
transient response with gains above 2 or 3 than with unity
gain. If an overall gain of less than 3 is required, attenuate
the input and operate the amplifier at a higher gain, as
shown in Figure 4.
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