ADC10061 National Semiconductor Corporation, ADC10061 Datasheet - Page 11

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ADC10061

Manufacturer Part Number
ADC10061
Description
ADC10061 - 10-Bit 600 NS A/D Converter With Input Multiplexer And Sample/Hold, Package: Soic Wide, Pin Nb=20
Manufacturer
National Semiconductor Corporation
Datasheet

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Applications Information
4.0 INHERENT SAMPLE-AND-HOLD
Because the ADC10061, ADC10062, and ADC10064
sample the input signal once during each conversion, they
are capable of measuring relatively fast input signals without
the help of an external sample-hold. In a non-sampling
successive-approximation A/D converter, regardless of
speed, the input signal must be stable to better than
LSB during each conversion cycle or significant errors will
result. Consequently, even for many relatively slow input
signals, the signals must be externally sampled and held
constant during each conversion if a SAR with no internal
sample-and-hold is used.
Because they incorporate a direct sample/hold control input,
the ADC10061, ADC10062, and ADC10064 are suitable for
use in DSP-based systems. The S/H input allows synchro-
nization of the A/D converter to the DSP system’s sampling
rate
ADC10064s.
The ADC10061, ADC10062, and ADC10064 can perform
accurate conversions of input signals with frequency compo-
nents from DC to over 160 kHz.
5.0 POWER SUPPLY CONSIDERATIONS
The ADC10061, ADC10062, and ADC10064 are designed to
operate from a +5V (nominal) power supply. There are two
supply pins, AV
external bypass capacitors for the analog and digital portions
of the circuit. To guarantee accurate conversions, the two
supply pins should be connected to the same voltage
source, and each should be bypassed with a 0.1 µF ceramic
capacitor in parallel with a 10 µF tantalum capacitor. De-
pending on the circuit board layout and other system con-
siderations, more bypassing may be necessary.
FIGURE 4. Typical Connection. Note the multiple bypass capacitors on the reference and power supply pins. If V
Considerations”). AGND and DGND should be at the same potential. V
is not grounded, it should also be bypassed to analog ground using multiple capacitors (see 5.0 “Power Supply
Pin 17 is normally left open, but optional “speedup” resistor R
and
to
CC
other
and DV
ADC10061s,
CC
. These pins allow separate
ADC10062s,
(Continued)
±
and
1/2
11
The ADC10061 has a single ground pin, and the ADC10062
and ADC10064 each have separate analog and digital
ground pins for separate bypassing of the analog and digital
supplies. The devices with separate analog and digital
ground pins should have their ground pins connected to the
same potential, and all grounds should be “clean” and free of
noise.
In systems with multiple power supplies, careful attention to
power supply sequencing may be necessary to avoid over-
driving inputs. The A/D converter’s power supply pins should
be at the proper voltage before digital or analog signals are
applied to any of the other pins.
6.0 LAYOUT AND GROUNDING
In order to ensure fast, accurate conversions from the
ADC10061, ADC10062, and ADC10064, it is necessary to
use appropriate circuit board layout techniques. The analog
ground return path should be low-impedance and free of
noise from other parts of the system. Noise from digital
circuitry can be especially troublesome, so digital grounds
should always be separate from analog grounds. For best
performance, separate ground planes should be provided for
the digital and analog parts of the system.
All bypass capacitors should be located as close to the
converter as possible and should connect to the converter
and to ground with short traces. The analog input should be
isolated from noisy signal traces to avoid having spurious
signals couple to the input. Any external component (e.g., a
filter capacitor) connected across the converter’s input
should be connected to a very clean ground return point.
Grounding the component at the wrong point will result in
reduced conversion accuracy.
SA
can be used to reduce the conversion time.
IN0
is shown with an input protection network.
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01102015
REF−

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