AD977AARZ Analog Devices Inc, AD977AARZ Datasheet - Page 23

• Manufacturer Part Number: AD977AARZ
• Description: 200 KSPS 16 BIT ADC
• Manufacturer: Analog Devices Inc

Specifications of AD977AARZ

• Number Of Bits: 16
• Sampling Rate (per Second): 200k
• Data Interface: Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 100mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (0.300", 7.50mm Width)
• Number Of Elements: 1
• Resolution: 16Bit
• Architecture: SAR
• Sample Rate: 200KSPS
• Input Polarity: Unipolar/Bipolar
• Input Type: Voltage
• Differential Input: No
• Power Supply Requirement: Analog and Digital
• Single Supply Voltage (typ): 5V
• Single Supply Voltage (min): 4.75V
• Single Supply Voltage (max): 5.25V
• Dual Supply Voltage (typ): Not RequiredV
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Power Dissipation: 100mW
• Differential Linearity Error: ±3LSB
• Integral Nonlinearity Error: ±3LSB
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 20
• Package Type: SOIC W
• Input Signal Type: Single-Ended
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The ADSP-2181 SPORT0 will now remain synchronized to the
external discontinuous clock for all subsequent conversions.
POWER SUPPLIES AND DECOUPLING
The AD977/AD977A has two power supply input pins. V
and V
portions, respectively. V
analog circuitry, and V
digital circuitry. The AD977/AD977A is designed to be inde-
pendent of power supply sequencing and thus free from supply
voltage induced latchup.
With high performance linear circuits, changes in the power
supplies can result in undesired circuit performance. Optimally,
well regulated power supplies should be chosen with less than
1% ripple. The ac output impedance of a power supply is a
complex function of frequency and will generally increase with
frequency. Thus, high frequency switching, such as that encoun-
tered with digital circuitry, requires the fast transient currents
that most power supplies cannot adequately provide. Such a
situation results in large voltage spikes on the supplies. To com-
pensate for the finite ac output impedance of most supplies,
charge “reserves” should be stored in bypass capacitors. This
will effectively lower the supplies impedance presented to the
AD977/AD977A V
of these spikes. Decoupling capacitors, typically 0.1 µF, should
be placed close to the power supply pins of the AD977/AD977A
to minimize any inductance between the capacitors and the
V
The AD977/AD977A may be operated from a single 5 V
supply. When separate supplies are used, however, it is benefi-
cial to have larger capacitors, 10 µF, placed between the logic
supply (V
analog supply (V
Additionally, 10 µF capacitors should be located in the vicinity
of the ADC to further reduce low frequency ripple. In systems
where the device will be subjected to harsh environmental noise,
additional decoupling may be required.
GROUNDING
The AD977/AD977A has three ground pins; AGND1, AGND2
and DGND. The analog ground pins are the “high quality”
ground reference points and should be connected to the system
analog common. AGND2 is the ground to which most internal
ADC analog signals are referenced. This ground is most sus-
ceptible to current induced voltage drops and thus must be
ANA
and V
DIG
DIG
provide the supply voltages to the analog and digital
SPORT0 CNTRL REG = 0x300F
ADSP-2181
DIG
) and digital common (DGND) and between the
pins.
SCLK0
RFS0
ANA
DR0
PF1
PF0
ANA
) and the analog common (AGND2).
DIG
and V
ANA
OSCILLATOR
is the 5 V supply for the on-chip
is the 5 V supply for the on-chip
DIG
pins and reduce the magnitude
DATACLK
R/C
DATA
CS
EXT/INT
TAG
AD977A
AD977/
ANA
connected with the least resistance back to the power supply.
AGND1 is the low current analog supply ground and should be
the analog common for the external reference, input op amp
drive circuitry and the input resistor divider circuit. By applying
the inputs referenced to this ground, any ground variations will
be offset and have a minimal effect on the resulting analog input
to the ADC. The digital ground pin, DGND, is the reference
point for all of the digital signals that control the AD977/AD977A.
The AD977/AD977A can be powered with two separate power
supplies or with a single analog supply. When the system digital
supply is noisy, or fast switching digital signals are present, it is
recommended to connect the analog supply to both the V
and V
the remaining digital circuitry. With this configuration, AGND1,
AGND2 and DGND should be connected back at the ADC.
When there is significant bus activity on the digital output pins,
the digital and analog supply pins on the ADC should be
separated. This would eliminate any high speed digital noise
from coupling back to the analog portion of the AD977/
AD977A. In this configuration, the digital ground pin DGND
should be connected to the system digital ground and be
separate from the AGND pins.
BOARD LAYOUT
Designing with high resolution data converters requires careful
attention to board layout. Trace impedance is a significant issue.
A 1.22 mA current through a 0.5 Ω trace will develop a voltage
drop of 0.6 mV, which is 2 LSBs at the 16-bit level over the
20 volt full-scale range. Ground circuit impedances should be
reduced as much as possible since any ground potential differ-
ences between the signal source and the ADC appear as an error
voltage in series with the input signal. In addition to ground
drops, inductive and capacitive coupling needs to be considered.
This is especially true when high accuracy analog input signals
share the same board with digital signals. Thus, to minimize input
noise coupling, the input signal leads to V
return leads from AGND should be kept as short as possible.
In addition, power supplies should also be decoupled to filter
out ac noise.
Analog and digital signals should not share a common path.
Each signal should have an appropriate analog or digital return
routed close to it. Using this approach, signal loops enclose a
small area, minimizing the inductive coupling of noise. Wide PC
tracks, large gauge wire and ground planes are highly recom-
mended to provide low impedance signal paths. Separate analog
and digital ground planes are also recommended with a single
interconnection point to minimize ground loops. Analog signals
should be routed as far as possible from high speed digital sig-
nals and should only cross them, if absolutely necessary, at right
angles.
In addition, it is recommended that multilayer PC boards be used
with separate power and ground planes. When designing the
separate sections, careful attention should be paid to the layout.
DIG
pins of the AD977/AD977A and the system supply to
AD977/AD977A
IN
and the signal
ANA