AD7908BRUZ Analog Devices Inc, AD7908BRUZ Datasheet - Page 27

• Manufacturer Part Number: AD7908BRUZ
• Description: IC ADC 8BIT 8CH 1MSPS 20-TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD7908BRUZ

• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Bits: 8
• Sampling Rate (per Second): 1M
• Number Of Converters: 1
• Power Dissipation (max): 13.5mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP (0.173", 4.40mm Width)
• Resolution (bits): 8bit
• Sampling Rate: 1MSPS
• Input Channel Type: Single Ended
• Supply Voltage Range - Analog: 2.7V To 5.25V
• Supply Current: 2.7mA
• Digital Ic Case Style: TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD79X8CBZ - BOARD EVALUATION FOR AD79X8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

APPLICATION HINTS
Grounding and Layout
The AD7908/AD7918/AD7928 have very good immunity to
noise on the power supplies, as can be seen by the PSRR vs.
Supply Ripple Frequency plot, Figure 6. However, care should
still be taken with regard to grounding and layout.
The printed circuit board that houses the AD7908/AD7918/
AD7928 should be designed so that the analog and digital
sections are separated and confined to certain areas of the
board. This facilitates the use of ground planes that can be
separated easily. A minimum etch technique is generally best
for ground planes as it gives the best shielding.
All four AGND pins of the AD7908/AD7918/AD7928 should
be sunk in the AGND plane. If the AD7908/AD7918/AD7928
is in a system where multiple devices require an AGND to
DGND connection, the connection should be made at only one
point in the plane. Using a star ground point, the connection
should be established as close as possible to the AD7908/
AD7918/AD7928.
Avoid running digital lines under the device, as these couple
noise onto the die. The analog ground plane should be allowed
to run under the AD7908/AD7918/AD7928 to avoid noise
coupling. The power supply lines to the AD7908/AD7918/
AD7928 should use as large a trace as possible to provide low
impedance paths and reduce the effects of glitches on the power
1
ADDITIONAL PINS REMOVED FOR CLARITY.
AD7908/
AD7918/
AD7928
V
DRIVE
DOUT
SCLK
1
DIN
CS
Figure 32. Interfacing to the DSP563xx
SRD
STD
SC2
SCK
V
DSP563xx
DD
1
Rev. B | Page 27 of 28
supply line. Fast switching signals, like clocks, should be
shielded with digital ground to avoid radiating noise to other
sections of the board, and clock signals should never be run
near the analog inputs. Avoid crossover of digital and analog
signals. Traces on opposite sides of the board should run at
right angles to each other. This reduces the effects of
feedthrough through the board. A microstrip technique is by far
the best, but is not always possible with a double sided board. In
this technique, the component side of the board is dedicated to
ground planes while signals are placed on the solder side.
Good decoupling is also important. All analog supplies should
be decoupled with 10 μF tantalum in parallel with 0.1 μF
capacitors to AGND. To achieve the best performance from
these decoupling components, they must be placed as close as
possible to the device, ideally right up against the device. The
0.1 μF capacitors should have low effective series resistance
(ESR) and effective series inductance (ESI), such as the
common ceramic types or surface mount types, which provide a
low impedance path to ground at high frequencies to handle
transient currents due to internal logic switching.
Evaluating the AD7908/AD7918/AD7928 Performance
The recommended layout for the AD7908/AD7918/AD7928 is
outlined in the AD7908/AD7918/AD7928 evaluation board.
The evaluation board package includes a fully assembled and
tested evaluation board, documentation, and software for
controlling the board from the PC via the eval-board controller.
The eval-board controller can be used in conjunction with the
AD7908/AD7918/AD7928 evaluation board, as well as many
other Analog Devices evaluation boards ending in the CB
designator, to demonstrate/evaluate the ac and dc performance
of the AD7908/AD7918/AD7928.
The software allows the user to perform ac (fast Fourier
transform) and dc (histogram of codes) tests on the
AD7908/AD7918/AD7928. The software and documentation
are on a CD shipped with the evaluation board.
AD7908/AD7918/AD7928