AD7715ANZ-3 Analog Devices Inc, AD7715ANZ-3 Datasheet - Page 21

• Manufacturer Part Number: AD7715ANZ-3
• Description: IC ADC 16BIT SIGMA-DELTA 16DIP
• Manufacturer: Analog Devices Inc

Specifications of AD7715ANZ-3

• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Bits: 16
• Sampling Rate (per Second): 500
• Number Of Converters: 1
• Power Dissipation (max): 9.5mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 16-DIP (0.300", 7.62mm)
• Resolution (bits): 16bit
• Input Channel Type: Differential
• Supply Voltage Range - Analogue: 3V To 3.6V
• Supply Voltage Range - Digital: 3V To 5.25V
• Supply Current: 600µA
• No. Of: RoHS Compliant
• Sampling Rate: 19.2kSPS
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7715-3EBZ - BOARD EVALUATION FOR AD7715
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

REV. C
Measurement errors due to offset drift or gain drift can be elimi-
nated at any time by recalibrating the converter. Using the sys-
tem calibration mode can also minimize offset and gain errors in
the signal conditioning circuitry. Integral and differential linear-
ity errors are not significantly affected by temperature changes.
POWER SUPPLIES
There is no specific power sequence required for the AD7715;
either the AV
the latch-up performance of the AD7715 is good, it is important
that power is applied to the AD7715 before signals at REF IN,
AIN or the logic input pins in order to avoid excessive currents.
If this is not possible, then the current which flows in any of
these pins should be limited. If separate supplies are used for
the AD7715 and the system digital circuitry, then the AD7715
should be powered up first. If it is not possible to guarantee
this, then current limiting resistors should be placed in series
with the logic inputs to again limit the current.
During normal operation the AD7715 analog supply (AV
should always be greater than or equal to its digital supply (DV
Supply Current
The current consumption on the AD7715 is specified for sup-
plies in the range +3 V to +3.6 V and in the range +4.75 V to
+5.25 V. The part operates over a +2.85 V to +5.25 V supply
range and the I
over this range. Figure 5 shows the variation of the typical
I
2.4576 MHz external clock at +25 C. The AD7715 is operated
in unbuffered mode. The relationship shows that the I
minimized by operating the part with lower V
on the AD7715 is also minimized by using an external master
clock or by optimizing external components when using the on-
chip oscillator circuit.
Grounding and Layout
Since the analog inputs and reference input are differential,
most of the voltages in the analog modulator are common-mode
voltages. The excellent common-mode rejection of the part will
remove common-mode noise on these inputs. The analog and
digital supplies to the AD7715 are independent and separately
pinned out to minimize coupling between the analog and digital
sections of the device. The digital filter will provide rejection of
broadband noise on the power supplies, except at integer mul-
tiples of the modulator sampling frequency. The digital filter
DD
with V
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
1.0
0
2.85
DD
DD
voltage for both a 1 MHz external clock and a
Figure 5. I
3.15
DD
or the DV
for the part varies as the supply voltage varies
SUPPLY VOLTAGE (AV
3.45
MCLK IN = 2.4576MHz
DD
MCLK IN = 1MHz
3.75
DD
vs. Supply Voltage
supply can come up first. While
4.05
DD
& DV
4.35
DD
4.65
) – Volts
DD
voltages. I
4.95
DD
5.25
DD
is
DD
)
DD
).
–21–
also removes noise from the analog and reference inputs pro-
vided those noise sources do not saturate the analog modulator.
As a result, the AD7715 is more immune to noise interference
that a conventional high resolution converter. However, because
the resolution of the AD7715 is so high and the noise levels
from the AD7715 so low, care must be taken with regard to
grounding and layout.
The printed circuit board which houses the AD7715 should be
designed such that the analog and digital sections are separated
and confined to certain areas of the board. This facilitates the
use of ground planes which can be separated easily. A minimum
etch technique is generally best for ground planes as it gives the
best shielding. Digital and analog ground planes should only be
joined in one place. If the AD7715 is the only device requiring
an AGND to DGND connection, then the ground planes
should be connected at the AGND and DGND pins of the
AD7715. If the AD7715 is in a system where multiple devices
require AGND to DGND connections, the connection should
still be made at one point only, a star ground point which
should be established as close as possible to the AD7715.
Avoid running digital lines under the device as these will couple
noise onto the die. The analog ground plane should be allowed
to run under the AD7715 to avoid noise coupling. The power
supply lines to the AD7715 should use as large a trace as pos-
sible to provide low impedance paths and reduce the effects of
glitches on the power 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 will reduce 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 important when using high resolution
ADCs. All analog supplies should be decoupled with 10 F
tantalum in parallel with 0.1 F capacitors to AGND. To
achieve the best from these decoupling components, they must
be placed as close as possible to the device, ideally right up
against the device. All logic chips should be decoupled with
0.1 F disc ceramic capacitors to DGND. In systems where a
common supply voltage is used to drive both the AV
DV
AV
mended analog supply decoupling capacitors between the AV
pin of the AD7715 and AGND and the recommended digital
supply decoupling capacitor between the DV
AD7715 and DGND.
Evaluating the AD7715 Performance
The recommended layout for the AD7715 is outlined in the
evaluation board for the AD7715. The evaluation board pack-
age includes a fully assembled and tested evaluation board,
documentation, software for controlling the board over the
printer port of a PC and software for analyzing the AD7715’s
performance on the PC. For the AD7715-5, the evaluation
board order number is EVAL-AD7715-5EB and for the
AD7715-3, the order number is EVAL-AD7715-3EB.
Noise levels in the signals applied to the AD7715 may also
affect performance of the part. The AD7715 software evaluation
DD
DD
supply is used. This supply should have the recom-
of the AD7715, it is recommended that the system’s
DD
AD7715
pin of the
DD
and
DD