AD7699 Analog Devices, AD7699 Datasheet - Page 18

• Manufacturer Part Number: AD7699
• Description: 16-Bit, 8-Channel, 500 kSPS PulSAR ADC
• Manufacturer: Analog Devices

Specifications of AD7699

• Resolution (bits): 16bit
• # Chan: 8
• Sample Rate: 500kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Bip,SE-Uni
• Ain Range: (Vref) p-p,4 V p-p,Bip (Vref) x 0.5,Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: CSP

AD7699
DRIVER AMPLIFIER CHOICE
Although the
meet the following requirements:
•
•
•
Table 7. Recommended Driver Amplifiers
Amplifier
ADA4841-x
AD8655
AD8021
AD8022
OP184
AD8605,
The noise generated by the driver amplifier must be kept
as low as possible to preserve the SNR and transition noise
performance of the AD7699. Note that the
noise much lower than most of the other 16-bit ADCs and,
therefore, can be driven by a noisier amplifier to meet a given
system noise specification. The noise from the amplifier is
filtered by the
made by R
Because the typical noise of the
V
where:
f
(14.7 MHz in full BW or 670 kHz in ¼ BW) or the cutoff
frequency of an input filter, if one is used.
N is the noise gain of the amplifier (for example, 1 in buffer
configuration).
e
nV/√Hz.
For ac applications, the driver should have a THD perfor-
mance commensurate with the AD7699. Figure 12 shows
THD vs. frequency for the AD7699.
For multichannel, multiplexed applications on each input
or input pair, the driver amplifier and the
input circuit must settle a full-scale step onto the capacitor
array at a 16-bit level (0.0015%). In amplifier data sheets,
settling at 0.1% to 0.01% is more commonly specified. This
may differ significantly from the settling time at a 16-bit
level and should be verified prior to driver selection.
SNR
−3dB
N
REF
is the equivalent input noise voltage of the op amp, in
AD8615
is the input bandwidth in megahertz of the AD7699
= 5 V), the SNR degradation due to the amplifier is
LOSS
AD7699
=
IN
20
and C
log
AD7699
Typical Application
Very low noise, small, and low power
5 V single supply, low noise
Very low noise and high frequency
Low noise and high frequency
Low power, low noise, and low frequency
5 V single supply, low power
⎛
⎜
⎜
⎜
⎜
⎝
is easy to drive, the driver amplifier must
IN
35
or by an external filter, if one is used.
2
analog input circuit low-pass filter
+
π
2
35
f
−
3dB
AD7699
(
Ne
N
)
2
is 35 μV rms (with
AD7699
⎞
⎟
⎟
⎟
⎟
⎠
AD7699
has a
analog
Rev. A | Page 18 of 28
VOLTAGE REFERENCE OUTPUT/INPUT
The
internal voltage reference, an external reference, or an external
buffered reference.
The internal reference of the
performance and can be used in almost all applications. There
are five possible choices of voltage reference schemes briefly
described in Table 8 with more details in each of the following
sections.
Internal Reference
The internal reference can be set for a 4.096 V output as
detailed in Table 8. With the internal reference enabled, the
band gap voltage is also present on the REFIN pin, which
requires an external 0.1 μF capacitor. Because the current
output of REFIN is limited, it can be used as a source if followed
by a suitable buffer, such as the AD8605.
When using the 4.096 V internal reference, the internal
temperature sensor is disabled. Note that, when using the
temperature sensor, the output is straight binary referenced
from the
The internal reference is temperature-compensated to within
15 mV. The reference is trimmed to provide a typical drift of
3 ppm/°C.
External Reference and Internal Buffer
For improved drift performance, an external reference can be
used with the internal buffer. The external reference is connected
to REFIN, and the output is produced on the REF pin. For
applications requiring the use of the temperature sensor, an
external reference must be used with or without the internal
buffer. The internal temperature sensor measures the internal
temperature of the
system calibration. Refer to Table 8 for register details. With the
buffer enabled, the gain is unity and is limited to an input/output of
4.096 V.
The internal reference buffer is useful in multiconverter applica-
tions because a buffer is typically required in these applications. In
addition, a low power reference can be used because the internal
buffer provides the necessary performance to drive the SAR
architecture of the AD7699.
External Reference
In any of the five voltage reference schemes, an external refer-
ence can be connected directly on the REF pin because the output
impedance of REF is >5 kΩ. To reduce power consumption, the
reference and buffer can be powered down independently or
together for the lowest power consumption. When only using the
external reference (and optional reference buffer as shown in
Figure 34), an internal buffer is disabled. Refer to Table 8 for
register details. For improved drift performance, an external
reference such as the
AD7699
AD7699
allows the choice of a very low temperature drift
GND pin.
AD7699
ADR43x
and is thus useful for performing a
AD7699
or
ADR44x
provides excellent
is recommended.
Data Sheet