AD7366BRUZ データシートの表示（PDF） - Analog Devices
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AD7366BRUZ Datasheet PDF : 17 Pages
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Preliminary Technical Data
terms are usually at a frequency close to the input frequencies.
As a result, the second and third order terms are specified
separately. The calculation of the intermodulation distortion is
as per the THD specification, where it is the ratio of the rms
sum of the individual distortion products to the rms amplitude
of the sum of the fundamentals expressed in dBs.
PSRR (Power Supply Rejection)
Variations in power supply affect the full-scale transition but
not the converter’s linearity. Power supply rejection is the
maximum change in the full-scale transition point due to a
change in power supply voltage from the nominal value (see
figure x).
THEORY OF OPERATION
Circuit Information
The AD7366 is a fast, dual, 2-Channel, 12-bit, Bipolar Input,
Serial A/D converter. The AD7366 can accept bipolar input
ranges of ±10V and ±5V. It can also accept a 0 to 10V unipolar
input range. The AD7366 requires VDD and VSS dual supplies for
the high voltage analog input structure. These supplies must be
equal to or greater than 11.5V. See Table 6 for the minimum
requirements on these supplies for each Analog Input Range.
The AD7366 requires a low voltage 4.75V to 5.25 V VCC supply
to power the ADC core.
Table 6. Reference and Supply Requirements for each Analog
Input Range
Selected Reference Full
AVCC
Analog Voltage Scale
(V)
Input
(V)
Input
Range (V)
Range(V)
Minimum
VDD/VSS (V)
2.5
±10
5
±11.5
±10
3.0
±12
5
±12
2.5
±5
3.0
0 to 10 2.5
3.0
±5
5
±6
5
0 to 10 5
0 to 12 5
±11.5
±11.5
±11.5
±12
The AD7366 contains two on-chip differential track-and-hold
amplifiers, two successive approximation A/D converters, and a
serial interface with two separate data output pins. It is housed
in a 24-lead TSSOP package, offering the user considerable
space-saving advantages over alternative solutions. The AD7366
requires a CONVST signal to start conversion. On the falling
edge of CONVST both track-and-holds will be placed into hold
mode and the conversions are initiated. The BUSY signal will go
high to indicate the conversions are taking place. The clock
source for each successive approximation ADC is provided by
an internal oscillator. The BUSY signal will go low to indicate
the end of conversion. On the falling edge of BUSY the track-
AD7366
and-hold will return to track mode. Once the conversion is
finished, the serial clock input accesses data from the part.
The AD7366 has an on-chip 2.5 V reference that can be
overdriven when an external reference is preferred. If the
internal reference is to be used elsewhere in a system, then the
output from DCAPA & DCAPB must first be buffered. On Power
up the REFSEL pin must be tied to either a high or low logic
state to select either the internal or external reference option. If
the internal reference is the preferred option, the user must tie
the REFSEL pin logic high. Alternatively, if REFSEL is tied to
GND then an external reference can be supplied to both ADC’s
through DCAPA & DCAPB pins.
The analog inputs are configured as two single ended inputs
for each ADC. The various different input voltage ranges
can be selected by programming the RANGE bits as shown in
Table 7.
Converter Operation
The AD7366 has two successive approximation analog-to-
digital converters, each based around two capacitive DACs.
Figure 3 and Figure 4 show simplified schematics of one of
these ADCs in acquisition and conversion phase, respectively.
The ADC is comprised of control logic, a SAR, and two
capacitive DACs. In Figure 3 (the acquisition phase), SW2 is
closed and SW1 is in Position A, the comparator is held in a
balanced condition, and the sampling capacitor arrays acquire
the signal on the input.
VIN
AGND
A
SW1 B
CAPACITIVE
DAC
SW2
CONTROL
LOGIC
COMPARATOR
Figure 3 ADC Acquisition Phase
When the ADC starts a conversion (Figure 4), SW2 opens and
SW1 moves to Position B, causing the comparator to become
unbalanced. The control logic and the charge redistribution
DACs are used to add and subtract fixed amounts of charge
from the sampling capacitor to bring the comparator back into
a balanced condition. When the comparator is rebalanced, the
conversion is complete. The control logic generates the ADC
output code.
Rev. PrG | Page 11 of 17
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