AD7710ARZ Analog Devices Inc, AD7710ARZ Datasheet - Page 19

• Manufacturer Part Number: AD7710ARZ
• Description: IC ADC 24BIT DIFF INP 24-SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD7710ARZ

• Data Interface: Serial
• Number Of Bits: 24
• Sampling Rate (per Second): 1.03k
• Number Of Converters: 1
• Power Dissipation (max): 45mW
• Voltage Supply Source: Analog and Digital, Dual ±
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (0.300", 7.50mm Width)
• Resolution (bits): 24bit
• Input Channel Type: Differential
• Supply Voltage Range - Digital: 4.75V To 5.25V
• Supply Current: 4.5mA
• Digital Ic Case Style: SOIC
• No. Of Pins: 24
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

REV. G
Span and Offset Limits
Whenever a system calibration mode is used, there are limits on
the amount of offset and span that can be accommodated. The
range of input span in both the unipolar and bipolar modes has
a minimum value of 0.8
2.1
The amount of offset that can be accommodated depends on
whether the unipolar or bipolar mode is being used. This offset
range is limited by the requirement that the positive full-scale
calibration limit is
range plus the span range cannot exceed 1.05 V
the span is at its minimum (0.8 V
the offset can be is (0.25
In bipolar mode, the system offset calibration range is again
restricted by the span range. The span range of the converter in
bipolar mode is equidistant around the voltage used for the
zero-scale point, thus the offset range plus half the span range
cannot exceed (1.05 V
GAIN, the offset span cannot move more than (0.05
GAIN) before the endpoints of the transfer function exceed the
input overrange limits (1.05 V
is set to the minimum (0.4
allowable offset range is (0.65
POWER-UP AND CALIBRATION
On power-up, the AD7710 performs an internal reset, which
sets the contents of the control register to a known state. How-
ever, to ensure correct calibration for the device, a calibration
routine should be performed after power-up.
The power dissipation and temperature drift of the AD7710
are low and no warm-up time is required before the initial
calibration is performed. However, if an external reference is
being used, this reference must have stabilized before calibration
is initiated.
Drift Considerations
The AD7710 uses chopper stabilization techniques to minimize
input offset drift. Charge injection in the analog switches and dc
leakage currents at the sampling node are the primary sources of
offset voltage drift in the converter. The dc input leakage current is
essentially independent of the selected gain. Gain drift within the
converter depends primarily upon the temperature tracking of the
internal capacitors. It is not affected by leakage currents.
Measurement errors due to offset drift or gain drift can be elimi-
nated at any time by recalibrating the converter or by operating
the part in the background calibration mode. Using the system
calibration mode can also minimize offset and gain errors in the
signal conditioning circuitry. Integral and differential linearity
errors are not significantly affected by temperature changes.
POWER SUPPLIES AND GROUNDING
Because the analog inputs and reference input are differential,
most of the voltages in the analog modulator are common-mode
voltages. V
currents flowing in the analog modulator. As a result, the V
input should be driven from a low impedance to minimize errors
due to charging/discharging impedances on this line. When the
internal reference is used as the reference source for the part,
AGND is the ground return for this reference voltage.
V
REF
/GAIN.
BIAS
provides the return path for most of the analog
1.05
REF
V
V
/GAIN). If the span is set to
V
REF
REF
REF
/GAIN and a maximum value of
/GAIN).
V
/GAIN. Therefore, the offset
REF
REF
V
REF
/GAIN). If the span range
/GAIN), the maximum
REF
/GAIN), the maximum
/GAIN).
REF
/GAIN. If
V
V
REF
BIAS
REF
/
/
–19–
The analog and digital supplies to the AD7710 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 multiples of the modulator sampling frequency.
The digital supply (DV
supply (AV
rate analog and digital supplies are used, the recommended
decoupling scheme is shown in Figure 9. In systems where
AV
and DV
each supply should be decoupled separately as shown in Fig-
ure 9. It is preferable that the common supply is the system’s
analog 5 V supply.
It is also important that power is applied to the AD7710 before
signals at REF IN, AIN, or the logic input pins in order to avoid
excessive current. If separate supplies are used for the AD7710
and the system digital circuitry, then the AD7710 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.
DIGITAL INTERFACE
The AD7710’s serial communications port provides a flexible
arrangement to allow easy interfacing to industry-standard
microprocessors, microcontrollers, and digital signal processors.
A serial read to the AD7710 can access data from the output
register, the control register, or from the calibration registers. A
serial write to the AD7710 can write data to the control register
or the calibration registers.
Two different modes of operation are available, optimized for
different types of interfaces where the AD7710 can act either as
master in the system (it provides the serial clock) or as slave (an
external serial clock can be provided to the AD7710). These
two modes, labeled self-clocking mode and external clocking
mode, are discussed in detail in the following sections.
Self-Clocking Mode
The AD7710 is configured for its self-clocking mode by tying
the MODE pin high. In this mode, the AD7710 provides the
serial clock signal used for the transfer of data to and from the
AD7710. This self-clocking mode can be used with processors
that allow an external device to clock their serial port including
most digital signal processors and microcontrollers such as the
68HC11 and 68HC05. It also allows easy interfacing to serial-
parallel conversion circuits in systems with parallel data commu-
nication, allowing interfacing to 74XX299 universal shift
registers without any additional decoding. In the case of shift
registers, the serial clock line should have a pull-down resistor
instead of the pull-up resistor shown in Figure 10 and Figure 11.
Figure 9. Recommended Decoupling Scheme
ANALOG
SUPPLY
DD
10 F
= 5 V and DV
DD
DD
are driven from the same 5 V supply, although
) by more than 0.3 V in normal operation. If sepa-
0.1 F
DD
DD
= 5 V, it is recommended that AV
) must not exceed the analog positive
AV
DD
AD7710
DV
DD
0.1 F
AD7710
DIGITAL +5V
SUPPLY
DD