AD7710ANZ Analog Devices Inc, AD7710ANZ Datasheet - Page 15

• Manufacturer Part Number: AD7710ANZ
• Description: IC ADC SIGNAL CONDITIONING 24DIP
• Manufacturer: Analog Devices Inc

Specifications of AD7710ANZ

• 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: Through Hole
• Package / Case: 24-DIP (0.300", 7.62mm)
• Resolution (bits): 24bit
• Sampling Rate: 1.02kSPS
• Input Channel Type: Single Ended
• Supply Voltage Range - Digital: 4.75V To 5.25V
• Supply Current: 4.5mA
• Digital Ic Case Style: DIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

REV. G
Antialias Considerations
The digital filter does not provide any rejection at integer mul-
tiples of the modulator sample frequency (n 19.5 kHz, where
n = 1, 2, 3 . . . ). This means that there are frequency bands
where noise passes unattenuated to the output. However, due to
the AD7710’s high oversampling ratio, these bands occupy only
a small fraction of the spectrum, and most broadband noise is
filtered. In any case, because of the high oversampling ratio a
simple RC, single-pole filter is generally sufficient to attenuate
the signals in these bands on the analog input and thus provide
adequate antialiasing filtering.
If passive components are placed in front of the AD7710, ensure
that the source impedance is low enough to keep from intro-
ducing gain errors in the system. The dc input impedance for
the AD7710 is over 1 G . The input appears as a dynamic
load that varies with the clock frequency and with the selected
gain (see Figure 7). The input sample rate, as shown in Table III,
determines the time allowed for the analog input capacitor C
to be charged. External impedances result in a longer charge
time for this capacitor, which may result in gain errors being
introduced on the analog inputs. Table IV shows the allowable
external resistance/capacitance values that do not introduce gain
error to the 16-bit level, while Table V shows the allowable
external resistance/capacitance values that do not introduce gain
error to the 20-bit level. Both inputs of the differential input
channels look into similar input circuitry.
Table IV. External Series Resistance That Do Not Introduce
16-Bit Gain Error
Gain
1
2
4
8–128 17.6 k
Table V. External Series Resistance That Do Not Introduce
20-Bit Gain Error
Gain
1
2
4
8–128 13.4 k
f
3 dB
wide (f
0
184 k
88.6 k
41.4 k
0
145 k
70.5 k
31.8 k
AIN
3 dB
Figure 7. Analog Input Impedance
is cutoff frequency selected by FS0 to FS11),
SWITCHING FREQUENCY DEPENDS ON
f
CLKIN
External Capacitance (pF)
50
45.3 k
22.1 k
10.6 k
4.8 k
External Capacitance (pF)
50
34.5 k
16.9 k
8.0 k
3.6 k
AND SELECTED GAIN
7k
11.5pF TYP
R
INT
TYP
100
27.1 k
13.2 k
6.3 k
2.9 k
100
20.4 k
10 k
4.8 k
2.2 k
C
INT
AD7710
V
BIAS
500
7.3 k
3.6 k
1.7 k
790
500
5.2 k
2.5 k
1.2 k
550
IMPEDANCE
>1G
HIGH
1000
4.1 k
2.0 k
970
440
1000
2.8 k
1.4 k
670
300
5000
1.1 k
560
270
120
5000
700
350
170
80
IN
–15–
The numbers in Tables IV and V assume a full-scale change on
the analog input. In any case, an error introduced due to longer
charging times is a gain error that can be removed using the
system calibration capabilities of the AD7710, provided that the
resultant span is within the span limits of the system calibration
techniques.
ANALOG INPUT FUNCTIONS
Analog Input Ranges
Both analog inputs are differential, programmable gain input
channels that can handle either unipolar or bipolar input signals.
The common-mode range of these inputs is from V
provided that the absolute value of the analog input voltage lies
between V
The dc input leakage current is 10 pA maximum at 25 C
( 1 nA over temperature). This results in a dc offset voltage
developed across the source impedance. However, this dc offset
effect can be compensated for by a combination of the differen-
tial input capability of the part and its system calibration mode.
Burnout Current
The AIN1(+) input of the AD7710 contains a 4.5 A current
source that can be turned on/off via the control register. This
current source can be used in checking that a transducer has not
burned out or gone open circuit before attempting to take mea-
surements on that channel. If the current is turned on and
allowed to flow into the transducer and a measurement of the
input voltage on the AIN1 input is taken, it can indicate that the
transducer has burned out or gone open circuit. For normal
operation, this burnout current is turned off by writing a 0 to
the BO bit in the control register.
Output Compensation Current
The AD7710 also contains a feature that allows the user to
implement cold junction compensation in thermocouple appli-
cations. This can be achieved using the output compensation
current from the I
can be turned on/off via the control register. Writing a 1 to the
IO bit of the control register enables this compensation current.
The compensation current provides a 20 A constant current
source that can be used in association with a thermistor or a
diode to provide cold junction compensation. A common
method of generating cold junction compensation is to use a
temperature dependent current flowing through a fixed resistor
to provide a voltage that is equal to the voltage developed across
the cold junction at any temperature in the expected ambient
range. In this case, the temperature coefficient of the compensa-
tion current is so low compared with the temperature coefficient
of the thermistor that it can be considered constant with tem-
perature. The temperature variation is then provided by the
variation of the thermistor’s resistance with temperature.
Normally, the cold junction compensation will be implemented
by applying the compensation voltage to the second input chan-
nel of the AD7710. Periodic conversion of this channel gives the
user a voltage that corresponds to the cold junction compensa-
tion voltage. This can be used to implement cold junction com-
pensation in software with the result from the thermocouple
input being adjusted according to the result in the compensation
channel. Alternatively, the voltage can be subtracted from the
input voltage in an analog fashion, thereby using only one chan-
nel of the AD7710.
SS
–30 mV and AV
OUT
pin of the device. Once again, this current
DD
+30 mV.
AD7710
SS
to AV
DD
,