AD7785BRUZ Analog Devices Inc, AD7785BRUZ Datasheet - Page 30

• Manufacturer Part Number: AD7785BRUZ
• Description: IC ADC 20BIT SIGMA-DELTA 16TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD7785BRUZ

• Data Interface: MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Bits: 20
• Sampling Rate (per Second): 470
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP (0.173", 4.40mm Width)
• Resolution (bits): 20bit
• Input Channel Type: Differential
• Supply Voltage Range - Analogue: 2.7V To 5.25V
• Supply Voltage Range - Digital: 2.7V To 5.25V
• Supply: RoHS Compliant
• Sampling Rate: 470Hz
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7785EBZ - BOARD EVALUATION FOR AD7785
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7785
TEMPERATURE MEASUREMENT USING AN RTD
To optimize a 3-wire RTD configuration, two identically
matched current sources are required. The AD7785, which
contains two well-matched current sources, is ideally suited to
these applications. One possible 3-wire configuration is shown
in Figure 21. In this 3-wire configuration, the lead resistances
result in errors if only one current is used, as the excitation
current flows through RL1, developing a voltage error between
AIN1(+) and AIN1(–). In the scheme outlined, the second RTD
current source is used to compensate for the error introduced
by the excitation current flowing through RL1. The second RTD
current flows through RL2. Assuming RL1 and RL2 are equal
(the leads would normally be of the same material and of equal
RTD
R
RL1
RL2
RL3
REF
IOUT1
AIN1(+)
AIN1(–)
IOUT2
REFIN(+)
REFIN(–)
GND
Figure 21. RTD Application Using the AD7785
AV
AV
GND
DD
DD
BUF
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REFERENCE
BAND GAP
IN-AMP
INTERNAL
length), and IOUT1 and IOUT2 match, the error voltage across
RL2 equals the error voltage across RL1, and no error voltage
is developed between AIN1(+) and AIN1(–). The voltage is
developed twice across RL3. However, because this is a
common- mode voltage, it does not introduce errors. The
reference voltage for the AD7785 is also generated using one of
these matched current sources. It is developed using a precision
resistor and applied to the differential reference pins of the
ADC. This scheme ensures that the analog input voltage span
remains ratiometric to the reference voltage. Any errors in the
analog input voltage due to the temperature drift of the excita-
tion current are compensated by the variation of the reference
voltage.
CLOCK
CLK
REFIN(+) REFIN(–)
ADC
Σ-Δ
GND
AD7785
INTERFACE
CONTROL
SERIAL
LOGIC
AND
DOUT/RDY
DIN
SCLK
CS
DV
DD