AD7785BRUZ Analog Devices Inc, AD7785BRUZ Datasheet - Page 20

• 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
ADC CIRCUIT INFORMATION
OVERVIEW
The AD7785 is a low power ADC that incorporates a ∑-Δ
modulator, a buffer, reference, in-amp, and an on-chip digital
filter intended for the measurement of wide dynamic range, low
frequency signals such as those in pressure transducers, weigh
scales, and temperature measurement applications.
The part has three differential inputs that can be buffered or
unbuffered. The device can be operated with the internal 1.17 V
reference, or an external reference can be used. Figure 12 shows
the basic connections required to operate the part.
The output rate of the AD7785 (f
allowable update rates, along with their corresponding settling
times, are listed in Table 14. Normal mode rejection is the major
function of the digital filter. Simultaneous 50 Hz and 60 Hz
rejection is optimized when the update rate equals 16.7 Hz or
less as notches are placed at both 50 Hz and 60 Hz with these
update rates (see Figure 14.)
THERMOCOUPLE
JUNCTION
R
R
C
ADC
) is user-programmable. The
AIN1(+)
AIN1(–)
R
REF
–100
–20
–40
–60
–80
0
AIN2(+)
AIN2(–)
REFIN(+)
REFIN(–)
IOUT2
V
0
BIAS
Figure 13. Filter Profile with Update Rate = 4.17 Hz
GND
Figure 12. Basic Connection Diagram
20
MUX
AV
AV
GND
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DD
DD
40
AV
FREQUENCY (Hz)
DD
BUF
60
REFERENCE
BAND GAP
The AD7785 uses slightly different filter types, depending on
the output update rate so that the rejection of quantization
noise and device noise is optimized. When the update rate is
from 4.17 Hz to 12.5 Hz, a Sinc3 filter, along with an averaging
filter, is used. When the update rate is from 16.7 Hz to 39 Hz, a
modified Sinc3 filter is used. This filter provides simultaneous
50 Hz/60 Hz rejection when the update rate equals 16.7 Hz. A
Sinc4 filter is used when the update rate is from 50 Hz to
242 Hz. Finally, an integrate-only filter is used when the update
rate equals 470 Hz.
Figure 13 to Figure 16 show the frequency response of the
different filter types for several update rates.
IN-AMP
80
INTERNAL
CLOCK
CLK
100
REFIN(+) REFIN(–)
ADC
Σ-Δ
GND
120
AD7785
INTERFACE
CONTROL
SERIAL
LOGIC
AND
DOUT/RDY
DIN
SCLK
CS
DV
DD