AD7745ARUZ-REEL Analog Devices Inc, AD7745ARUZ-REEL Datasheet - Page 20

• Manufacturer Part Number: AD7745ARUZ-REEL
• Description: IC,Converter, Other/Special/Miscellaneous,TSSOP,16PIN
• Manufacturer: Analog Devices Inc
• Type: Capacitance-to-Digital Converterr

Specifications of AD7745ARUZ-REEL

• Design Resources: Extending the Capacitive Input Range of AD7745/AD7746 (CN0129)
• Resolution (bits): 24 b
• Data Interface: Serial
• Voltage Supply Source: Single Supply
• Voltage - Supply: 2.7 V ~ 5.25 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sampling Rate (per Second): -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7745/AD7746
CIRCUIT DESCRIPTION
CIN1(+)
CIN1(–)
OVERVIEW
The AD7745/AD7746 core is a high precision converter con-
sisting of a second order (Σ-Δ or charge balancing) modulator
and a third order digital filter. It works as a CDC for the capa-
citive inputs and as a classic ADC for the voltage input or for
the voltage from a temperature sensor.
In addition to the converter, the AD7745/AD7746 integrates a
multiplexer, an excitation source and CAPDACs for the capa-
citive inputs, a temperature sensor, a voltage reference for the
voltage and temperature inputs, a complete clock generator, a
control and calibration logic, and an I
interface.
The AD7745 has one capacitive input, while the AD7746 has
two capacitive inputs. All other features and specifications are
identical for both parts.
CAPACITANCE-TO-DIGITAL CONVERTER
Figure 28 shows the CDC simplified functional diagram. The
measured capacitance C
source and the Σ-Δ modulator input. A square-wave excitation
signal is applied on the C
modulator continuously samples the charge going through the
C
stream of 0s and 1s containing the information in 0 and 1
density. The data from the digital filter is scaled, applying the
calibration coefficients, and the final result can be read through
the serial interface.
The AD7745/AD7746 is designed for floating capacitive
sensors. Therefore, both C
ground.
VIN(+)
VIN(–)
EXCA
EXCB
X
. The digital filter processes the modulator output, which is a
SENSOR
TEMP
CAP DAC
EXCITATION
CAP DAC
Figure 26. AD7745 Block Diagram
MUX
REFIN(+) REFIN(–)
X
X
is connected between the excitation
X
MODULATOR
during the conversion and the
GENERATOR
24-BIT Σ-∆
plates have to be isolated from
CLOCK
2
C-compatible serial
REFERENCE
DIGITAL
FILTER
VOLTAGE
VDD
CONTROL LOGIC
CALIBRATION
GND
AD7745
INTERFACE
SERIAL
I
2
C
SDA
SCL
RDY
Rev. 0 | Page 20 of 28
CIN1(+)
CIN1(–)
CIN2(+)
CIN2(–)
EXCITATION SOURCE
The two excitation pins EXCA and EXCB are independently
programmable. They are identically functional and therefore
either of them can be used for the capacitive sensor excitation.
On the 2-channel AD7746 using a separate excitation pin for
each capacitive channel is recommended.
VIN(+)
VIN(–)
EXC1
EXC2
C
X
SENSOR
TEMP
EXCITATION
CAP DAC
CAP DAC
EXC
CIN
Figure 28. CDC Simplified Block Diagram
Figure 27. AD7746 Block Diagram
MUX
CAPACITANCE TO DIGITAL CONVERTER
MODULATOR
REFIN(+) REFIN(–)
GENERATOR
24-BIT Σ-∆
EXCITATION
CLOCK
MODULATOR
GENERATOR
24-BIT Σ-∆
CLOCK
(CDC)
DIGITAL
FILTER
REFERENCE
DIGITAL
FILTER
VOLTAGE
VDD
CONTROL LOGIC
GND
CALIBRATION
DATA
AD7746
INTERFACE
SERIAL
I
2
C
SDA
SCL
RDY