EVAL-AD7799EBZ Analog Devices Inc, EVAL-AD7799EBZ Datasheet - Page 26

• Manufacturer Part Number: EVAL-AD7799EBZ
• Description: BOARD EVALUATION FOR AD7799
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD7799EBZ

• Number Of Adc's: 1
• Number Of Bits: 24
• Sampling Rate (per Second): 470
• Data Interface: Serial
• Inputs Per Adc: 3 Differential
• Input Range: ±VREF/gain
• Power (typ) @ Conditions: 2.5mW @ 470SPS
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 105°C
• Utilized Ic / Part: AD7799
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7798/AD7799
APPLICATIONS INFORMATION
The AD7798/AD7799 provide a low cost, high resolution
analog-to-digital function. Because the analog-to-digital
function is provided by a ∑-Δ architecture, the parts are more
immune to noisy environments, making them ideal for use in
sensor measurement and industrial and process-control
applications.
WEIGH SCALES
Figure 19 shows the AD7798/AD7799 being used in a weigh
scale application. The load cell is arranged in a bridge network
and gives a differential output voltage between its OUT+ and
OUT– terminals. Assuming a 5 V excitation voltage, the full-
scale output range from the transducer is 10 mV when the
sensitivity is 2 mV/V. The excitation voltage for the bridge can
be used to directly provide the reference for the ADC because
the reference input range includes the supply voltage.
A second advantage of using the AD7798/AD7799 in transducer-
based applications is that the low-side power switch can be fully
utilized in low power applications. The low-side power switch is
connected in series with the cold side of the bridge. In normal
OUT–
IN+
IN–
AV
DD
OUT+
REFIN(+)
AIN1(+)
AIN1(–)
AIN2(+)
AIN2(–)
REFIN(–)
PSW
Figure 19. Weigh Scales Using the AD7798/AD7799
GND
MUX
AV
DD
AV
GND
Rev. A | Page 26 of 28
AD7798/AD7799
DD
IN-AMP
INTERNAL
CLOCK
operation, the switch is closed and measurements can be taken.
In applications where power is of concern, the AD7798/AD7799
can be placed in standby mode, thus significantly reducing the
power consumed in the application. In addition, the low-side
power switch can be opened while in standby mode, thus
avoiding unnecessary power consumption by the front-end
transducer. When the part is taken out of standby mode and the
low-side power switch is closed, the user should ensure that the
front end circuitry is fully settled before attempting a read from
the AD7798/AD7799.
In Figure 19, temperature compensation is performed using a
thermistor. In addition, the reference voltage for the temperature
measurement is derived from a precision resistor in series with
the thermistor. This allows a ratiometric measurement—that is,
the ratio of the precision reference resistance to the thermistor
resistance is measured; therefore, variations of the reference
voltage do not affect the measurement.
ADC
Σ-Δ
REFERENCE
INTERFACE
DETECT
CONTROL
SERIAL
LOGIC
AND
DOUT/RDY
DIN
SCLK
CS
DV
DD