EVAL-AD7798EB Datasheet, PDF (2/7 Pages) Analog Devices – 16-Bit Low Power Σ-Δ ADC (3 Channels)

EVAL-AD7798EB
Preliminary Technical Data
There are ten link options which must be set for the required operating setup before using the evaluation board. The functions of these
link options are outlined below.
Table 1.Evaluation Board Link Settings
Link
LK1, LK2
Default
In
Description
These links are used to connect the AIN1(+) and AIN1(-) inputs to a reference voltage which
equals AVDD /2. With this configuration, a noise analysis can be performed. With these links
removed, an external voltage may be applied to AIN1 using the SMB connectors.
LK3, LK4, LK5, LK6 Out
These links are used to connect the on board temperature demonstration circuit to the ADC,
and must all be in place when attempting to measure ambient temperature.
LK7, LK8
LK9
LK10
When LK3 and LK4 are inserted, the 1KΩ thermistor is connected to AIN2. With LK5 and
LK6 in place, a 5KΩ precision resistor is used to generate the reference. This results in a
ratiometric configuration.
In
A resistor divider network generates a voltage equal to AVDD /2 which can be used as the
reference for the AD77998 With LK7 and LK8 in place, AVDD /2 is connected to REFIN(+)
and REFIN(-) is connected to GND. To use another reference source, remove LK7 and LK8.
B
LK9 is used to select the power source for AVDD on the AD7798. LK9 in position A selects an
external power supply, supplied via J3. LK9 in position B selects the 3.3V regulated output from
the onboard ADP3303 voltage regulator. LK9 in position C selects the 5V supply from the USB
connector, J1.
In
LK10 is used to test the on chip low side power switch. With LK10 in place, enabling the low-
side power switch in software by setting a bit in the configuration register turns on the LED, D2
Clearing this bit turns off the LED.
SET-UP CONDITIONS
Care should be taken before applying power and signals to the evaluation board to ensure that all link positions are as per the required
operating mode. Table 1 shows the position in which all the links are set when the evaluation board is sent out.
Table 2: Initial Link and Switch Positions
Link No.
LK1 - LK2
LK3 – LK6
LK7 – LK8
LK9
LK10
Position
In
Out
In
B
In
Function
AIN1(+) and AIN1(-) are shorted to the reference voltage
The demonstration circuit is disconnected from the AD7798
The reference voltage is set to 1.65V (3.3V/2)
The 3.3V supply is used as AVDD for the AD7798.
LED D2 is connected to the Low Side Power Switch of the
AD7798
EVALUATION BOARD INTERFACING
Interfacing to the evaluation board is via a standard USB Connector, J1. J1 is used to connect the evaluation board to the USB port of a
PC. A standard USB connector cable is included with the AD7798 evaluation board to allow the evaluation board to interface with the
PC's USB port. As the board is powered via the USB connector, there is no need for an external power supply, although one may be
connected if preferred via J3.
Communication between the AD7798 and the PC is over the USB/SPI interface. The onboard USB controller (U2) controls this
communication. Remember, the AD7798 Evaluation Board Software should be installed (using the supplied AD7798 Evaluation Board
CD ROM) BEFORE connecting the board to the PC.
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