Evaluation Board User Guide UG-078
Rev. 0 | Page 3 of 16
EVALUATION BOARD HARDWARE
POWER SUPPLIES
The AD7780 evaluation board is powered via the 5 V supply
from the USB connector, J1. This 5 V supply can be used to
power the AD7780 directly. A 3.3 V regulated voltage from the
on-board ADP3303 (a high precision, low power, 3.3 V output
voltage regulator) can also be used. Alternatively, the AD7780 can
be powered using an external 3 V or 5 V power supply via J2.
LINKS
There are sixteen groups of link options that must be set for the
required operating setup before using the evaluation board. The
functions of these link options are outlined in Table 1 .
Table 1. Evaluation Board Link Settings
Link Default Description
LK1, LK2 In These links are used to connect the AIN(+) and AIN(−) inputs to AVDD/2. With this configuration, a noise
analysis can be performed. With these links removed, an external voltage may be applied to AIN using the
SMB connectors.
LK3, LK4 In With LK3 and LK4 in place, AVDD is used as the reference to the AD7780. REFIN(+) is connected to AVDD and
REFIN(−) is connected to GND. To use another reference source, remove LK3 and LK4.
LK5 3.3 V LK5 is used to select the power source for AVDD on the AD7780.
In Position A, LK5 selects an external power supply, supplied via J2.
In Position B, LK5 selects the 3.3 V regulated output from the on-board ADP3303 voltage regulator.
In Position C, LK5 selects the 5 V supply from the USB connector, J1.
LK6 to LK11 In These links connect the serial interface pins of the AD7780 to the SPI interface of the microcontroller. The
links should be in place to use the AD7780 evaluation board software. With these links removed, the AD7780
can be interfaced to an external microcontroller.
LK12, LK13, LK14 In These links are used for the bridge power-down switch. With LK12 inserted, the bridge power-down switch is
connected to AVDD through an LED. When the bridge power-down switch is closed, the LED turns on. LK13
should be open when LK12 is inserted.
LK13 and LK14 are used when a load cell is connected to Header J4. LK12 should be left open. With LK13
inserted, the bridge power-down switch is connected to Header J4. The low side of the load cell can be
connected to GND through the bridge power-down switch. With LK14 inserted, the low side of the load cell is
connected directly to GND. The REFIN(−) terminal should be shorted to the GND/PSW terminal on Header J4
to enable the previous functions.
LK15 10 Hz
LK15 is used to select the output data rate for the AD7780. With LK15 in Position 10 Hz, the output data rate is
set to 10 Hz. When LK15 is in Position 16.7 Hz, the output data rate is set to 16.7 Hz.
LK16 128
LK16 is used to select the gain of the AD7780. With LK16 in Position 1, the gain is set to 1. With LK16 in
Position 128, the gain of the AD7780 is set to 128.
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