EVAL-AD7795 Datasheet, PDF (3/16 Pages) Analog Devices – Evaluation Board for the AD7795 16-Bit, Low Power Sigma-Delta ADC (6 Channels)

EVAL-AD7795
EVALUATION BOARD HARDWARE
POWER SUPPLIES
The AD7795 evaluation board is powered via the 5 V supply
from the USB connector, J1. This 5 V supply can be used to
power the AD7795 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 AD7795 can
be powered using an external 3 V or 5 V power supply via J3.
LINKS
There are eight 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.
SETUP CONDITIONS
Care should be taken before applying power and signals to the
evaluation board to ensure that all link positions are set per the
required operating mode. Table 2 shows the position in which
all the links are initially set.
SOCKETS
There are five sockets relevant to the operation of the AD7795
on this evaluation board. The functions of these sockets are
outlined in Table 3.
Table 1. Evaluation Board Link Settings
Link
LK1
LK2, LK3 LK4,
LK5, LK6
LK7
LK8
Default
Position
In
Out
Out
B
Description
This link is used to externally short AIN1(+) to AIN1(−). If VBIAS is enabled and directed to AIN1(−), a noise
analysis in this configuration can be performed. With this link removed, an external voltage can be applied to
AIN1(+)/AIN(−) using the SMB connectors.
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.
With the on-board temperature demonstration circuit selected in the software, LK6, when inserted, allows
current from the on-chip current source of the AD7795 to flow through the temperature demonstration
circuit. LK4 and LK5, when inserted, connect the 1 kΩ thermistor to AIN4(+)/AIN4(−), and with LK2 and LK3
inserted, the 5 kΩ precision resistor is used to generate the reference for the AD7795 so that a ratiometric
configuration of the temperature demonstration circuit is achieved.
LK7 is used to test the on-chip low-side power switch. If LK7 is in place, enabling the low-side power switch
via the PWR SW drop-down box in the Registers window (see Figure 4) turns on the LED, D2. Clearing this bit turns
off the LED.
LK8 is used to select the power source for AVDD on the AD7795. LK8 in Position A selects an external power
supply, supplied via J3. LK8 in Position B selects the 3.3 V regulated output from the on-board ADP3303
voltage regulator. LK8 in Position C selects the 5 V supply from the USB connector, J1.
Table 2. Initial Link and Switch Positions
Link No.
Position Description
LK1
In
AIN1(+) and AIN1(−) are shorted.
LK2, LK3
Out
Internal reference is used.
LK4, LK5
Out
AIN4(+) and AIN4(−) are not connected to the temperature demonstration circuit.
LK6
Out
IOUT2 is not connected to the temperature demonstration circuit.
LK7
Out
LED D1 is not connected to the low-side power switch of the AD7795.
LK8
B
The 3.3 V supply is used as AVDD for the AD7795.
Table 3. Socket Functions
Socket
AIN1+
AIN1−
REFIN1+
REFIN1−
J2
Description
Subminiature BNC (SMB) connector. The analog input signal for the AIN1(+) input of the AD7795 is applied to this socket.
Subminiature BNC (SMB) connector. The analog input signal for the AIN1(−) input of the AD7795 is applied to this socket.
Subminiature BNC (SMB) connector. This socket is used in conjunction with REFIN1− to apply an external reference to the
AD7795. The voltage for the REFIN1(+) input of the AD7795 is applied to this socket.
Subminiature BNC (SMB) connector. This socket is used in conjunction with REFIN1− to apply an external reference to the
AD7795.The voltage for the REFIN(−) input of the AD7795 is applied to this socket.
30-pin (2 × 15) straight header. This socket is used in conjunction with the prototype area to interface any signal to the AD7795.
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