AD623-EVAL Analog Devices Inc, AD623-EVAL Datasheet - Page 2

• Manufacturer Part Number: AD623-EVAL
• Description: BOARD EVAL/DEMO R-R AMP AD623
• Manufacturer: Analog Devices Inc
• Type: Amplifiers: OP Ampsr

Specifications of AD623-EVAL

• Rohs Status: RoHS non-compliant
• Contents: Evaluation Board
• For Use With/related Products: AD623
• Lead Free Status / Rohs Status: Not Compliant

EVAL-AD623EB
CIRCUIT OPTIONS
Single-Supply Operation
A jumper is provided to select between single or dual power
supplies. The board is shipped with W14 in the dual-supply
position. To convert to single supply, place W14 in the position
marked with a ground symbol.
Gain Adjustment
The default gain of the AD623 is unity; installing a resistor at R
enables its adjustment. R
following equation, or selected from Table 1:
Table 1. AD623 Standard Value Gain Resistors
Desired
Gain
2
5
10
20
33
40
50
65
100
200
500
1000
External Reference or Offset Adjustment
When shipped, the reference of the EVAL-AD623EB is
connected to ground. Certain single-supply applications (for
example, an A/D converter connected to the AD623’s output)
require a symmetrical output voltage centered on a nonzero
value. The reference may be equal to half the supply, or an
application-specific voltage provided by an A/D converter. The
user may install a jumper at W13 and connect an external
reference to the EXT_REF pin. To maintain proper operation of
the in-amp, the reference should be provided by a voltage
source.
Similarly, provision is made for an offset adjustment of ±1.12 V
by installing the parts listed in Table 4. Although it may be used
with single or dual power supply connection, A1 requires a dual
supply. To enable the offset feature, install a shunt in position
W11. To adjust the offset of the AD623, ground both inputs and
measure the output voltage. Adjust potentiometer R1 for 0 V.
LOAD RESISTOR
Though a load resistor is not required for normal operation, one
may be inserted at position R8.
11 k
5.23 k
3.09 k
2.55 k
2.05 k
1.58 k
1.02 k
1% Standard
Value of R
100 k
24.9 k
499
200
100
R
G
G
G
(Ω)
= 100 kΩ/(G – 1)
may be calculated according to the
Calculated Gain Using
Standard 1% Resistors
2
5.02
10.09
20.12
33.36
40.21
49.78
64.29
99.04
201.4
501
1001
Rev. 0 | Page 2 of 4
G
GUARD DRIVERS
When interference from sources such as power lines must be
reduced to levels below those provided by standard shielded
cable, guard drivers can be effective. A guard equalizes the ac
potential between the in-amp input and the cable shield of the
line, effectively reducing the low frequency interference voltage.
A1 in Figure 2 is a dual op amp AD708H driving the shield(s) of
the input cable(s) from the AD623’s gain resistor pins. The
voltages at these pins are equal to the input voltages plus 0.6 V
(refer to Figure 40 in the AD623 data sheet.)
The EVAL-AD623EB provides single and differential guards.
Differential guards drive the shields with essentially the same
signals as the inputs, while the single guard may be used for
dual conductor cables. In this mode, the +GUARD will drive the
shield at ½(VIN DIFF) + 0.6 V.
To activate the guard drivers, +V
connected. For shielded cables at both inputs, install jumpers
W1, W2, W8, and W5.
Using a Single Guard
For gains greater than 1, resistors R6 and R11 (which are each
half the calculated resistance of R
installed. For a gain of 1, either position R6 or R11 may be
shorted to enable the guard driver input. Connect the shield to
the +GUARD. On the header pins that do not bear the ground
symbol, insert a shunt across position W1.
The guard drivers may be assembled using the components
listed in Table 4.
POWER
INPUT
Figure 2. Component Location of In-Amp Evaluation Board
AUX
G
), and W1, W2, and W10 are
and –V
AUX
must be
OUTPUT
04223-0-002