2
AN1289.0
February 12, 2007
Amplifier Configuration
(Figure 2)
The schematic of each of the 4 Op Amps with the
components supplied is shown in Figure 2. The circuit
implements a differential input instrumentation amp with a
closed loop gain of 101. The circuit can operate from a
single 2.4VDC to +5VDC supply, or from dual supplies from
±1.2VDC to ±2.5VDC.The output common mode reference
is applied to the VREF pin, and has a range from ground
(VM) to VP.
User-selectable Options
(Figure 3)
Component pads are included to enable a variety of user-
selectable circuits to be added to the amplifier differential
inputs, the VREF input, and the amplifier feedback loop. A
voltage divider and filter option can be added to establish a
power supply tracking common mode reference at the VREF
input, or a coaxial connection to the ISL28470 FB+ pin can
be made at the FB+ BNC connector. The differential inputs
have additional resistor placements for adding input
attenuation, or to establish input DC offsets through the
VREF pin.
FIGURE 3. COMPONENT-SELECTABLE OPTIONS
J
9
R
6
R
5
C
3
OPEN
DNP
DNP
VREFA
V+
V-
J
4
VREFA
1
R
13
R
15
R
17
R
18
R
21
R
22
R
23
R
20
R
19
R
16
R
14
J
8
J
10
FB+A
-INA
+INA
0
0
0
DNP
DNP
DNP
DNP
DNP
1k
100k
100k
VREFA
ISL28470EVAL1Z Components Parts List
DEVICE #
DESCRIPTION
COMMENTS
C
1
, C
2
CAP-TANTALUM, SMD, D,4.7µF, 50V, 10%, LOW ESR, ROHS Power Supply Decoupling
C
7
, C
8
CAP, SMD, 0603, 0.01µF, 25V, 10%, X7R, ROHS
Power Supply Decoupling
C
9
, C
10
CAP, SMD, 0805, 0.1µF, 25V,10%, X7R, ROHS
Power Supply Decoupling
C
3
-C
6
CAP, SMD, 0805, DNP-PLACE HOLDER, ROHS
Optional VREF Filter
Not Populated
C
11
-C
18
CAP, SMD, 0805, DNP-PLACE HOLDER, ROHS
Optional Amplifier Feedback Caps
Not Populated
D
1
, D
2
DIODE-RECTIFIER, SMD, MELF, 2 Ld, 50V, 1A, GPP, ROHS
Reverse Power Protection
U1
ISL28470FAZIC INSTRUMENTATION AMP, 28P, QSOP,
ROHS
R
13
, R
14
-R
16
, R
19
, R
22
, R
24
-R
27
, R
30
, R
33
,
R
35
-R
38
,R
41
, R
44
, R
46
-R
49
, R
52
, R
55
, R
69
,
R
71
, R
73
, R
75
RESISTOR, SMD, 0603, 0.1%, MF, DNP-PLACE HOLDER
User Selectable Resistors
Not Populated
R
18
, R
21
, R
29
, R
32
, R
40
, R
43
, R
51
, R
54
, R
58
,
R
60
, R
63
, R
66
RES, SMD, 0603, 0
Ω
, 1/16W, TF, ROHS
0
Ω
User Selectable Resistors
R
17
, R
28
, R
39
, R
50
RES, SMD, 0603, 1k, 1/10W, 1%, TF, ROHS
R
G
Gain Resistors
R
59
, R
61
, R
65
, R
67
, R
70
, R
72
, R
74
, R
76
RES, SMD, 0603, 10k, 1/10W, 1%, TF, ROHS
R
20
, R
23
, R
31
, R
34
, R
42
, R
45
, R
53
, R
56
, R
57
,
R
62
, R
64
, R
68
RES, SMD, 0603, 100k, 1/10W, 1%, TF, ROHS
R
F
Gain Resistors
R
1
-R
4
RES, SMD, 0805, 0
Ω
, 1/8W, TF, ROHS
0
Ω
User Selectable Resistors
R
5
-R
12
RES, SMD, 0805, DNP-PLACE HOLDER, ROHS
User Selectable Resistors
Not Populated
S
1
-S
4
SWITCH-SEALED MINI TOGGLE, TH, 3P, SP, ON/NONE/ON,
GOLD
Enable/Disable Select Switches
Application Note 1289
