2
AN1575.0
October 1, 2010
Amplifier Configuration (Figure 3)
The schematic of the op amp input stage with the
components supplied is shown in Figure 3, with a closed
loop gain of 10,000V/V. The circuit implements a Hi-Z
differential input with unbalanced common mode
impedance. The differential amplifier gain is expressed in
Equation 1:
For single-ended input with an inverting gain
G = -10,000V/V, the IN+ input is grounded and the
signal is supplied to the IN- input. VREF must be
connected to a reference voltage between the V+ and
V- supply rails. For non-inverting operation with
G = 10,001V/V, the IN- input is grounded and the
signal is supplied to the IN+ input. The non-inverting
gain is strongly dependent on any resistance from IN-
to GND. For good gain accuracy, a 0Ω resistor should
be installed on the empty R11 pad.
User-selectable Options
(Figures 3 and 4)
Component pads are included to enable a variety of
user-selectable circuits to be added to the amplifier
inputs, the VREF input, outputs and the amplifier
feedback loops.
A voltage divider can be added to establish a power
supply-tracking common mode reference using the VREF
input (see “ISL28433SOICEVAL1Z Schematic Diagram”
on page 4). The inverting and non-inverting inputs have
additional resistor and capacitor placements for adding
input attenuation or feedback capacitors (Figure 3).
The output (Figure 4) also has additional resistor and
capacitor placements for filtering and loading.
NOTE: Operational amplifiers are sensitive to output
capacitance and may oscillate. In the event of oscillation,
reduce output capacitance by using shorter cables, or
add a resistor in series with the output.
V
OUT
V
IN+
( V
IN-
) R
F
(• R
IN
)⁄– V
REF
+=
(EQ. 1)
R11
R6
R2
R5
R39R14
100
DNP
DNP
0
100
1M
OPEN
TO IN-A
TO IN+A
FROM OUT_A
FIGURE 3. INPUT STAGE
OPEN
C6
R20
DNP
C23
OPEN
C7
R15
0
DNP
R21
N+A
IN-A
OUT A
R51
J13
C15
R59
DNP
OPEN
0
FIGURE 4. OUTPUT STAGE
C14
OPEN
R55
DNP
R63
0
R67
DNP
OUT_A
TABLE 1. ISL28433TSSOPEVAL1Z and ISL28433MSOPEVAL1Z COMPONENTS PARTS LIST
DEVICE # DESCRIPTION COMMENTS
C1, C2 CAP, SMD, 1210, 4.7µF, 50V, 10%, X7R, ROHS Power Supply Decoupling
C3, C4 CAP, SMD, 0805, 0.1µF, 50V, 10%, X7R, ROHS Power Supply Decoupling
D1, D2 40V SCHOTTKY BARRIER DIODE Reverse Power Protection
R32, R33 RESISTOR, SMD, 0603, DNP, 1%, ROHS VREF Resistor Divider
C5 CAP, SMD, 1210, 4.7µF, 50V, 10%, X7R, ROHS VREF Supply Decoupling
R5, R7, R9, R14, R16,
R18, R35, R40
RESISTOR, SMD, 0603, 100Ω, 1%, 1/16W, ROHS Gain Setting Resistor
R39, R47, R49, R50 RESISTOR, SMD, 0603, 10MΩ, 1%, 1/16W, ROHS Gain Setting Feedback Resistor
R2-R4, R11-R13,
R20-R23, R25,R26,R34,
R38, R42, R43, R55-R58,
R67-70, R24, R27-R31,
R33, R45, R46, R59-R62
RESISTOR, SMD, 0603, DNP-PLACE HOLDER, ROHS User selectable resistors - not populated
U1 (ISL28433) ISL28433FBZ (SOIC), ISL28433FVZ (TSSOP),
IC-RAIL-TO-RAIL OP AMP, ROHS
Application Note 1575
