an1499

Application Note 1499
ISL28133EVAL1Z High-Gain Evaluation Board
User’s Guide
Introduction
Reference Documents
The maximum useful signal range of a high gain DC
amplifier is limited by the amplifiers own DC offset and
low frequency noise. For battery powered amplifiers the
problem is further compounded due to limits of low
battery voltage. For example, the useful input voltage
range of an ideal amplifier with 10kV/V gain operating
from a 3V Lithium cell would be 300µV, which would
drive the to the maximum possible +3V output. A
standard low offset amplifier with 100µV VOS would
reduce the maximum useful input voltage range from
300µV to 200µV, since the input offset voltage alone
would drive the amplifier output to 10k times that, taking
up 1V of the 3V total available voltage range. Further
reductions due to offset voltage drift, low frequency 1/f
noise, and the inability to swing the output close to the
power supply rails can limit the best amplifiers to DC
gains no higher than several hundred V/V.
• ISL28133 Data Sheet, FN6560
Evaluation Board Key Features
The ISL28133EVAL1Z is designed to enable the IC to
operate from a single supply, +2.4VDC to +5.5VDC or
from split supplies, ±1.2VDC to ±2.75V. The board is
configured for a single op amp connected for
single-ended or differential input with a closed loop gain
of 10,000. A single external reference voltage (VREF) pin
and provisions for a user-selectable voltage divider-filter
are included.
Power Supplies (Figure 2)
External power connections are made through the V+,
V-, VREF, and Ground connections on the evaluation
board. For single supply operation, the -V and Ground
pins are tied together to the power supply negative
terminal. For split supplies, +V and -V terminals connect
to their respective supply terminals. De-coupling
capacitors C2 and C4 provide low-frequency
power-supply filtering, while four additional capacitors,
C1, C5, C7 and C8, which are connected close to the
part, filter out high frequency noise. Anti-reverse diodes
D1 and D2 (optional) protect the circuit in the case of
accidental polarity reversal.
The ISL28133 chopper stabilized rail-to-rail op amp
features a low 8µV maximum VOS over-temperature and
a 0.1Hz 1/f noise corner frequency enabling very high
gain single-stage DC amplifiers that can operate from
single cell batteries while consuming only 20µA of
current. The ISL28133EVAL1Z evaluation board is
configured as a precision high-gain (G = 10,000)
differential amplifier and demonstrates the level of
performance possible with this type of amplifier while
operating from battery voltages as low as 2.4V.
The circuit can operate from a single supply or from dual
supplies. The VREF pin can be connected to ground to
establish a ground referenced input for split supply
operation, or can be externally set to any reference level
for single supply operation.
RF
1MΩ
IN RININ-
IN-
IN+
V+
VCM
VREF
VREF
GND
IN+
0Ω
0Ω
VOUT
V+
VM
100Ω
IN +
VP
-
100Ω
RIN+
ISL28133
RG
RL
1MΩ
OPEN
OPEN
FIGURE 1. BASIC AMPLIFIER CONFIGURATION
October 2, 2009
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Application Note 1499
J11
C5
DNP
R16
C8
D2 S1AB
A voltage divider and filter option (Figure 3) can be
added to establish a power supply-tracking common
mode reference at the VREF input. The inverting and
non-inverting inputs have additional resistor placements
for adding input attenuation, or to establish input DC
offsets through the VREF pin.
FIGURE 2. POWER SUPPLY CIRCUIT
Amplifier Configuration
(Figure 2)
The output (Figure 4) also has additional resistor and
capacitor placements for filtering and loading.
The schematic of the op amp with the components
supplied is shown in Figure 2, with a closed loop gain of
10,000. The circuit implements a Hi-Z differential input
with unbalanced common mode impedance. The
differential amplifier gain is expressed in Equation 1:
V OUT = ( V IN+ – V IN- ) • ( R F ⁄ R IN ) + V REF
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.
0.1µF
D1 S1AB
C7
C4 1µF
0.1µF
C1
VREF
J9
C2 1µF
0.01µF
R4
DNP
J13
J10
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.
(EQ. 1)
IN
where: RF = RG and RIN+ = RIN- and the differential
input impedance is ~1M with VREF at GND. The IN- input
connects to the amplifier summing junction and it’s
impedance to ground is a low 100Ω. The impedance of the
IN+ input to ground is much higher at 1.001MΩ. to VREF.
-
J1
R1
R5
R9
OPEN
R11
0
10k
100k
DNP
DNP
V+
R7
J8
0.01µF
V-
J7
FROM OUT
TO IN IN
+
R12
J2
R2
TO IN +
10k
DNP
R13
R15
DNP
100k
VREF
FIGURE 3. INPUT STAGE
R18
OUTPUT
DNP
OPEN
R17
J12
0
C6
For single-ended input inverting operation (G = -10001),
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 (G = 10,000), 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 R7 pads.
FIGURE 4. OUTPUT STAGE
TABLE 1. ISL28133EVAL1Z COMPONENTS PARTS LIST
DEVICE #
DESCRIPTION
COMMENTS
C2, C4
CAP, SMD, 0603, 1µF, 25V, 10%, X7R, ROHS
Power Supply Decoupling
C1, C5
CAP, SMD, 0603, 0.1µF, 25V, 10%, X7R, ROHS
Power Supply Decoupling
C7, C8
CAP, SMD, 0603, 0.01µF, 25V, 10%, X7R , ROHS
Power Supply Decoupling
C3, C6
CAP, SMD, 0603, DNP-PLACE HOLDER, ROHS
User selectable capacitors - not populated
D1, D2
DIODE-RECTIFIER, SMD, SOD-123, 2P, 40V, 0.5A, ROHS Reverse Power Protection
U1 (ISL28133EVAL1Z)
ISL28133FHZ-T7, IC-RAIL-TO-RAIL OP AMP, SOT-23, ROHS
R1-R4, R6-R8, R10, R13, RESISTOR, SMD, 0603, 0.1%, MF, DNP-PLACE HOLDER
R14, R16, R17, R19, R21
User selectable resistors - not populated
R5, R18
RES, SMD, 0603, 0Ω, 1/10W, TF, ROHS
0Ω user selectable resistors
R9, R12
RES, SMD, 0603, 100, 1/10W, 1%, TF, ROHS
Gain resistors
R11, R15
RES, SMD, 0603, 1M, 1/10W, 1%, TF, ROHS
Gain resistors
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Application Note 1499
ISL28133EVAL1Z Top View
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the
reader is cautioned to verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
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ISL28133EVAL1Z Schematic Diagram
J8
S1AB
R16
DNP
R4
S1AB
VREF
J11
C4
1µF
D2
J10
C2
1µF
D1
J9
J13
V+
DNP
J7
V-
4
J6
1M
0
DNP
R18
100
C7
0.1µF
C1
ENABLE
SOT23_6
J14
R19
DNP
S1
2
3
1
R20
DNP
R21
DNP
R13
R15
DNP
1M
VREF
0.1µF
100
C8
R2
DNP
0.01µF
J2
6
2 GENERIC 5
PACK.
3
4
0.01µF
R12
C5
IN +
DNP
OPEN
R17
U1
1
J12
C6
C3
R14
R9
0
DNP
R3
DNP
J5
R5
OPEN
R11
DNP
R10
DNP
R6
R8
DNP
R7
R1
DNP
J1
OUT
OUTPUT
Application Note 1499
IN -
NODE
J4
IN+
J3
IN-
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