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Application Note 1669
ISL70227SRH Evaluation Board User’s Guide
Introduction
The ISL70227MHEVAL1Z evaluation board is designed to
evaluate the performance of the rad hard ISL70227SRH 36V
Precision Low Power Operational Amplifier. The ISL70227SRH
can operate from a dual supply with a 4.5V to 36V supply
range. The ISL70227SRH features very low power, low offset
voltage and low temperature drift, making it ideal for
applications for precision instrumentation, current sensing and
power supply, and industrial process controls.
Reference Documents
• ISL70227SRH Data Sheet, FN7925
Evaluation Board Key Features
• Wide Supply Operation: 4.5V to 36V
• Single-Ended or Differential Input Operation
•External VREF Input
• Banana Jack Connectors for Power Supply and VREF Inputs
• BNC Connectors for Op Amp Input and Output Terminals
• Convenient PCB Pads for Op Amp Input/Output Impedance
Loading
Power Supplies
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 power supply
terminals. De-coupling capacitors C2, C3, C4 and C6 connect
to their respective supplies through R11 and R15 resistors.
These resistors are 100Ω but can be changed by the user to
provide additional power supply filtering, or to reduce the
voltage rate-of-rise to less than ±1V/µs. Two additional
capacitors, C5 and C7, are connected close to the part to filter
out high frequency noise. Anti-reverse diode D1 protects the
circuit in the momentary case of accidentally reversing the
power supplies to the evaluation board. 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.
Amplifier Configuration
A simplified schematic of the evaluation board is shown in
Figure 2. The input stage with the components supplied is
shown in Figure 3, with a closed loop gain of 10V/V. The
differential amplifier gain is expressed in Equation 1:
For single-ended input with an inverting gain G = -10V/V, the
IN+ input is grounded and the signal is supplied to the IN-
input. VREF can be connected to a reference voltage between
the V+ and V- supply rails. For non-inverting operation with
G = 11V/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 R5 pad. The VREF
pin must be connected to ground to establish a ground
referenced input for dual supply operation, or can be externally
set to any reference level for single supply operation. VREF
should not be left floating.
0.01µF0.01µF
R15
R11
D1
C2 C4
C5 C7
J7
J10
J8 J9
J5
J6
100
100
1µF 1µF
VREF
V+V-
FIGURE 1. POWER SUPPLY CIRCUIT
0.1µF0.1µF
C3 C6
VOUT VIN+
(VIN-)RF
(• RIN)⁄–VREF
+= (EQ. 1)
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 |Copyright Intersil Americas Inc. 2011. All Rights Reserved
Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.
All other trademarks mentioned are the property of their respective owners.
September 23, 2011
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Application Note 1669
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User-selectable Options
Component pads are included to enable a variety of
user-selectable circuits to be added to the amplifier VREF,
inputs, outputs, and the amplifier feedback loops.
A voltage divider (Figure 3, R6 and R12) can be added to
establish a power supply-tracking common mode reference
using the VREF input. The input stages (see Figure 3) have
additional resistor and/or capacitor pads that may be used to
add voltage divider networks or feedback networks for adding
input attenuation, or to establish input DC offsets through the
VREF pin. The output stages (see Figure 4) have additional
resistor and capacitor placements for 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.
FIGURE 2. BASIC AMPLIFIER CONFIGURATION
FIGURE 3. INPUT STAGE (1/2) FIGURE 4. OUTPUT STAGE (1/2)
IN-
IN+
RF
VREF
IN -
IN +
GND
100kΩ
RREF+
VOUT
ISL70227(1/2)
VP
V-
0Ω
VN
VCM
IN-
IN+
VREF
V+
RIN-
10kΩ
RIN+
10kΩ
-
+
100kΩ
RL
DNP
C1
R5
R3
J2
J1
R1
R2
R10
R12R6
R9R4
DNP
DNP
DNP
OPEN
DNP
10k 100k
100k
10k
0
VREF IN+
IN-
OUTPUT
R26
C6
C8
R28
DNP
OPEN
OPEN
0
FROM OUTPUT
Application Note 1669
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TABLE 1. ISL70227MHEVAL1Z COMPONENTS PARTS LIST
DEVICE # DESCRIPTION COMMENTS
C2, C4 CAP, SMD, 1210, 1µF, 50V, 10%, X7R, ROHS Power Supply Decoupling
C3, C6 CAP, SMD, 0805, 0.1µF, 50V, 10%, X7R, ROHS Power Supply Decoupling
C5, C7 CAP, SMD, 0603, 0.01µF, 50V, 10%, X7R, ROHS Power Supply Decoupling
C1, C8-C12 CAP, SMD, 0603, DNP-PLACE HOLDER, ROHS User selectable capacitors - not populated
D1 DIODE-RECTIFIER, SMD, SOD-123, 2P, 40V, 0.5A, ROHS Reverse Power Protection
U1 ISL70227SRHM, DUAL OP-AMP, 10 Ld. FLATPAK
R1, R2, R5-R8, R14, R20, R23, R24, RESISTOR, SMD, 0603, 0.1%, MF, DNP-PLACE HOLDER User selectable resistors - not populated
R3, R20-R22 RES, SMD, 0603, 0Ω, 1/10W, TF, ROHS Zero ohm resistors
R4, R10, R17, R18 RES, SMD, 0603, 10k, 1/10W, 1%, TF, ROHS Gain resistors
R10, R12, R13, R16 RES, SMD, 0603, 100k, 1/10W, 1%, TF, ROHS Gain resistors
Application Note 1669
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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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FIGURE 5. ISL70227MHEVAL1Z TOP VIEW
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FIGURE 6. ISL70227MHEVAL1Z SCHEMATIC DIAGRAM
